It is essential to restrict the growth of microorganisms in raw fresh milk. This can be achieved by means of prompt cooling or chilling of milk to below 100C within 4 hours of milking and, holding it cold till processed or marketed. Chilling of milk is a surest means of controlling growth of pathogenic and non-pathogenic organisms but it does not render safe for human consumption until processed. Chilling can be done at the farm, collection centre, chilling centre or main dairy by several methods.However, long storage of chilled milk at low temperature (below 4°C) causes changes in microbial population and some physico-chemical properties affecting its keeping quality. Several containers of varying size, shape, type and capacity are used for chilling and storage of milk. The material and constructional design of equipment and utensils are most important for milk chilling and its storage.
Showing posts with label Milk Reception. Show all posts
Showing posts with label Milk Reception. Show all posts
Storage of Milk
i. Purpose
The purpose of storage of milk at different operational points is described below:
At Production/Collecting/ChillingCentre:
- For pooling and bulking from small producers until it is transported to chilling centres/processing plants.
- For chilling and holding at chilling centres until picked up by tankers.
- To handle milk from large producers.
At Processing Centre
- For storing raw milk as received from chilling centres till taken up for processing.
- For storing processed milk till taken up for packaging or bulk dispensing.
- For storing milk products in liquid state during manufacturing.
- Intermediate storage between processes.
For Transportation in bulk by road tankers
- For transportation of pre-cooled milk from collection and chilling centres located in rural areas of production to processing plants located in urban areas of high density consumption.
- For transportation in container service from process plant to bulk dispensing centres.
- For Transportation in bulk by rail tankers
- For transportation of pre-cooled milk comparatively large quantity of raw milk from chilling centers located close to rail tracks to processing plants.
- For transporting processed milk from area of high production to cities located at vast distances.
Modern dairy plants hold both raw and pasteurized milks. Normally the milk storage capacity is equal to one day’s intake. So, large milk tanks & silos are being installed at dairy plants with the following objectives:
- To maintain milk at a low temperature so as to prevent any deterioration in quality prior to processing /product manufacture.
- To facilitate bulking of raw milk supply to ensure uniform composition.
- To allow for uninterrupted operation during processing.
- To facilitate standardization of milk.
ii. Storage Equipment
Guidelines Deciding Suitability of Storage Facilities: The following guidelines are observed while deciding the suitability of storage facility for specific purposes:
Modern dairy operations necessitate storage facilities to allow continuous(uninterrupted) operation, for extended period of time, during processing. The type of storage facility to be provided depends on various factors. When large volume of milk is processed, the present trend is to install Silo type of tanks of capacity as large as 1,00,000 liters each. This will reduce the cost of building, capital cost of tanks as well as operation, cleaning and maintenance costs, since the number of unit required for any desired capacity is considerably few. The total capacity of raw milk storage tanks will be, under normal circumstances, equal to daily intake at the plant. With a coordinated programme of rate and time of receiving at the plant, and the rate of processing, some raw milk storage capacity could be reduced.Storage facilities at intermediate stages of processing such as for manufacturing operations like separation, standardization, clarification, products manufacturing as ice-creams, butter, cheese, evaporated milk, milk powder, etc. have to be studied for each stage independently. While deciding on the number and size of tanks, for each facility, the length of storage time as well as the time required to clean and sterilize the tank before the next filling starts, has to be taken into consideration.Installing standard sizes, storage for different products, helps in flexibility with respect to alternative use and future expansion. The horizontal or the vertical design consideration must include economy of construction and housing, suitability and space availability.
Material of Construction: The material of construction of the storage equipment and road/rail milk tankers should conform to IS:739-1965. All product contact surfaces must be made of non-corrosive & non-reactive materials such as stainless steel (SS-304 or 316 grades) or aluminum or its suitable alloys. Other parts not coming in the direct contact must be decided based on requirements like appearance,heat transfer properties, strength and surrounding environment. Suitable fittings like ladder (internal and external) for inspection and cleaning should be provided. Suitable provision for milk inlet and out-let along with looking glass or manhole for manual cleaning or maintenance should be considered. The appropriate quality of gasket also needs considerations. The internal ladder could be made of stainless steel. The road /rail milk tankers must have provision of enclosures and locking of valves to prevent theft or sabotage.
Design Considerations: There has been in recent years, an increasing change away from open vats or vats with lids to closed cylindrical tanks. Vats previously in general use, which were rectangular, round or oval, are today used only in some instances such as in milk reception and more commonly in the cheese manufacturing plants. Cylindrical tanks are used either in an upright position or horizontally depending upon the space available. To compensate for irregularities in the floor, when tanks are erected, they are fitted with adjustable legs with levelling screws.
Today tanks, vessels or vats are made almost invariably of stainless steel. Aluminium has largely been replaced in the vessel construction industry. To be suitable for use in the dairy industry, the surfaces of vessels which are in contact with product must be smooth and, the welds in particular have to be made flush and polished during manufacture. Sharp angles where bases and sides meet in flanges and pipe inlets must be avoided. In vessels, corners which connot be properly cleaned must also be avoided. The specific design considerations for cans, tanks and tankers have been discussed below:
Milk can: The centre of gravity of full cans should be conveniently placed. It should be made rollable. The angles of shoulders of the can should allow quick and easy drainage of contents and provide enough strength along with ease of cleaning and inspection. The can should be fitted with handles to assist easy handling by workers. The neck width should allow good stability to hold it up-right in inverted position. Therefore, the design consideration should have angle of balance when upright of 30 degree, spill point greater than 30 degree, shoulder angle 45 degree and angle of balance when inverted 15 to 20 degree with respect to vertical surface.
Storage tanks/vessels: Inner shell is usually made of stainless steel or aluminium alloys with all welded points conforming to IS:2812-1964. Joints are well dressed and ground, smooth and free from visible porosity and brittleness. All inside surfaces are made to drain directly to outlet nozzle. Bottom slope is 1 in 15 to horizontal for vertical tanks and 1 in 12 for horizontal tanks, both in the longitudinal and transverse directions. Internal corners should have a radius of not less than 25 mm. Thickness of plate for shell wall and bottom plate vary according to size of tank and its capacity. A minimum 2 mm thickness for shell and 5 mm thickness for bottom plate is considered for lowest capacity tank/vat.Jacketed space surrounds the inner shell and used for circulation of steam, hot water, chiller water, brine or direct expansion refrigerant for heating in case of vats and for cooling as well as for maintenance of low temperatures of products in storage.
Insulation layer surrounds the inner vessel for ordinary vessels that are not refrigerated or surrounds the outer wall of jacketed space and is provided by vapour barrier on the outer surface. Outer shell surrounds the insulation layer. The material of this shell may be stainless steel, aluminium, galvanized iron or mild steel of not less than 3 mm thickness provided with vent hole to drain any condensation of moisture inside.
Road/Rail Tankers: These are made with or without compartments to transport different quality milk and also reduce churning and foaming during transportation.Maximum number of compartment per tanker is three. If a tank is made with compartments, the baffles require special care in installation and routine cleaning.Inner vessel of stainless steel of not less than 2 mm and outer shell of mild steel of not less than 3 mm thickness is considered in normal design.
Capacity Determination: Capacity of a storage tank is the volume of milk holding when filled to a level of 60 mm below top edge of inner vessel. Determination of capacity of a storage tank is dependent upon the products to be processed and milk operation procedure. This facilitates continuous processing of product, once the operation starts. Adequate storage facilities help independence of unloading of tankers from processing of milk.
iii. Parts of Storage Tank
Lid or manhole: Usually located at top or side portion of tank. In case of over head tank, manhole is located at the front end (in-side the process room). In silos,it is positioned near the bottom at suitable working height or at top. Usually the manholes are made of minimum 400 mm diameter, round or rectangular in shape and fitted with gasket around rim.
Product inlet: Inlet provision is made for pouring /loading the product through a bend from top of tank to the side so that milk will gently flow down the sidewall.In vertical silos inlet is given at the bottom to prevent foaming and air incorporation.
Product outlet: Outlet is fitted at the lowest point of bottom and installed to flush and provide proper drainage of product from the tank. In vertical silos, inlet also serves as outlet. Flanges type openings of minimum 50 mm diameter with bend of at-least 55 mm radius are considered most suitable.
Indicating thermometer: Pocket for indicating thermometer of range upto 40°C is provided at least 15 cm above the bottom of inner shell. Remote indicating and automatic temperature control and recording system may be installed for large size tanks and vats.
Opening: An opening is provided at the top of tank for chemical cleaning device of minimum 38 mm size.
Air vent: Air vent at top of tank is provided with screen to prevent entry of foreign materials and of sufficient size to prevent build up of pressure during filling and vacuum condition during rapid draining.
Agitator: Mechanical or pneumatic type agitator devices are provided to prevent cream-line formation during holding. It improves cooling efficiency and maintains uniform temperature and composition. It may be mounted on the lid of the tank near the manhole to facilitate dismantling for cleaning and inspection. Mechanical agitation device consists of motor driven agitator made of stainless steel, whereas pneumatic type has devices for introducing pressurized, clean and moisture/ oil free air into the silo.
Sight and light glass: One each with clear glass and diameter of not less than 100 mm is provided, effectively sealed to prevent ingress of foreign materials from the surroundings. These are shaped and mounted in such a way that inner surfaces drain inversely and is easily removable for cleaning and inspection. Each of these is mounted on opposite ends of top cover.
Sampling cock: size 50 or 63.5 mm
Measuring scale or dip-stick: Made of stainless steel and graduated to tank volume.
Ladder: Ladder, made of stainless steel or aluminum, is used inside and/or outside.It could be made of mild steel for external use.
High and low level cutoff: Large tanks are provided for automatic stoppage of pump motor, together with alarm bells and indicating lamps at the control panel to prevent accidental over filling or low level at outlet and consequent damage to pump material due to dry running.Like storage tanks, the Road/Rail tankers also have provisions of lid or man-hole, vent, inlet connection and ladder for their specific purposes. Outlet is provided at the rear end of a road tanker, whereas in rail tanker it is at the centre of compartment.
Each compartment may have separate outlet. The tanker alignment has sloping towards the outlet point for easy drainage of content. The outlet is provided with two way valve and its size is normally 63.5mm. Preferably flanged on tank end and union connection on the outlet end for hose connection is provided. Other special fittings include:
- Housing for valve: Stainless steel box with locking arrangement is provided for the safety during transportation.
- Rear Cabinet: Provision of rear cabinet is made to accommodate milk pump,metering equipment, sampling cock, unloading device and emergency spares such as gaskets, etc.
iv. Cleaning and Sterilization
For effective cleaning and sterilizing, the quality of the construction, finish and installation of equipment is of primary importance. Places such as dead ends, bends,etc. must be dismantled and cleaned manually. It is to be ensured that cleaning/sanitizing solution is not trapped in the equipments and pipe lines. Specific methods for cleaning and sterilizing of storage equipments have been discussed below:
Cans: Immediately after emptying, milk cans are turned upside down on a conveyor or rack and transported through several treatment stages such as drain, pre-rinse,caustic rinse, hot water rinse, hot air drying /steam sterilization and cold air treatment.The liquids are jetted into the can from below. Empty cans are also cleaned manually, steam sterilized and allowed hot drying.
Tanks, vats and vessels: Small tanks and vats can be cleaned manually. After a pre-rinse with lukewarm water, manual cleaning by hand brushes is done. Since there is inadequate lighting and soiling matter removal is dependent on the judgement of individuals, manual cleaning is not so effective. The spray lance of 1m to 1.5m long is directed by hand to the appropriate places of cleaning.
With the development of automatic Cleaning-in-Place (CIP), efficient cleaning and sterilizing results are obtained even in large size vessels. Especially designed spray arms and nozzles (turbine or ball spray) are normally used to ensure uniform spraying of detergent and sanitizing solutions over the surface in programmed manner.
Road/Rail Tankers: In addition to the manual cleaning and sanitization of road/rail tankers, programmed C.I.P. with spray ball or rotating turbine type arrangement for each compartment is used. For 20,000 L tankers, two spray balls and for 40,000 L, four spray balls are provided.
Chilling Center
i. Purpose
When the producer has no possibility for any mode of primary cooling, the objective should be to deliver the milk in the shortest possible time to the processing plant or collection centre. If no cooling facilities exist at the centre, its main objective is to receive all the milk from producers as quickly as possible and transport it for processing to chilling centre. The chilling centre pools, accepts and weighs the supplies of the milk from different sources, and checks the condition and quality of milk supplies. Milk is chilled immediately and stored till supplied it to the market or processor. So wherever, there is no possibility of raw milk to reach processing plant within 4 hours of production, a chilling centre is required to be established to save the milk from deterioration. This requires enforced time schedules for receiving milk at the primary collection point and a reliable delivery system to the market,processor or chilling centre. Where milk is to be mechanically cooled prior to further transportation, the most important pre-condition is also time. The arrival of milk at the chilling centre should be short for the better milk quality.
Installation of chilling center is done with the following objectives:
- Accepting, weighing and pooling the supplies of milk.
- Preserving the quality of raw milk supplies.
- Providing easy transport of chilled milk to the processor.
ii. Criteria for Selection of Site and Location
Selection of a suitable site and location for establishing a milk chilling centre is guided by:
- Location of main dairy or market,
- Within area of adequate milk production,
- Availability of adequate potable water supply,
- Sufficient electric supply,
- Proximity to a good road and/or railway station.
- Facilities of waste/sewage disposal, and
- Easy availability of human resources and infrastructural facilities.
iii. Operational Procedure
Essentially, this is the same as in a small dairy. On arrival, the milk is graded for acceptance/rejection, weighed, recorded, sampled for testing, cooled and stored at low temperature until dispatched to the market or processor.
Reception and Receiving Devices: Normally, milk is brought in cans to the chilling units from milk collection centers by different modes of transportation. In some small chilling centres, milk is also received directly from the producers.Depending on quantum of milk received, sources of supplies, type of milk supply containers, etc. receiving procedures and devices are provided at the reception
dock.
Chilling and Storage: As soon as the milk is received and dumped, it is pumped to storage tank through a chiller. The chilling system, that enables rapid cooling to reduce temperature to the desired level, is preferred. An ice bank system, using chilled water circulating through a plate heat exchanger to cool the milk immediately after reception, is more effective than immersing cans in chilled water, placing in a cold storage or cooling in jacketed vat with chilled water etc. The milk should be kept cold until it is despatched to processing plant. For this purpose, insulated bulk storage tanks mounted with motor-agitator and cooled by chilled water or refrigerant are the most effective.
Dispatch of Milk to Main Dairy: Once the milk is chilled, it is stored chilled in storage tank at the chilling centre till despatched to the main dairy. The chilled milk is drawn from the storage tank and filled either in cans or in road/rail milk tankers and, despatched. Before filling, each can and/or road/rail milk tanker is inspected carefully for cleaning and sanitization. Then, proper filling is ensured reducing loading and unloading time. The following steps are observed to ensure satisfactory despatch by tanker:
- The level of milk and recorded temperature are noted.
- Working of agitator is ensured.
- The milk delivery line is connected from the tank to the milk pump in the tanker through the flow meter. Wherever flow meters are not provided, the quantity of milk dispatched is ascertained by tele-gauges or dipstick.
- The outlet valve of the storage tank is opened, the milk pump is started and the milk is released into the tanker.
- The rate of flow using any of the devices is recorded when the flow has become steady.
- Milk is allowed to flow in the tanker to the prefixed optimum level, taking care to avoid excessive foam due to sudden rush of milk in the tanker compartments.
- Milk pump is stopped, the tanker covers are closed and secured by locking them.
- The milk delivery valve of storage tank is closed.
- After the operation, all connected milk delivery line is dismantled, sanitized and kept ready for next day use.
- A sample of milk is drawn and analyzed. Result is also recorded in the dispatch challan along with other information.
- The number of cans and quantity of milk kept in cold storage for dispatch are checked.
- If the milk is held in a storage tank, the necessary pipe line is connected and cans are filled.
- A composite sample is drawn as per the laid down procedure, analyzed and recorded.
- Satisfactory sealing of individual can is ensured to prevent tampering.
- Wherever, ice-cooled cans are used, the recommended precautions are observed.
Sampling and Testing of milk: At a chilling centre, milk is to be sampled at 3 stages:
- At milk reception dock for acceptance/rejection of milk and making payment to individual suppliers.
- After bulking and chilling of milk kept in storage tank/vat and /or milk cans for record and verification.
- At the time of dispatch to verify the quality of milk with the record of the receiving dairy.
Quality of milk on the reception dock is assessed by performing the platform tests.Further, milk samples are analyzed in the laboratory for chemical and microbiological quality of all accepted milk for making payments, maintaining records etc.
Chilling of Milk
i. Importance
Milk leaves the udder at body temperature containing only a few microorganisms.The number increases rapidly at this temperature, if growth is not checked immediately by chilling the milk. Chilling is necessary after receiving milk at collection/chilling center. Chilled milk can easily and safely be transported without having appreciable deteriorative changes due to microbial growth. Thus, raw milk is chilled to a) limit the growth of bacteria, b) minimize micro-induced changes, and c)maximize its shelf life. However, chilling of milk involves additional expense which increases the cost of processing. Importantly, chilling process does not kill microorganisms nor it renders milk safe for human consumption. It is only a means of checking the growth of microorganisms for a certain period.
ii. Effect on Microbial Growth
Generally, milk is cooled immediately after milking to below 10°C. within 4 hours to prevent/retard the multiplication of thermophilic and mesophilic bacteria including disease producing and food poisoning organisms until the milk reaches the dairy.The extent of control of growth of microorganisms is dependent on type of organisms.Staphylococci do not grow below 10°C. Growth stops for most types of B. coli,B. proteus and Micrococci between 0°C and 5°C. If milk is stored cold for too long time, there can be an undesirable increase in psychrotrophic organisms which produce extremely heat resistant lipases and proteases.
The time factor is critical in arresting bacterial growth in fresh milk. As milk from the udder of healthy cows has a low bacterial count. There is a lag phase immediately after milking, for around 4 hours, before bacterial multiplication begins to grow. The quicker milk is cooled, the better the quality and in the ideal condition, milk is cooled immediately after milking to 40C or below and held at that temperature till it is processed. The effect of storage temperature on microbial growth in raw milk is shown in below Table.
The time factor is critical in arresting bacterial growth in fresh milk. As milk from the udder of healthy cows has a low bacterial count. There is a lag phase immediately after milking, for around 4 hours, before bacterial multiplication begins to grow. The quicker milk is cooled, the better the quality and in the ideal condition, milk is cooled immediately after milking to 40C or below and held at that temperature till it is processed. The effect of storage temperature on microbial growth in raw milk is shown in below Table.
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| Effect of storage temperature on microbial growth in milk |
iii. Effect on Keeping Quality of Milk
Fresh raw milk is cooled to 40C to extend its shelf-life (freshness). At this temperature, the activity of enzymes, the growth of microorganisms and metabolic processes are all slowed down. As a result, prolonged holding of chilled milk is bound to cause significant deteriorative alterations in keeping quality of milk. In addition, cooling causes a considerable dissociation of b-casein, calcium and phosphate ions and proteases from the casein micelles. The milk loses its suitability for cheese making, coagulation times are increased and the curd tension of the coagulum is less.
Chemical and biochemical processes are considerably slowed down by cooling.However, milk, which has been stored, sometime has a bitter off-flavour. Enzymes and microorganisms can cause chemical changes which are accompanied by a lower pH value and change in nitrogen-containing compounds. Psychrophilic microorganisms cause proteolysis of casein and, together with enzymes, also that of albumin. Protein breakdown products (polypeptides) are formed. Certain bacteria are responsible for the hydrolysis of fats causing rancid flavour development.Several enzymes such as oxidase, catalase and reductase are active for a long time, even at 0° C. Hence, if the time between milk reception and processing is 2 to 3 days, the storage temperature should be kept between 2° C to 5° C for minimum effect on keeping quality of milk.
iv. Effect on Physico-chemical Properties of Milk
The effect of rapid cooling and storage at low temperatures on the physico-chemical properties of the milk components are being discussed below:
- Failure to rennet/acid coagulation: The failure of casein to coagulate at 2°C either at pH 4.7 or after rennet treatment has been utilized in the development of continuous cheese making process, where the milk is either acidified or renneted at 2°C and the temperature is subsequently raised to about 15.6°C or 30°C to effect coagulation.
- Failure to coagulate at isoelectric point: Milk fails to coagulate at 2° C after adjusting to the isoelectric point (pH) of casein. At 2-3° C there is an increase in the diffusible inorganic salts and a change in the casein micelle structure. Some micellar casein is converted to a non-micellar or soluble form(e.g. b-casein). At 2°C, the pH of the milk has to be reduced to 4.3 to effect complete casein coagulation, whereas at 30°C the recovery of the casein at pH 4.6 was nearly complete. Also the properties of casein obtained by acid precipitation at 2° C and pH 4.3, and at 30°C and pH 4.6 were found slightly different.
- Increase in viscosity: Storage of milk at 20 to 5°C, both raw and pasteurized caused an increase in the viscosity of the product which may be related to changes in the protein system, since viscosity is influenced largely by the colloidal components of milk. Probably, conversion of colloidal calcium partly to soluble form may uncoil the casein micelle. The change in viscosity with storage at low temperature (2 to 5°C) was greatest during the first 24 hours and reaches maximum after about 72 hours.
- Decrease in cheese curd firmness: The cold aging of milk increased the rennet coagulation time at 30°C. The increased coagulation time was inversely related to the ratio of colloidal calcium-phosphate, and could be reversed by heating to 40°C for 10 minutes or by addition of calcium chloride to the milk prior to cold aging.
- Increased hydrolytic rancidity: Cold storage of milk below 7°C is associated with an increase in the rate of development of rancidity. Cooling tends to dissociate the casein micelle and increases the total available lipase in the milk system. Subsequent treatment to milk (warming, agitation, etc.) bring lipases into contact with fat globules and liberate free fatty acids to produce rancidity in milk.
- Increased Foaming: Cold milk foams readily. Milk proteins concentrate in the lamellae of the foam where b-lactoglobulin acts as a surface active agent.Foams are formed by the preferential adsorption of surface active materials at an air-liquid interface with orientation of the material to form an air bubble.
- Physical structure of fat globules: Crystal structure and size vary as a function of both cooling rate and cooling temperature and regulate the hardness of the milkfat. More fat passes into the solid state by direct cooling than by stepwise cooling. The sensitivity of the fat globule membrane to shear and subsequent release of free fat is greater in milk that has a higher proportion of solid to liquid fat. Thus, milk rapidly cooled, 0-5°C, is more sensitive to shear damage than that is cooled more slowly and in a stepwise manner.
i) Increased clustering of fat: When milk is stored at low temperature (0-5°C),change in the surface characteristic of fat globule membrane results in more rapid creaming due to increased fat globule clustering effected by concentration of “agglutinin” on the fat globule surface.
ii) Migration of substances: Cooling milk to 4°C leads to migration of some membrane proteins, phospholipids, xanthin oxidase, natural copper, etc. from fat globule membrane to milk plasma.
v. Equipment and Methods of Chilling
Cooling is the predominant method of maintaining milk quality during collection. The most important factor next to hygienic production of milk is the time between completion of milking and reducing the temperature low enough to restrict bacterial growth. Whatever the method of cooling, the faster the temperature is reduced from 37°C at milking, the better will be the resultant milk quality.Selection of a suitable method and equipment for prompt cooling i.e. chilling milk is dependent upon the available facilities at the moment keeping in view the volume of milk handling and time for cooling and keeping it cold till reaches for processing. Various methods of cooling of milk are described below:
- Can (container) Immersion: The fresh milk immediately after milking, is placed in a container (preferably metal) which is gently lowered into a tank/trough of cooling water. Cooling of milk will slowly take place and if the water is cold enough, the milk temperature will be reduced low enough to allow the milk to be marketed/processed. The milk inside the cans may be stirred with the help of plunger for uniform quick cooling.
- Surface Cooler: An improvement of water cooling is a metal surface cooler,where water flows through the inner side and milk flows over the outer surface in a thin layer. A well designed water cooler will reduce milk temperature almost instantaneously. The cooled milk is received below in a receiving trough, from which it is discharged by gravity or a pump.
- Plate Heat Exchanger: This is the most widely used very effective equipment for chilling of milk by the commercial dairy plants. Several stainless steel plates are mounted on a solid stainless steel frame in which the milk to be chilled and chilling water flow alternatively and counter-currently. The number and size of plates in the exchanger depend upon the capacity of the plant which may vary as per requirement. This method of chilling is more efficient, more hygienic, involves less manual labour and cost effective.
- Tubular Cooler: This consists of two concentric tubes, inner tube usually carries the milk to be chilled while cold water is passing through the hollow space in between the pipes. The length and diameter of both the tubes are determined according to the capacity of the plant. The flow of the milk and chilled water is in opposite direction, i.e. counter-current. The tubular cooler is efficient,, where milk is not exposed to atmosphere.
- Bulk Milk Coolers: These consist of a double jacketed vat fitted with a mechanical agitator. It also has provision for circulation of chilled water which comes from the chilled water tank. Normally, milk is chilled and subsequently stored at low temperature until transported to processing units for further processing. Bulk milk coolers are generally installed at chilling centres.
- Rotor Freeze: Rotor freeze provides spray of chilled water outside the cans obtained by mechanical refrigeration system and passing through the perforated tubes around the neck of the can. With this system, milk temperature is brought down to 10°C from 35°C within 15 minutes.
Brine Cooling: The direct expansion coil is used to cool brine which is then circulated by a pump around the product to be cooled. Brine system of cooling may be of a) brine circulating type, b) brine storage type, and c) congealing-tank type.This system has the advantages of being safe with ammonia and of causing less damage in case of a leakage and the temperature can be easily controlled. It also allows the storing up of refrigeration in the cold brine and therefore, allows heavy refrigerating loads of short duration to be carried with a system having a much smaller compressor than direct expansion system used. The overall thermal efficiency of a brine system is usually less than the direct expansion system on account of the one extra heat transfer and the added radiation losses.
Ice Cooling: Ice, produced by commercial ice plants, is used in some countries to cool milk. The use of ice for cooling is generally fairly expensive and not particularly effective due to the problems in getting an optimum and rapid heat transfer from the liquid milk to the solid ice. Different methods of cooling milk by ice are:
- In Can Cooling: In this method, ice is placed in a metal container, known as ice gum or ice cone, which is inserted into the can of milk. This permits a more effective heat exchange rate by giving off latent heat of ice and sensible heat of melted water but reduces the volume of milk that can be carried in the milk can. When ice is completely melted in the ice cone and there is no more heat transfer, the water is thrown and fresh ice pieces are put in. The process of cooling milk by this method continues even during transportation from collection centres to processing unit.
- Direct Addition of Ice: Sometimes cooling of milk is done by direct putting ice into the milk. While this achieves an effective transfer of energy, and reasonably rapid cooling, it has a major disadvantage of diluting the milk with water, which will require removal at subsequent processing or the sale of adulterated milk.
- Mechanical Cooling: Mechanical refrigeration system is the most effective means of arresting bacterial growth by lowering milk temperature to around 40C. This system of cooling can be utilized in the following manners:
- Household Refrigerator: This is a practical method for small volume of milk(say from 1 or 2 animals, approx. 5 litres) where the farmers has a refrigerator.The milk in metal container immediately after milking, is placed in a domestic household refrigerator where the milk will slowly cool to the temperature of the refrigerator.
- Surface/Immersion Cooler: Under direct expansion system, a mechanical refrigerator compressor and condenser (usually air cooled) produces a liquid refrigerant (freon or ammonia) which when passing through an expansion system causes a rapid reduction in temperature.
- Expansion Bulk Tank: Direct expansion bulk tank, ranging in size from 500 L to 20,000 L, is an energy efficient system of cooling the milk to 40 C within the acceptable period of 4 hours. It is used directly on farms where, medium to large sized herds are milked or at collection/chilling centre.
- Putting Ice Around Metal Cans of Milk: It is the simplest form of cooling milk in which ice slabs are stacked around the metal cans of milk on the delivery vehicle and the system relies on heat transfer by contact.
- Ice Bank: The ice bank is a widely used for fast cooling of milk. This method of cooling reduces the size of the refrigeration compressor (hence, power requirement) by building up a reserve of ice over a long period. In ice bank,cooling is done through a plate heat exchanger or a surface type cooler with chilled water being the cooling medium. The chilled water is pumped from the ice bank through the heat exchanger and back to the ice bank. Ice banks have considerable flexibility in size and range from a small, self-contained portable unit to a large, using a multiple ammonia compressors, water condensers and associated cooling towers.
Milk Chilling and Storage
Production of milk in India is very widely scattered in rural areas and at vast distances from the places of consumption i.e. urban areas. Various sources which contribute to the micro-flora in milk are containers, udder of the animal, dust and dirt particles, fodder, leaves, atmospheric air, the milker and the animal itself. The number further increases during handling, storage, transportation, processing and consuming practices prevalent in rural areas. The number and types of micro-organisms would depend upon the conditions and the sources of contamination.
As soon as microorganisms get into milk, they start growing rapidly because milkcontains all the nutrients and favourable conditions required for their growth. If the growth of micro-organisms is not checked, then their growth will continue and several bio-chemical changes will take place affecting the quality of milk. Further,if milk has to be transported to longer distances, considerable time is involved between production and processing. During this period, milk must be protected from spoilage by the action of micro-organisms. Prompt cooling, i.e. chilling is one of the methods of preserving milk, after production to maintain its quality.
As soon as microorganisms get into milk, they start growing rapidly because milkcontains all the nutrients and favourable conditions required for their growth. If the growth of micro-organisms is not checked, then their growth will continue and several bio-chemical changes will take place affecting the quality of milk. Further,if milk has to be transported to longer distances, considerable time is involved between production and processing. During this period, milk must be protected from spoilage by the action of micro-organisms. Prompt cooling, i.e. chilling is one of the methods of preserving milk, after production to maintain its quality.
Let Us Sum Up
As soon as milk arrives at the reception dock, it must be received after thorough checking of the quality for freshness and composition. The layout and design of the dock and equipment should facilitate the reception. Size, shape, capacity and inter-spacing of receiving devices must speed up to complete the reception within 2-3 hours. The conveyor should be long enough so that by the time can reaches to tilting device, the operator must be able to decide for acceptance or rejection of milk after performing the platform tests. Accepted milk must be weighed, recorded,sampled and dumped. Empty cans and tankers should be washed and sanitized and returned to the suppliers.
Cleaning and sanitization of Milk Cans and Tankers
Cleaning is done to remove the residues of milk from the surface of the utensils,while sanitization is done to destroy all types of micro-organisms present on the surface of the utensils and equipments.
i. Types of Washers:
The types of washers include manual washing, mechanical washing and cleaning-in place.
(i) Manual washing: Small plants are not equipped with mechanical can washers and employ manual washing methods. Manual washing can be aided by installation of can washing trough, can scrubber, and can rinsing and steaming block. These tools will be helpful in reducing the manual brushing, rinsing and sanitizing the cans.
(ii) Mechanical washer: In mechanical washing, the can is usually passed over a succession of jets emitting water, cleaning solution, hot water, steam and air. Where the operation is big and manual washing is considered difficult and uneconomical, washing is done mechanically. Mechanical can washers are of two types:
a) Rotary type: One man is required to place the cans and lids in inverted position in the machine and remove them after washing and drying. The can and lid are moved through a rotating platform divided into sections.A series of tanks of solutions are located under the platform. Cans get continuous spray of various solutions both inside and outside through circulating pumps and solutions return to respective tanks. The rotary washer rotates at intervals.
b) Straight through or tunnel type: In this type, empty can and lid in inverted position enter into the tunnel at one end of the conveyor and come out at the other end after getting cleaned, rinsed, sterilized and dried in straight-up position. The main operations involved are: pre-rinsing with clean water, steam sterilization, detergent solution washing,hot water rinsing and hot air drying. All these operations are carried out in quick succession and the process is continuous.
(iii)Cleaning-in-place: The permanent line as well as equipment remain intact during the cleaning and sterilizing procedures. Milk tankers can be cleaned by this method. The modern dairies are equipped with CIP system of cleaning which is controlled by electronic device. The cleaning operations are programmed according to the need and the operations have to make necessary connection for the proper flow of liquids. The CIP system consists of essentially 3 tanks, namely cold water, hot water and detergent or lye tank, and an automatic electronically controlled panel. The route sequence selection may be manual, semi or fully automatic. The sequences are programmed operations controlled by card, tape or microprocessor.
ii. Sanitizing Systems
Cleaning is followed by sanitizing. Sanitizing is done chemically or by hot water or steam to kill pathogenic organisms and nearly all non-pathogenic organisms. Dairy equipment can be sanitized with application of one of the following methods:
- Flushing: All equipment and piping are assembled and flushed out with a hypochlorite solution.
- Spraying and brushing of equipment.
- Fogging: sanitizing solutions may also be applied by air pressure or atomizing solution in form of a mist or fog. The minimum chlorine strength should be 400 ppm and the strength at the discharge end around 100 ppm. To avoid corrosion,the chlorine should not stand in the tank longer than 30 minutes.
- Submersion: Small parts, pails and certain utensils may best be sanitized by submersion in a sanitizing solution.
Laboratory Testing of Milk Samples
For conducting some other tests to assess the freshness, hygiene and composition of milk, small laboratories and well trained technicians are needed. These tests are also needed to improve the quality of milk production and supply. Milk of initial good quality alone will give products of better quality. Moreover, the payment for milk is based on its constituents such as fat and solids-not-fat (SNF) contents. These tests are conducted in the laboratory.
i. Chemical Tests
Various chemical and physical tests conducted to assess the quality of milk received in a dairy include titratable acidity, fat content, total solids and solids-not-fat content,and tests for detection of adulterants.
Titratable Acidity: Acidity of milk is expressed in term of its lactic acid content.10 to 50 ml of milk sample is titrated with N/9 or N/10 NaOH solution and phenolphthalein as indicator. Normal acidity of fresh milk varies between 0.10 to 0.16 % lactic acid. The titratable acidity (T.A.) as lactic acid per 100 ml of milk is calculated by using formulae as under:
% Lactic acid = 9 * V1 * N1 / V2
where, V1 = Volume of standard NaOH solution, ml
N1 = Normality of standard NaOH solution
V2 = Volume of milk sample taken, ml
Fat Test: Fat test of milk is done for making payment of the milk. Among several methods, one common method is the acidobutyrometric butterfat test or Gerber test. Fat globule membranes and proteins of the milk are hydrolyzed with concentrated sulphuric acid to break the emulsion and to set the fat free. The volume of fat from a given quantity of milk sample is measured in a specially designed glass recipient, known as butyrometer. The butyrometer reading gives the result directly in fat percentage. For accurate results, the reading has to be taken quickly to avoid cooling of the fat column.
Now, Milko-tester Minor or semi-automatic butterfat analyzer is used for determining the fat content in milk. This is based on the principle of scattering of light by milk fat globules. Light transmission through the milk-mix is measured photometrically and read directly as the fat percentage in milk samples on digital display. Accuracy of the result is approximately the same as for the Gerber fat test.
Determination of total solids (TS) and Solids-not-fat (SNF) content: A lactometer is used to measure the specific gravity of milk. Based on the lactometer reading of milk taken under standard conditions and knowing the fat percentage as determined by the Gerber method, it is possible to calculate TS and SNF by using the well known Richmond’s formula which differs for the types of lactometer, viz. Quevenne, Zeal-and BIS-lactometer.
(i) Quevenne lactometer:
% TS = CLR/4 + 1.2 F + 0.14
% SNF= CLR/4+0.2 F + 0.14
(ii) Zeal lactometer
% TS = CLR/4 + 1.2 F + 0.50
% SNF= CLR/4+0.2 F + 0.50
(iii) BIS lactometer
% TS = CLR/4 + 1.2 F + 0.60
% SNF= CLR/4+0.2 F + 0.60
Where, CLR = corrected lactometer readings, obtained by applying the specific correction factor to the observed lactometer readings based on temperature of milk.
Determination of TS and SNF of milk can help to detect the adulteration of milk.TS and SNF also form the basis for the pricing of milk.
(i) Quevenne lactometer:
% TS = CLR/4 + 1.2 F + 0.14
% SNF= CLR/4+0.2 F + 0.14
(ii) Zeal lactometer
% TS = CLR/4 + 1.2 F + 0.50
% SNF= CLR/4+0.2 F + 0.50
(iii) BIS lactometer
% TS = CLR/4 + 1.2 F + 0.60
% SNF= CLR/4+0.2 F + 0.60
Where, CLR = corrected lactometer readings, obtained by applying the specific correction factor to the observed lactometer readings based on temperature of milk.
Determination of TS and SNF of milk can help to detect the adulteration of milk.TS and SNF also form the basis for the pricing of milk.
ii. Microbiological Tests
Microbiological tests provide information on the sanitary condition and keeping quality of milk. The tests are intended to be carried out on samples collected for microbiological analysis. Microbiological standards for cow milk have been presented in below Table.
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| Microbiological Standards for Cow Milk |
Methylene blue and Resazurin reduction tests measure the bio-chemical activity of microorganisms in milk. They get reduced, if added to milk, after a certain time and lose their colour. Quick reduction of a given quantity of dye means high microbiological activity and vice versa.
Half-hour methylene blue reduction (MBR) test: The length of time taken by milk to de-colourize methylene blue is a fairly good measure of its bacterial content.Ten ml milk in sterile test tube is well mixed with one ml methylene blue solution.Tube is closed with sterile rubber stopper and incubated in a water bath maintained at 37.5 + 0.5oC. Tube is inspected after 30 minutes and seen whether milk in the tube is de-colourized at least up to within 5 mm of the surface. Milk is graded as in above Table.
Ten-Minute resazurin test: Since resazurin reduction occurs in two stages, the first from blue to pink, and the second from pink to colourless, the quality of milk can be assessed easily in shorter time. Procedure is the same as described in MBR test. At the end of 10 minutes + 30 second of incubation, the tube is removed from the water bath and immediately the colour is matched with the resazurin disc in the comarator. The result shall be interpreted as follows:
Half-hour methylene blue reduction (MBR) test: The length of time taken by milk to de-colourize methylene blue is a fairly good measure of its bacterial content.Ten ml milk in sterile test tube is well mixed with one ml methylene blue solution.Tube is closed with sterile rubber stopper and incubated in a water bath maintained at 37.5 + 0.5oC. Tube is inspected after 30 minutes and seen whether milk in the tube is de-colourized at least up to within 5 mm of the surface. Milk is graded as in above Table.
Ten-Minute resazurin test: Since resazurin reduction occurs in two stages, the first from blue to pink, and the second from pink to colourless, the quality of milk can be assessed easily in shorter time. Procedure is the same as described in MBR test. At the end of 10 minutes + 30 second of incubation, the tube is removed from the water bath and immediately the colour is matched with the resazurin disc in the comarator. The result shall be interpreted as follows:
Direct Microscopic Count (DMC): The direct microscopic count method consists of examination of milk under a compound microscope. It enables the rapid estimation of the total bacterial population of a sample of milk and also reveals useful information for tracing the source of contamination in milk.
Reception of Milk
Reception includes following operations: Unloading, grading, conveying, sampling,testing, weighing or measuring and recording, dumping and pumping.
i. Unloading
Milk brought either in cans or in tankers is unloaded.
Milk cans: As soon as vehicle carrying milk in cans arrives at the reception dock,the cans are unloaded manually and generally placed on the conveyors. If the level of the truck surface is in line with the platform, the unloading of cans requires least
effort.
Road/Rail tankers: Tanker, after grading and sampling, is connected with the pump and piping and milk is pumped through a flow meter where the volume of milk is automatically recorded.
ii. Conveying
Milk cans are placed on gravity roller or power chain conveyor. The lids are removed and each can is subjected to rapid sensory evaluation and some preliminary tests to decide the acceptance or rejection of the milk.
Conveyors: Conveying systems and related devices must be considered in connection with efficient materials handling to provide direct and continuous flow from a point of origin to the ultimate destination. The conveyor system should be simple, direct,flexible, and free from trouble spots. It should have proper elevation at all points,and easy to clean, lubricate and maintain. Sharp curves, sudden changes of elevation switching of various size packages and other tasks can be handled without difficulty.
Pipelines: In a milk plant, liquids are conveyed from point to point by means of pipes that are joined together and attached to equipment by sanitary pipe fittings.Special metals are needed for the construction of pipe fittings coming in contact with dairy products in order to protect flavour and purity. Stainless steel sanitary pipe is now used throughout the industry. The size, length and joints of piping must be optimized in light of quantity of product to be pumped to desired destination in a given period of time.
Conveyors: Conveying systems and related devices must be considered in connection with efficient materials handling to provide direct and continuous flow from a point of origin to the ultimate destination. The conveyor system should be simple, direct,flexible, and free from trouble spots. It should have proper elevation at all points,and easy to clean, lubricate and maintain. Sharp curves, sudden changes of elevation switching of various size packages and other tasks can be handled without difficulty.
Pipelines: In a milk plant, liquids are conveyed from point to point by means of pipes that are joined together and attached to equipment by sanitary pipe fittings.Special metals are needed for the construction of pipe fittings coming in contact with dairy products in order to protect flavour and purity. Stainless steel sanitary pipe is now used throughout the industry. The size, length and joints of piping must be optimized in light of quantity of product to be pumped to desired destination in a given period of time.
iii. Examination of Raw Milk
Raw milk has to pass through rigorous examination which may include organoleptic,physical and chemical tests to assess the quality of intake milk rapidly, and decide for its acceptance or rejection. All these tests known as “platform tests” are performed on each can/tanker to assess the quality of the incoming milk before it is accepted and weighed. These tests must be easy to perform, give quick and reliable results and should not require complicated and elaborate equipment. The classification of milk on the basis of quality is usually referred to “grading of milk”.So grading of milk is done on the basis of platform tests which include organoleptic
as well as preliminary tests.
Purpose: Milk received is further subjected to some sort of processing including heat processing for manufacturing products, and finally marketed to consumers. A good quality product cannot be made from bad quality raw ingredients. So, quality and composition of raw milk must be checked for freshness, hygiene and conformity to the legal standards. These can be accomplished by examination of raw milk through platform and other laboratory tests. Accordingly, the main purposes of examination of raw milk at reception dock are assessment of (i) freshness, (ii) hygienic quality, and (iii) composition.
Organoleptic tests: Organoleptic or sensory tests are performed with the help of five sensing organs, viz. eye, nose, tongue, ear and skin. The general appearnce,cleanliness, colour, taste and smell of milk are tested before emptying the transport containers.Milk in can is evaluated while moving on the conveyor. Organoleptic tests are quick, cheap and with growing experience of the assessor, very reliable. Since practically no equipment is needed, the sensory test can be carried out anywhere and anytime. However, sensory tests are subjective and would depend on the assessor’s faculty of perception.
Smell or odour: Just after opening the lid of the container, sniffing will detect the smell/odour of the milk. Normal milk should not have any off-or unnatural smell in it. If the smell is slightly sour, the milk might have undergone microbial deterioration.
Appearance: After the odour test, milk in each can is observed for any floating extraneous matters, off-colour, or partially churned milk. Normal milk should be free from these. Presence of visible dirt, straw or manure indicates that milk has been handled in an unhygienic way. The colour of milk of cows and sheep should be slightly yellowish-white, that of buffaloes and goat absolutely white. If the colour is reddish, the milk may contain blood; if it is yellowish, it may contain pus, such milk may be secreted from infected udder (mastitis) and should not be accepted.
Taste: Taste of milk can be noted by taking a spoonful milk in the mouth and rotating inside with the help of tongue. When doubt exists concerning smell, the taste of the milk may help to determine sourness and if so, milk should be rejected.Adulteration of milk with salt, sugar, etc. can also be detected by taste and found positive must be rejected.
Temperature: With practice, the grader can judge the temperature of milk with a high degree of accuracy by touching the container. Abnormal to the weather or condition may indicate the prehistory of milk with respect to its cooling or heating,etc.
Preliminary tests: Preliminary tests as discussed below. These are simple and rapid physical-chemical tests which can be performed easily on the reception dock:
Clot-On-Boiling (C.O.B.): A small portion of milk is heated to boiling point in a test tube for checking whether it withstands heat treatment without clotting. If the milk clots on boiling it is sour or abnormal. This milk cannot be processed any more and hence it should be rejected.Alcohol test: Milk with increased acidity or of abnormal salt balance or mastitis flocculates after addition of alcohol. This test is used to determine heat stability of milk. If no flocculation occurs after addition of alcohol, the milk is fresh or its acidity is only very slightly increased. If milk flocculates with alcohol, the milk is heat unstable and it should be rejected.
Titratable acidity (T.A.): The titratable acidity of milk is determined by titrating 10 ml of milk with N/9 NaOH solution to assess sourness in milk. The result is either expressed in degrees Dornic, i.e. ml of N/10 NaOH used being equal to 1 degree Dornic(Do) or in % lactic acid, whereby ml of N/10 NaOH used is equal to 0.01% w/v lactic acid. Milk testing more than 0.15% lactic acid should be rejected.
pH: The pH value can be measured with an electronic pH meter or with the help of different pH-indicators to assess the acidity of milk. Normal milk has pH ranging from 6.6 (in cow milk) to 6.8 (in buffalo milk). A higher pH (7.0 to 7.4) means milk from infected (mastitis) udders or it is neutralized by alkali. The major shortcoming of this method is its poor sensitivity since milk is extremely well buffered system,slight change in acidity or alkalinity cannot be detected.
Lactometer test: Lactometer is used for determination of specific gravity. However,test result obtained can be misleading due to variation in temperature and fat content in milk etc. This method is correct only when carried out at the correct temperature and combined with milkfat test.
Sediment test: The sediment test is used to check the visible foreign matter contained in the milk. Off the bottom sediment tester or barrel type sediment tester may be used. Test is carried out by allowing a measured quantity of milk (usually 500 ml) to pass through a fixed area of a filter disc and comparing the sediment left with the prepared standard (Table). Any hair flies, pieces of hay or straw or any large particles of dirt are not included in grading sediment. Presence of appreciable sediment indicates careless or insanitary dairy farm practice. However lack of sediment is not always indicative of ideal conditions, since visible sediment may be readily removed by straining at the dairy farm. It may have bacterial contamination.
Purpose: Milk received is further subjected to some sort of processing including heat processing for manufacturing products, and finally marketed to consumers. A good quality product cannot be made from bad quality raw ingredients. So, quality and composition of raw milk must be checked for freshness, hygiene and conformity to the legal standards. These can be accomplished by examination of raw milk through platform and other laboratory tests. Accordingly, the main purposes of examination of raw milk at reception dock are assessment of (i) freshness, (ii) hygienic quality, and (iii) composition.
Organoleptic tests: Organoleptic or sensory tests are performed with the help of five sensing organs, viz. eye, nose, tongue, ear and skin. The general appearnce,cleanliness, colour, taste and smell of milk are tested before emptying the transport containers.Milk in can is evaluated while moving on the conveyor. Organoleptic tests are quick, cheap and with growing experience of the assessor, very reliable. Since practically no equipment is needed, the sensory test can be carried out anywhere and anytime. However, sensory tests are subjective and would depend on the assessor’s faculty of perception.
Smell or odour: Just after opening the lid of the container, sniffing will detect the smell/odour of the milk. Normal milk should not have any off-or unnatural smell in it. If the smell is slightly sour, the milk might have undergone microbial deterioration.
Appearance: After the odour test, milk in each can is observed for any floating extraneous matters, off-colour, or partially churned milk. Normal milk should be free from these. Presence of visible dirt, straw or manure indicates that milk has been handled in an unhygienic way. The colour of milk of cows and sheep should be slightly yellowish-white, that of buffaloes and goat absolutely white. If the colour is reddish, the milk may contain blood; if it is yellowish, it may contain pus, such milk may be secreted from infected udder (mastitis) and should not be accepted.
Taste: Taste of milk can be noted by taking a spoonful milk in the mouth and rotating inside with the help of tongue. When doubt exists concerning smell, the taste of the milk may help to determine sourness and if so, milk should be rejected.Adulteration of milk with salt, sugar, etc. can also be detected by taste and found positive must be rejected.
Temperature: With practice, the grader can judge the temperature of milk with a high degree of accuracy by touching the container. Abnormal to the weather or condition may indicate the prehistory of milk with respect to its cooling or heating,etc.
Preliminary tests: Preliminary tests as discussed below. These are simple and rapid physical-chemical tests which can be performed easily on the reception dock:
Clot-On-Boiling (C.O.B.): A small portion of milk is heated to boiling point in a test tube for checking whether it withstands heat treatment without clotting. If the milk clots on boiling it is sour or abnormal. This milk cannot be processed any more and hence it should be rejected.Alcohol test: Milk with increased acidity or of abnormal salt balance or mastitis flocculates after addition of alcohol. This test is used to determine heat stability of milk. If no flocculation occurs after addition of alcohol, the milk is fresh or its acidity is only very slightly increased. If milk flocculates with alcohol, the milk is heat unstable and it should be rejected.
Titratable acidity (T.A.): The titratable acidity of milk is determined by titrating 10 ml of milk with N/9 NaOH solution to assess sourness in milk. The result is either expressed in degrees Dornic, i.e. ml of N/10 NaOH used being equal to 1 degree Dornic(Do) or in % lactic acid, whereby ml of N/10 NaOH used is equal to 0.01% w/v lactic acid. Milk testing more than 0.15% lactic acid should be rejected.
pH: The pH value can be measured with an electronic pH meter or with the help of different pH-indicators to assess the acidity of milk. Normal milk has pH ranging from 6.6 (in cow milk) to 6.8 (in buffalo milk). A higher pH (7.0 to 7.4) means milk from infected (mastitis) udders or it is neutralized by alkali. The major shortcoming of this method is its poor sensitivity since milk is extremely well buffered system,slight change in acidity or alkalinity cannot be detected.
Lactometer test: Lactometer is used for determination of specific gravity. However,test result obtained can be misleading due to variation in temperature and fat content in milk etc. This method is correct only when carried out at the correct temperature and combined with milkfat test.
Sediment test: The sediment test is used to check the visible foreign matter contained in the milk. Off the bottom sediment tester or barrel type sediment tester may be used. Test is carried out by allowing a measured quantity of milk (usually 500 ml) to pass through a fixed area of a filter disc and comparing the sediment left with the prepared standard (Table). Any hair flies, pieces of hay or straw or any large particles of dirt are not included in grading sediment. Presence of appreciable sediment indicates careless or insanitary dairy farm practice. However lack of sediment is not always indicative of ideal conditions, since visible sediment may be readily removed by straining at the dairy farm. It may have bacterial contamination.
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| Quality of Milk by Sediment Test |
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| Quality of Milk by Alizarin-Alcohol Test |
Alizarin-alcohol test: Incorporation of alizarin in alcohol helps
to determine both heat stability and approximate percentage of acidity
in milk. Milk showing poor heat stability is rejected.
iv. Tilting/Emptying of Milk Cans
Acceptable milk in cans are lifted manually from the conveyor, rested on floor mounted can tipping cross bar padded with rubber and tilted to drain the milk into weigh bowl. When the can tipping device is used, the operator must hold the can until the milk drains from it and then convey the emptied can by hand to the washer via drip saver. For quick, easy and high speed, a dump grid, suspended over the weigh tank, is used on which the can drains and is automatically moved to the can washer.
v. Weighing/Measuring and Recording of Milk
The milk in cans is dumped into the weigh tank/bowl, of single or double compartment,either manually or mechanically. The stainless steel weigh bowl of 250 or 500 Kg capacity is attached to a circular dial weigh scale and the portion towards the outlet valve overhangs with anti-splash stainless steel strainer. The outlet valve of weigh bowl is suited for manual or air actuated operation. The operator makes direct reading of the weight of the milk on the scale and records it separately for individual suppliers. Automatic printing of weight is also possible. The milk in tanker (road/rail) may be measured in volume by passing it through a flow-meter or in weight by using a weigh bridge where tare weight of the tanker is deducted from gross weight of it.
vi. Sampling of Milk
Samples may be drawn during reception of milk for chemical and microbiological analysis in the laboratory. Only representative sample, without any type of adulteration, dilution and contamination should be drawn using correct technique and appropriate device. While strict precautions regarding sterility of the stirrer,sampler, container, etc. are required for obtaining a microbiological sample and dryness and cleanliness of the above appliances should suffice for a chemical sample. Test cannot be accurate unless the test sample is truly representative of the product to be tested. Samples from milk containers may be drawn with the help of a suitable device. The characteristics of various devices have been listed in Table.
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| Characteristics of Milk Sampling Devices |
Sampling methods: Sample should be taken after thorough mixing of milk with the help of plunger or sampler (devices) or some other means.
i) From a small handy batch: Milk is properly mixed before taking sample.
ii) From a large batch: Milk in can or vat or small tank can be mixed by using a plunger manually. Minimum ten times from top to bottom plungering will ensure adequate mixing before drawing sample. Mechanical stirring can also be done wherever facilities available. Vigorous stirring is avoided as milk may get churned at temperatures between 26.5 and 29.5 0C.
iii) From several containers of different size, shape and type: If a large vat is available, milk of all the containers are mixed in vat and a sample is drawn.
iv) From bulk units: Nos. of cans filled from storage tank/bulk unit is not required to be sampled individually. The number of random cans to be sampled shall be as follows:
v) From storage tanks/rail/road tankers: Method of sampling is governed by storage/transport conditions. So, no rigid procedure of sampling can be prescribed.However, a recommended procedure described below may be followed.
Milk is thoroughly mixed by using either a sufficiently large plunger or a mechanical agitator or compressed air till a complete agreement is obtained between samples taken at the manhole and the outlet cock with respect to Fat and SNF. Plunger is inserted through manhole and, pushed forward and pulled back, downward and back, and backward and back in cyclic order repeatedly for not less than 15 minutes. Sampling is done through the stopcock in the tank door or from a valve in the discharge line from the tank as it is being emptied.
Milk is thoroughly mixed by using either a sufficiently large plunger or a mechanical agitator or compressed air till a complete agreement is obtained between samples taken at the manhole and the outlet cock with respect to Fat and SNF. Plunger is inserted through manhole and, pushed forward and pulled back, downward and back, and backward and back in cyclic order repeatedly for not less than 15 minutes. Sampling is done through the stopcock in the tank door or from a valve in the discharge line from the tank as it is being emptied.
vii. Dumping of Milk
After weighing and recording, the milk can be discharged into the dump tank situated below through stainless steel chute between the weigh bowl and dump tank. Dump tank should be of sufficient capacity to avoid delay or overflow of milk,at least one and half times but not more than 3 times the capacity of the weigh bowl. An electronic milk level control may be installed in the dump tank to eliminate the possibility of loss of milk from overflow.
Layout of Reception Dock and Equipment
i. Important Considerations
Layout at the reception dock and equipment placement is done for obtaining the maximum efficiency at the minimum cost.
Health regulations: Local health authorities requirements must be met. It is absolutely necessary to consult the health authorities while the drawings are in preliminary form and to get formal written approval before construction is started.
Volume of milk: The reception platform should be large to accommodate necessary number of milk can lorries and road/rail tankers to be unloaded at a time. The seasonal variation in milk availability should also be taken into account.
Methods of delivery of milk: Whether milk is being delivered by individual producers, route hauler, tank truck, tank car, tanker or any combination of these,layout of platform and equipment should take care of. A good layout of conveyors at the reception dock contributes much to efficiency. To unload trucks without delay, the trucker should be able to discharge all of his cans at the intake point before moving to the next position to pick up his empties. To avoid the need of a man to take empties from the discharge conveyor, the combined capacity of the intake conveyor, the washer, and the discharge conveyor should be sufficient to hold all the cans from the largest route.
Floor space: Adequate space and equipment must be provided for proper inspection of milk and for handling cans containing rejected milk until they can be tagged and reloaded on the hauler’s truck for return to the producers. Location of equipment either too close to each other or nearer to walls or ceiling should be avoided.Sufficient space be provided for conveying incoming and outgoing cans, weighing,sampling and dumping of milk. Emptied cans and lids should be properly washed and returned to the trucker Location of driveways and vehicle yards: Streets, driveways and yards for the vehicles must be located suitably in relation to the receiving dock.
Elevation of dock: The level of the truck and receiving platform should be the same.
ii. Equipment and Devices at Reception Dock
The layout of equipment must provide the most economical use of available floor space. The equipment are so arranged as to obtain the maximum processing volume per man-hour. Provision for future revisions or expansion, which will involve a minimum change and expense, must also be made. These plans must comply with the building and health regulations of the particular area. The possible equipment and devices required on a dairy reception dock have been listed in Table.
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| Equipment & Devices at Milk Reception Dock of a Dairy Plant |
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| Equipment & Devices at Milk Reception Dock of a Dairy Plant |
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| Equipment & Devices at Milk Reception Dock of a Dairy Plant |
Milk Reception at the Dairy Dock
Milk may be delivered to the dairy plant either in cans or in tankers (road/rail). The place in the dairy plant, where milk first arrives and is received after grading for acceptance, is known as milk reception dock or platform or raw milk receiving dock (RMRD). Dairy reception dock is especially designed and equipped to facilitate rapid reception of milk and, cleaning and sterilization of used containers.
Since further processing of milk mainly depends upon its quality, the decision of accepting the milk, must be done quickly immediately after arrival and, thorough investigation. Milk reception should be so planned and the equipment so chosen that intake operations are expedited, particularly where large volumes of milk are received. Delay may lead to deterioration of milk awaiting dumping and, increase in labour and operating costs of the can washer. So, the deliveries of milk should follow a schedule and reception be completed within stipulated period of 2 to 3 hours to facilitate the following plant operation un-interrupted, especially in tropical countries.
Since further processing of milk mainly depends upon its quality, the decision of accepting the milk, must be done quickly immediately after arrival and, thorough investigation. Milk reception should be so planned and the equipment so chosen that intake operations are expedited, particularly where large volumes of milk are received. Delay may lead to deterioration of milk awaiting dumping and, increase in labour and operating costs of the can washer. So, the deliveries of milk should follow a schedule and reception be completed within stipulated period of 2 to 3 hours to facilitate the following plant operation un-interrupted, especially in tropical countries.
Key Words
Adulteration: Adding to or subtracting from food.
Bulk tanker : Insulated, cylindrical tank mounted in a horizontal position on trailer wheels or on the truck to be used to pick up of bulk milk.
Collection centre : A place where milk produced in rural area is collected for processing or marketing.
Milk shed : A defined area having sufficient milk surplus.
Planning : A scheme of action
Refrigeration : A Machine used for cooling the milk.
Route : A road for passage/travel
Survey : To take a view for specific study.
Transportation : Act of carrying/conveying from one place to another.
Bulk tanker : Insulated, cylindrical tank mounted in a horizontal position on trailer wheels or on the truck to be used to pick up of bulk milk.
Collection centre : A place where milk produced in rural area is collected for processing or marketing.
Milk shed : A defined area having sufficient milk surplus.
Planning : A scheme of action
Refrigeration : A Machine used for cooling the milk.
Route : A road for passage/travel
Survey : To take a view for specific study.
Transportation : Act of carrying/conveying from one place to another.
Let Us Sum Up
Establishing a milk collection system is based on the considerations of basic characteristics of milk, size of production units, density of milk production, distance and type of market. These lead to a variety of systems, incorporating different measuring and testing arrangements. The aim is an efficient and fair system of collection. Having clear vision, organization of a milk collection system is done by following certain steps-ensuring milk potential, location of milk-shed and collection centres, establishing the collection centres, ascertaining management controls, setting out operating procedures and deciding on the supervision and control of the centre.Participation of producers as a representative in collection of milk is also ascertained to solve their problems.
Type of milk collection system includes supply of milk to the processing plant directly, through collection and/or chilling centres and through multi-stages of handling.Varieties of containers, made of different materials and of various shape, size,capacity and designs are used at different points of milk handling and processing.
Method and modes of transportation have been summarized in Table
Type of milk collection system includes supply of milk to the processing plant directly, through collection and/or chilling centres and through multi-stages of handling.Varieties of containers, made of different materials and of various shape, size,capacity and designs are used at different points of milk handling and processing.
Method and modes of transportation have been summarized in Table
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| Methods and Modes of Transportation of raw milk |
Transportation of Raw Milk
The dairy plants organize the collection and transportation of milk in its collection area. Route plans need to be established and continuously optimized for an optimal utilization of the transport facilities and keeping transport cost low. Some sorts of transportation are also required to carry the milk from points of production to the points of collection, pick up, chilling or processing.
i. Purpose
Milk being perishable commodity, it becomes necessary to transport the fresh raw milk to the consumer or the chilling/processing plant within 4 hours of its production.Thus, transportation becomes an integral part of milk collection system. An efficient and suitable facility is selected on the basis of the raw milk collection as well as regional requirements.
ii. Factors determining selection
The following factors may be considered in selection of a suitable, efficient and economic transportation system and transport:
Geographical location: In hilly areas where roads are not developed, small quantity of milk can be carried out on head for short distance and on shoulder sling for comparatively longer distance and larger quantity. In places where river is to becrossed, a boat and road in combination may be used.
Volume of milk: For small quantity and short distance head load, shoulder sling,cycle, etc; for moderate quantities and longer distance motor cycle, cart, tri-wheeler,etc. by road can be transported. If quantity of milk is large, milk in cans on truck & lorries or in road/rail tankers for long distances can be carried.
Variable resources: If the organization is having road/rail tankers and facilities exist for bulking, chilling, loading and unloading, road/rail tankers may be used. In absence of such facilities, only milk in cans or tanks on truck or lorries is transported.Cost of transportation: Cost of transportation should be kept at minimum level by selecting a suitable transport of optimum size and capacity taking into consideration the quantity of milk to be transported, type of vehicles available, road condition and time involved.
Distance of transport: Depending upon the distance of transport and quantity of milk, a most economic type of transport system is selected.Condition of road: Condition of road such as dusty, narrow, broken, having sharp turnings, congestion, business, obstacles like railway crossing, etc. are also taken into account in selecting a suitable vehicle for milk transportation.
Own vs. hired: Having own transportation system is too expensive and highly cumbersome. Apart from the initial investment on vehicles, it involves a complete section of maintenance and operational personnel. Even after involving a considerable time, energy and money, the system is neither cost effective nor working satisfactory.On the other hand, hired transport facilities are very effective and relieve the management from several problems and evils. It is economical because of no or low investment and maintenance expenses. The dairy has an agreement with the owner of the vehicle regarding rate, mode and interval of payment, liabilities on account of delays, spoilage of milk, accidents, pilferage during transit, change in the quality due to any fault on his part, etc. Heavy penalties and recoveries are imposed for any lapse on the part of the transporter.
iii. Methods
Generally following methods are being used in dairy industry:
Head load: Generally, producers carry milk on their head to nearby collection/chilling/processing point. This is being practiced in villages to carry small quantity(3 to 25 litres) of milk for short distances (3-8 km) to the collection point, specially in hilly areas where there is no development of road.
Shoulder sling:Use is restricted to hilly areas or other areas where no other means of transport is easily available. When the milk is slightly more (20 to 40 liters) and conveniently can not be carried on head, for little more distance (5 to 10 Km), this method is practiced.
Bullock cart: In villages where no road exists in real sense, bullock cart is used to carry milk, if quantity is more (300–400 Kgs) and distance is to be covered within 1 to 2 hours. It is very slow moving vehicle.
Tonga (Horse cart) : It is faster than bullock cart but it needs road to ply on and carries comparatively less load (200-250 Kgs) for more distances (10-15 Kms).Pack animal: Ponies, horses, donkeys and bullocks are usually employed to carry 40 to 80 Kgs to a distance of 5 to 10 Km. This method of transport is faster than bullock cart but slower than tonga.
Bicycles: Bicycles are commonly and conveniently used to carry milk to the collection centres, pick-up points and chilling/processing points. It is also used to carry milk in unorganized sector by middlemen/agents/vendors to sell milk in the accessible urban area. It is faster, more convenient and easily accessible to milk producers/consumers home. About 40 litres (l) of milk for a distance of about 10-
15 Km can easily be transported.
Motor Cycle: Still heavier duty then bicycle can be taken to cover more than 15 Km and carry more than 100Kg of milk in very short time.
Tricycle or cycle rickshaw: It can carry more load than cycle.
Auto rickshaw: It can carry more load than cycle, rickshaw/motor cycle.
Boat: Boat is used to cross-river. Normally, small boats carry about 200 l of milk for short distances.
Motor trucks: Motor trucks carry milk in cans and bulk tanks to a load of 0.5 to 3.5 tons for more than 100 Km. With the improvement in road facilities and construction of all season roads, motor trucks have been found most effective
means of transportation.
Railway wagon: Railway wagons are most dependable and economical for long distance but less popular means of milk transportation. Railway wagon can carry 10 to 12 tons of load for more than 100 Km.
Road tanker: Insulated stainless steel tanks are mounted on road truck chesis for bulk handling (3000 – 12000 l) and for long distance (100 to 1000 Km.) transportation.The tanker may be divided into 2 to 3 equal capacity compartments with separate outlets.
Rail tanker: Insulated and/or refrigerated stainless steel tanks are mounted on rail truck/chesis of the capacity in the range of 10,000 to 50,000 l to transport milk for a long distance 500 to 3000 Km or more.
The extent, structure, distance of the collection area and form of collection, determine the selection of mode of transportation.
Tonga (Horse cart) : It is faster than bullock cart but it needs road to ply on and carries comparatively less load (200-250 Kgs) for more distances (10-15 Kms).Pack animal: Ponies, horses, donkeys and bullocks are usually employed to carry 40 to 80 Kgs to a distance of 5 to 10 Km. This method of transport is faster than bullock cart but slower than tonga.
Bicycles: Bicycles are commonly and conveniently used to carry milk to the collection centres, pick-up points and chilling/processing points. It is also used to carry milk in unorganized sector by middlemen/agents/vendors to sell milk in the accessible urban area. It is faster, more convenient and easily accessible to milk producers/consumers home. About 40 litres (l) of milk for a distance of about 10-
15 Km can easily be transported.
Motor Cycle: Still heavier duty then bicycle can be taken to cover more than 15 Km and carry more than 100Kg of milk in very short time.
Tricycle or cycle rickshaw: It can carry more load than cycle.
Auto rickshaw: It can carry more load than cycle, rickshaw/motor cycle.
Boat: Boat is used to cross-river. Normally, small boats carry about 200 l of milk for short distances.
Motor trucks: Motor trucks carry milk in cans and bulk tanks to a load of 0.5 to 3.5 tons for more than 100 Km. With the improvement in road facilities and construction of all season roads, motor trucks have been found most effective
means of transportation.
Railway wagon: Railway wagons are most dependable and economical for long distance but less popular means of milk transportation. Railway wagon can carry 10 to 12 tons of load for more than 100 Km.
Road tanker: Insulated stainless steel tanks are mounted on road truck chesis for bulk handling (3000 – 12000 l) and for long distance (100 to 1000 Km.) transportation.The tanker may be divided into 2 to 3 equal capacity compartments with separate outlets.
Rail tanker: Insulated and/or refrigerated stainless steel tanks are mounted on rail truck/chesis of the capacity in the range of 10,000 to 50,000 l to transport milk for a long distance 500 to 3000 Km or more.
The extent, structure, distance of the collection area and form of collection, determine the selection of mode of transportation.
iv. Transport vessels
- Milk cans: 40-50 litre milk cans up to 3000 litres per truck.
- Farm containers: Made of stainless steel, mobile and insulated (partially with chilling) of 200 to 500 litre capacity.Tanks installed on trucks: Insulated and/or refrigerated of capacity 600 to 3000 litre tanks mounted on truck to receive milk on the route.
- Milk tankers: Separated into several chambers with or without an integrated reception device and data recording of capacity 3,000 to 50,000 litres milk.
- Transport pipes: Subterranean pipelines made of stainless steel in developed countries for transporting milk between the dairy and collecting point. Milk is pushed or flowing by gravity at suitable location.
Type of Transport:
Roadways, railways, waterways and air ways are the possible types of transport. Sometimes combination of two or more can also be used for transporting milk. In selecting suitability of a type of transport, volume of milk,geographical location of the area, availability of facilities and ultimately the cost of transportation are taken into account. A comparative advantages of can vs. tankers and road vs. rail transport have been given in below Tables respectively.
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| Comparative advantages of can and tanker transport |
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| Advantages of road and rail transport |
Containers for Milk collection
Various types of containers made of different materials, sizes, shapes and designs are used in milk handling at pick up-points, collecting centres, collecting and cooling centres and finally for delivering to the processing plant.
i. Materials of Construction/Fabrication
Wood, plastics, porcelain, glass, metals etc. are used for fabricating different type of milk containers of several uses (Table).
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| Type of containers and their uses |
ii. Design of Milk Containers
Milk containers must be designed in such a way that all the parts of a container are accessible for cleaning, sanitization and inspection. The container must give protection to milk from spoilage, light penetration and contamination. Some small-scale farmers use cans which were previously used as packaging material for other foods. Such cans may have joints which are not accessible to washing operations.
iii. Containers on the Farm
Type, size and design of containers depend on the farm operations and size of the herd. Milking is usually done by hand in small organized farms. Machine milking is limited to the large-scale government/institutional farms. For hand milking, wide mouthed buckets made of aluminium or stainless steel are used. In some farms,small-mouthed milking pails are prevalent.
At the end of the milking process, the herd’s milk is pooled into one or a few containers. For this, milk cans, bulk tank,refrigerated or insulated vats/tanks with lid to cover, and similar type of containers may be used. The following is the list of equiment and containers used at organized farms:
- Milking machine
- Milking pail
- Weight balance, platform type
- Storage milk cans
- Storage vat
- Bulk storage tank
- Can cooling system
- Milk sampling and testing unit
- Bulk tank cooler
iv. Individual Farmers’ Containers
Farmers in rural area have very small holding of milch animals, usually in the range of 1 to 3 in number. They use the containers varying in size and of materials for milking, storing and carrying to collection point for delivering the milk. Types of containers in use at farmers’ house are:
- Buckets made of galvanized iron, brass, aluminium, stainless steel, etc.
- Milking pail of galvanized iron.
- Baked earthen pots.
- Pitcher of brass, earth or copper.
- Tumbler, jug etc. of brass, bronze, aluminium, mild steel and stainless steel.
- Second hand package container of tin, plastic etc.
- Measures of bronze, aluminium or chrome plated iron.
It is advisable for individual farmers to acquire containers fabricated from approved materials and of standard size. Standard size milk cans ranging from a few litres to the large 40 to 50 litres are available in the market. Farmer organizations should assist the small-scale farmers to acquire milk containers of the right size and design for proper protection in terms of keeping quality, chemical composition, microbial quality, taste and flavour, and also for making handling easier.
Standard containers allow the use of mechanical devices in conveying, tipping,washing, sterilizing, interchanging of lids, loading and unloading. It is easy to control the price of standard equipment throughout the market-both nationally and internationally.
v. Containers at Pick up Points
i. Materials of Construction/Fabrication
Wood, plastics, porcelain, glass, metals etc. are used for fabricating different type of milk containers of several uses (Table ).
ii. Design of Milk Containers
Milk containers must be designed in such a way that all the parts of a container are accessible for cleaning, sanitization and inspection. The container must give protection to milk from spoilage, light penetration and contamination. Some small-scale farmers use cans which were previously used as packaging material for other foods. Such cans may have joints which are not accessible to washing operations.
iii. Containers on the Farm
Type, size and design of containers depend on the farm operations and size of the herd. Milking is usually done by hand in small organized farms. Machine milking is limited to the large-scale government/institutional farms. For hand milking, wide mouthed buckets made of aluminium or stainless steel are used. In some farms,small-mouthed milking pails are prevalent.
At the end of the milking process, the herd’s milk is pooled into one or a few containers. For this, milk cans, bulk tank,refrigerated or insulated vats/tanks with lid to cover, and similar type of containers may be used. The following is the list of equiment and containers used at organized farms:
- Milking machine
- Milking pail
- Weight balance, platform type
- Storage milk cans
- Storage vat
- Bulk storage tank
- Can cooling system
- Milk sampling and testing unit
- Bulk tank cooler
iv. Individual Farmers’ Containers
Farmers in rural area have very small holding of milch animals, usually in the range of 1 to 3 in number. They use the containers varying in size and of materials for milking, storing and carrying to collection point for delivering the milk. Types of containers in use at farmers’ house are:
- Buckets made of galvanized iron, brass, aluminium, stainless steel, etc.
- Milking pail of galvanized iron.
- Baked earthen pots.
- Pitcher of brass, earth or copper.
- Tumbler, jug etc. of brass, bronze, aluminium, mild steel and stainless steel.
- Second hand package container of tin, plastic etc.
- Measures of bronze, aluminium or chrome plated iron.
It is advisable for individual farmers to acquire containers fabricated from approved materials and of standard size. Standard size milk cans ranging from a few litres to the large 40 to 50 litres are available in the market. Farmer organizations should assist the small-scale farmers to acquire milk containers of the right size and design for proper protection in terms of keeping quality, chemical composition, microbial quality, taste and flavour, and also for making handling easier.
Standard containers allow the use of mechanical devices in conveying, tipping,washing, sterilizing, interchanging of lids, loading and unloading. It is easy to control the price of standard equipment throughout the market-both nationally and internationally.
v. Containers at Pick up Points
The individual farmer’s containers are handled at pick up points. At the point,sometimes milk from many farmers is pooled into fewer and larger containers. Use of standard containers reduces the time of weighment of milk of the individual farmers/suppliers.
vi. Containers for Collecting and Cooling Centers
Milk from small-scale farmers is collected daily once or twice, and delivered to a processing plant. Evening milk is collected, cooled and held cold overnight for delivery to the processor together with the following day’s morning milk. The final delivery of milk to the processor is done mainly in 40-50 litre aluminium alloy cans(may be insulated also) or in bulk tanks.
vii. Containers for Bulk Milk
Bulk milk collection is carried out either in 40-50 litres cans loaded on lorries or pick up or it may be collected using bulk pick up road tankers where the infrastructure allows. Single wall cans are usually used. In few cases, insulated cans are used.After delivery, the processor washes and sanitizes the cans and returns to the collection and/or cooling centre.
Road bulk pick up tankers are used to transport milk from collection or collection-cum-cooling centres. A tank may be equipped with a pump and hose, weighing facilities or a flow meter, sample bottle with an in-built automatic sampling line.Bulk pick up tankers are usually constructed with an insulation layer of cork,polystyrene or mineral wool. The tanker may be refrigerated or simply insulated.
The individual farmer’s containers are handled at pick up points. At the point,sometimes milk from many farmers is pooled into fewer and larger containers. Use of standard containers reduces the time of weighment of milk of the individual farmers/suppliers.
vi. Containers for Collecting and Cooling Centers
Milk from small-scale farmers is collected daily once or twice, and delivered to a processing plant. Evening milk is collected, cooled and held cold overnight for delivery to the processor together with the following day’s morning milk. The final delivery of milk to the processor is done mainly in 40-50 litre aluminium alloy cans(may be insulated also) or in bulk tanks.
vii. Containers for Bulk Milk
Bulk milk collection is carried out either in 40-50 litres cans loaded on lorries or pick up or it may be collected using bulk pick up road tankers where the infrastructure allows. Single wall cans are usually used. In few cases, insulated cans are used.After delivery, the processor washes and sanitizes the cans and returns to the collection and/or cooling centre.
Road bulk pick up tankers are used to transport milk from collection or collection-cum-cooling centres. A tank may be equipped with a pump and hose, weighing facilities or a flow meter, sample bottle with an in-built automatic sampling line.Bulk pick up tankers are usually constructed with an insulation layer of cork,polystyrene or mineral wool. The tanker may be refrigerated or simply insulated.
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