Dairy Building Sanitation

A clean and well maintained dairy building and its surrounding promotes cleanliness habit amongst labour force and quality of its products. It automatically gives positive publicity and awareness to public for quality of products. A clean surrounding gives a sense of pride. A regular inspection by a team of decision makers helps in identifying the areas that need attention. It includes plant surrounding (Land Scape),condition of building, equipment and machinery, storage and warehousing, lighting,services/drains, hygiene of employees, toilets, dressing rooms, canteen, drinking water zone, insects/rodent infestation etc.

There are some indicators for clean and efficient dairy plant. These will reflect how good a plant is:

• Toilets and workers amenity rooms are the first in the list. A neat and clean, well ventilated, odourless toilets indicate the level of sanitary practices in the plant. Workers dressing room be well lighted, and should have enough space.
• Floors should be clean, shiny and throwing of trash behind doors or under the benches should be discouraged.
•  Building premises should not harbour broken or discarded equipment/furniture.
• Trash and rubbish should not be thrown around that creates breeding ground for insects and rodents.
•  Wall, floor and ceiling should remain clean, dry and well painted. In the dairy,light colour paints are used for walls and ceiling to reflect dirt or deposit for immediate attention. There should be proper lighting and water or dirt should not be accumulated at any point on the floor. Insects and flies should be adequately prevented entering in the milk-processing zone. Doors and window should have
• wire mesh covers and even air curtains should be provided. These air curtains produce thin layer of high-speed air to prevent entry of flies.
•  Mould control is also important since the dairy plant uses lot of water, hence,more humidity causing moist environment. This is conducive to mould growth. To prevent this, all exposed surfaces should be kept dry. These are brushed, cleaned with soft detergent and a spray of 5000 ppm of sodium hypochloride is done. This destroys the mould spores. Further spray of quarternary ammonium compound is done to inhibit mould growth. This should be repeated every week.
•  Insect and rodent control in general should be practiced. There should be no accumulation of dirt/ filth inside as well as outside. The garbage and wastes act as breeding place of insects. Good insecticide spray can be performed around the drains of dairy plant. For outdoor spray, Methoxychlor, Malathion or permitted insecticide with recommended strength could be used. All equipment is covered to avoid entry of these insects and pest. Rat proof building designs are made. Building openings are plugged. Height of the floor and steps are made such that rats cannot jump or climb. If at all, the rats find entry, they should be eliminated

Maintenance of Rubber and Gaskets

Dairy equipment have number of joints and connections requiring leak proof arrangement. Stationary equipment like plate type heat exchanger (chiller or pasteurizer) will have gaskets between individual plates. Moving or revolving equipment such as pump shaft or cream separator will require shaft seals, ‘O’ rings etc.

i. Characteristics of rubber and gaskets

All of these must be chemical resistant, as acid and alkali are used as detergents.These should be resilient to offer leak proof joints. These are of varied shapes and sizes to suit particular location or purpose for which these are used. They are required to work under high temperature and preserves, yet should not got damaged or contaminate the milk and milk products. It is, therefore, important that the rubber and gaskets should be of non-toxic material, should be heat resistant, durable and should not get damaged with the chemicals used for cleaning.

ii. Care with gaskets and seals

These have comparatively shorter life, hence require utmost care. Since these are between joints or moving parts, over tightening be avoided. You will notice leakage from pasteurizer at the start. Slowly the leakage will reduce and may stop without tightening the plates. This is due to heat expansion taking place. If you notice leakage even after enough warming up, then plates may be tightened. Over tightening may permanently deform the gaskets. This will result in reduced thickness/gap between the plates. Ultimately, this will affect the capacity of pasteurizer. Similarly packing/’O’ ring in the union or joint should not be over tightened. Usually a good joint should be leak proof. This could be made leak proof by hand tightening and does not require a spanner. Gaskets between pipe joints get damaged while reassembling. This is due to poor alignment of pipelines. As discussed in the previous chapter, the alignment must be corrected before tightening the joint.

iii. Pump seals

These also need good care. Seals are expensive and require correct assembling.The carbon seal face rubs the stationary wall of the pump body, hence, the surface should be well polished and clean. While fixing the new gasket, old gasket and its particles should be removed with either a gasket remover or cleaned with the help of a sand paper.

Care of Pipes and Fittings

You will find that a milk processing plant is full of various types of pipes. Various utilities like milk, water, air, steam, chilled water, hot water, refrigerant, electricity,etc. are transported/conveyed through these pipes. To regulate and control flow,different valves and fittings are provided within this piping network. This network must work without the loss of product, energy, corrosion, noise/vibration, leakage, etc. They should also offer ease in working and accident free operation.

i. Care of pipelines

Pipeline once laid, very little can be done. Only protection from moisture, oxygen and acidic environment should be done. If pipe is imbedded in soil, asphalt covering will protect it. Overhead pipes are kept dry and painted. Inside pipe corrosion can only be minimized if entry of oxygen could be reduced. Even dissolved oxygen in water affects it.

ii. Care during installation of pipes
Water hammering is due to movement of water with jerk. This is caused by sudden closure of opening of fluid and accumulation of residual fluid inside pipe. This obstructs the normal flow. Hence, pipelines are given proper slope and drainage point to avoid any accumulation. Pipe supports are adjusted to give proper slope to the pipes.

iii. Maintenance of pipes joints
Some pipes carry hot and cold fluid like steam and chilled water. The temperature change causes thermal expansion of metallic pipes. These pipes have provision to absorb expansion. Check for roller support and expansion joint/loops of pipes.Similarly, the leakages from pipe joint should never be allowed to continue. As soon as a leak is noticed, it should be plugged by replacing the gasket or correcting the alignment.

iv. Care with pipe insulation

You will note that certain pipes have insulation covered with Aluminum cover (cladding). Pipelines carry hot or cold fluid. Steam line is insulated with glass wool reinforced with chicken wire mesh and cladded for long life. Similarly, chilled and refrigerant lines are covered with thermocole insulation and cladded. We must ensure proper insulation if it is found removed or not in good condition.

v. Care of valves and fittings
These are integral part of pipeline system and of different types and shapes. Valves may develop leakage either from gland of the stem or valve seat may not close the valve fully. If gland is leaky, it is repacked and lightened. The stem threads of the valve should also be lubricated if the gland is dry. The valve seat is also cleaned and grounded if seating is not proper. In most of the cases valves are replaced.Fittings, i.e., the elbow, bends, unions, flanges, sockets, tee, cross, plug, etc. help in change of direction or connection to the equipments. Usually for any defect,these are replaced.

Care and Cleaning of SS Surface

Stainless steel (SS) is expensive metal and therefore, needs care. The frequency and the extent of cleaning depend on the extent of usage and the condition.

i. Cleaning of soft deposits

Ordinary deposits like dirt, grease are cleaned with mild detergent (soap) and washed and dried.

ii. Hard deposit

However, hard deposits need different treatments such as rubbing/buffing withpolishing powder and SS brushes. Soft cloth or pads are used to shine the surface.Plastic sponge or fibrous brushes are also safe to use. Avoid iron wire brush (steel brush) and should never be used for rubbing. This brush will leave iron particles on S.S.surface, which will cause rust.

iii. Care with sanitizers
If Chlorides/Bromides/Iodides based chemicals used under acidic condition for long;there are greater chances of corrosion, hence should be washed properly.

iv. Care with salt solutions

These leave dirty spots on drying, hence should be washed after use. No paint or any coating is done on SS surface. Sometimes rust like appearance may occur which is due to some iron chip or part adhered on SS surface for cleaning. 5 to 15% caustic soda (hot or cold) is commonly used. Sometime 0.1 to 2.0% hot solutions of Sodium Metasilicate, tri-Sodium Hexa Metaphosphate, and Tetrasodium pyrophosphate, Sodium Tripolyphosphate are used as excellent removers.Organic solvents are sometimes used to remove oil, grease, paints or hard deposits.These organic solvents are ether, alcohol, kerosene, gasoline, etc. Highly adherent ink, paint, etc. can be removed by butyl acetate. For very heavy water deposits,15-20% nitric acid can be used with caution. Acid cleaning is followed by proper washing to remove any trace of acid.

Guidelines for Effective Lubrication

A guideline for proper lubrication of the equipment for any dairy plant can be prepared from the recommendations made in manuals of individual equipment.Manufacture of equipment does indicate the type, quantity and lubricant required.From various lubricants recommended, a common list of lubricants could be prepared to minimize diversified needs. Mark the points of lubrication on equipment and in the record book. Then, plan a schedule and route for technician. Evaluate the suitability of lubricant application method and change if required. Normally the cost of lubricants ranges from three to ten per cent of the machine cost.With the information gathered, a “Route Map” could be prepared. This map covers all machines that can be lubricated in one shift or a day. This way daily, weekly,monthly, quarterly, semi-annual and annual lubrication chart are prepared. A Supervisor or Engineer needs to monitor these charts for effective lubrication programme.

Development of Plant Maintenance Programme

The very first step for development a PM programme is to record basic equipment data with appropriate classification. Recording should be simple but reliable. Usually card file system known to engineers could be adopted. This information can be required any time, hence, be readily available and preserved.

i. Administrative information
This should include equipment’s name, its supplier, sanction order, date of purchase,date of commissioning, its cost, etc. This will be needed at later date.

ii. Technical details
Information such as serial No./model/style, capacity/speed/rating or size,recommendations of manufacturers for installation/operation/lubrication type and quantity/frequency of lubrication replacement and precautions, if any.

iii. Specific details

Mechanical, electrical and utilities required such as regular water, soft water,refrigerant, steam, fuel, electricity, compressed air, and quantity of effluent discharge,etc. It may also record the working pressure and temperatures, voltage, insulation and the inventory number given while entering in record to identify it.

iv. Identification of critical points

Now decide the list of specific points of each equipment to be inspected, and point/area, which should not be inspected. Obviously the point, which wears out fast or gets eroded/damages, needs regular inspection. The parts dangerous to the worker or likely to stop the plant operation should be avoided. Natural question comes in mind is as to what to inspect. The answer will be from the recommendations of equipment manufacturers manual. Then prepare a checklist in the order of priority.The idea is to give a written guideline to the person who will carry out inspection.This checklist helps to recall and assure proper execution instead of leaving on the memory of the individual.

v. Frequency of check-up/inspection
It is decided based on the condition of equipment. Older equipment needs frequent inspection as compared to newer ones. Similarly, there may be safety recommendations; hence, frequency of inspection will be increased. The extent of equipment used and the type of wear will also play role in deciding the frequency.

vi. Equipment performance

Finally, we should keep on evaluating the performance of equipment. Normally equipment performance will decrease with time. It will then increase cost of production. The report/remark of operator in the logbook will act as a feedback.Hence these comments be seen and compared with the manufacturer’s recommendations. If it is felt that the performance in term of flow, capacity, quality,utility consumption etc. are above normal then actions are required.Planning is then made as to when to shut down the equipment, what spare parts are needed and made available. It is also assessed as to whether skill is available within the maintenance group or help from outside will be needed. How much financial burden will be on the dairy and if the money is available. These are some of the crucial pints of judgment of efficient PM programme.

Principles of Preventive Maintenance

Dairy equipment are expensive due to their specialized construction. Some of these are sophisticated and imported, hence, needs proper attention. In general, there is less appreciation to the maintenance activity, Preventive Maintenance (PM). Its importance is realized at the time of break down. A PM programme is a “procedure” designed to increase plant productivity, decrease maintenance, reduce operating cost, and to increase life of the equipment. It involves:

i. Routine external inspection

It means external viewing in terms of noise, vibration, heating or any sign of malfunctioning. This is noted and corrected, if any.

ii. Periodic internal check-up

It is done when the equipment is shut down at the end of operation. This is not a major repair action. One has to decide the duration after which this check up is done. In this adjustment of control instruments, replacement of lubricants, surface touch ups, etc. are carried out. During this check up, looking at the condition of equipment can make an idea on the possible major over-haul.

iii. Major repair/over-haul
Major repair is then planned preferably in the season when the equipment is not in use. Most of the major repairs are carried out during summer month when the milk handling capacity is less. For refrigeration section, the repairs are planned in winter months. Prior to shut down selection, procurement and stocking of spares must be ensured.

iv. Evaluation of equipment performance

A good engineering function is to carry out routine evaluation of each and every equipment. Due to normal operation, the efficiency of equipment reduces; this in turn affects the productivity. There are set procedures to calibrate and measure the flow capacities, heat transfer efficiency, product output, utilities consumption, etc.Again the frequency of such evaluation is a matter of experience and planning. The awareness on the part of management is also an important factor.

v. Record keeping is a part of PM procedure

We must maintain the work and breakdown record of the individual equipment.This will also indicate the repairs carried out. These records help in subsequent planning. These records are called “Log books”. Proper proforma is developed to indicate exact duration of running, various inputs utilized, efficiency and check parameters, records of repair and nature of complaint and the person who carried out the operation and repair. Periodic verification is carried out by superiors as a check and feedback.If above procedures are adopted, the cost of maintenance will be less, equipment efficiency will improve, plant productivity will increase, accident possibilities are avoided, and finally the life of expensive equipment is extended.

Preventive Maintenance of Dairy Plants and Machineries

We have learned various equipment required for the manufacture of milk products. An attempt was made to enrich with the operation of different equipment involved in the processing of most common milk products. Yet some special milk products could not be covered. However, the exposure given will give enough background knowledge to understand other equipment.

We will learn as to how to prolong life of equipment with proper planning. As we know the milk processing equipment are expensive, hence, need greater care to give best results. One way to maintain the equipment is to run as long as it works and repair it when it stops working. It is called “Breakdown Maintenance”. A scientific way of maintenance would be to do “Preventive Maintenance”(PM). As a thumb rule 6-12% of machine cost will be required for proper maintenance of machine every year.

In order to carry out PM programme, planning is done. We will learn different records and forms used to follow up schedules. These will act as guidelines for plant operators. These records also indicate the preparations for future planning. What are the needs of spares, oils and greases, etc., can be easily decided. Oilingand greasing is lifeline for individual machine. Every equipment has been recommended a lubrication schedule. For every dairy plant, daily, weekly, monthly and quarterly planning can be done. A lubrication route for the technician can be suggested and appropriate checks planned.

Dairy equipment are required to work under unfavorable conditions of high moisture,chemical environment, and temperature and pressure stresses. These conditions do affect the life of material with which the equipment is fabricated. Also the aesthetic look of equipment is need of such industry. It gives psychological impression to workers and the public for the conditions prevailing within the plant.

All the processing equipment need water, steam, refrigeration, air and electricity.These are supplied through appropriate pipelines and cables. Well-maintained service lines not only reduce the losses but also offer good look. Injuries and accidents can also be prevented with little care.Most of equipment are provided with components made of rubbers. These are unavoidable, yet designed with utmost care. To maintain quality of product the upkeep of these components are a must. Readers will learn, as to how to take care
of these parts and prolong their life.

Finally, even if each and every equipment is in order, the plant surrounding, landscape sanitation needs utmost care. Building maintenance is the first impression given to the visitors and public who pass by this unit. All walls, seepage, odour, well-trimmed grass and shrubs, well parked vehicles, etc. offer reputation of the dairy plant, as a first impression. A summary of civil maintenance will be discussed.

Paneer, Chhana & Casein Making Equipment

These products are acidic coagulated milk products unlike cheese discussed earlier.Paneer is prepared by coagulating standardized heated milk. Curdled mass is pressed to get paneer and the whey is allowed to be drained-off, while Chhana is unpressed mass usually prepared from cow’s milk. Following equipment are used:

i. Vat

The heating and coagulation of milk is done in a stainless steel double walled vat. A The stirring is usually done with a ladle. In case of a large kettle, a mechanical agitator is fitted with a motor (Fig.3.4). At the bottom of one of the side of the vat, a drain-valve is provided to drain whey after coagulation.Steam line is equipped with a safety valve, pressure gauge kettle and a water line is provided at the junction of steam line to ensure hot water into the jacket of the vat. To obtain uniform temperature, H-shaped diffuser is provided at the bottom of vat. The vat is provided with over flow line open to atmosphere. This enables release of pressure in the jacket, if any.

ii. Press

After draining the primary whey, the curdled mass is collected in hoops lined with a muslin cloth and weight is applied. In the traditional method, about 45 kg weight is applied for 15-20 minutes to allow secondary whey to drain-off. The matted block is then cut into pieces and dipped in the chilled water. Thus, the paneer is obtained manually in a batch.Continuous paneer/chhana making system is being developed based on the twin-apron conveyor design. In this system operations involved have been mechanized.

iii. Casein Production

Commercial casein is prepared from sour milk. About 2 to 5% milk turns sour during summer due to delay in receiving or processing. To recover some money casein is made. Coagulation vat is used and curdled mass is dried in a dryer. The dried particles are milled in a grinder to make it in powder form.

Dahi and Lassi Making Equipment

Dahi is an indigenous dairy product and well known fermented milk product of India. Dahi is produced by following two processes: (i) Traditional method and (ii) Standardized method.

i. Traditional Method

This is a household method of production of dahi, which is also used in Halwai’s shop. The fresh milk is first boiled, cooled to body temperature and then bacterial culture (also called starter culture) is added to it @ 0.5%. The last step is known as inoculation. Previous day’s Dahi or buttermilk can also be used as starter. After inoculation, it is allowed undisturbed overnight. In case of Misti doi (payodhi), cane sugar is added just after boiling milk. Equipment for production of Dahi, are, Karahi,Khunti (ladle), circular earthenware mould, etc. as required and discussed earlier.

For curd setting, other containers of choice can be used.

ii. The Standardized Method
It is practiced at organized sector of Indian dairy industry. Fresh, sweet, good quality pasteurized milk is heated to 35-40 o C. Then its fat and SNF percentage are standardized. Milk is cooled, then, to 22 o C and inoculated with 1-3% of specific starter culture. The mix is filled in glass bottles or plastic cups and is kept for 16-18 hours at about 30 o C temperature. This is called incubation. After the definite period of incubation, firm curd is formed and acidity reaches to a satisfactory level.Then, the curd is cooled to below 10 o C and stored at about 5 o C temperature. In case of “Misti doi”, cane sugar is added to milk in heated condition. Artificial colour (brown) or sugar-caramel and gur are added.

Equipment required to adopt standardized method of Dahi production are as follows:

Double-jacketed multipurpose vat: As discussed earlier, is necessary for heating milk and addition of milk powder and cane sugar for standardization purpose.Heating or cooling medium flows inside the jacket. Pipeline is attached with it anda drain cock attached to drain the content, whenever necessary. Ladle is used to stir the milk during addition of culture to milk. It is of stainless steel and kept clean.

Incubator: It is needed for setting the curd. It is a closed room or cabinet where temperature 30+5 o Ctemperature is maintained by mechanical means. And the mix (milk+culture) is kept undisturbed for 16-18 hours at that particular temperature to bring about fermentative changes. After the curd is set, the cups are placed in the cold storage.

iii. Lassi Making Equipment
A process vat for preparation of curd is needed. This is a large jacketed vessel,usually vertical tanks having provision for heating, cooling and agitation. These are similar to ghee kettle as shown earlier. In these surface scraping is not required.Hence, the scraper performs as agitator only. Also there is provision for supply of chilled water to cool the product as per the process need. After addition of sugar,the mass is gently stirred to make it in slurry form. This product is, then, filled through an appropriate filling machine.

Khoa Making Equipment

Khoa is a heat desiccated product and made by concentrating whole milk at atmospheric pressure, unlike concentration under vacuum in the milk evaporators.Milk is boiled and evaporated by stirring. The stirring and scraping is done to avoid milk deposits sticking on the heating surface. Initially the scraping is slow as the water content is high and the surface deposition is slow. At final stage, the intensity of scraping increases. The product is taken out in a high viscous and yet flowable form, as it is hot. The cooled mass gets solidified and is called ‘Khoa’.

i. Karahi

Traditionally khoa is made in the open vats, “Karahi” referred earlier. The Karahi offers advantages such as its availability, cost, extent of repair and maintenance,and versatility in use. This can use any heating source like coal, wood or Liquefied Petroleum Gas (LPG). Initially milk has large water content hence agitation/scraping is slow and intermittent. As the concentration increases the fouling of heating surface increases. Hence, vigorous scraping is required. Also the heat intensity is reduced progressively as the water availability for evaporation reduces. All these operations are performed manually and depended on the skill of the operator.

ii. Jacketed Kettle

Hemi-spherical jacketed kettle is shown in figure 3.14. Small entrepreneurs and dairies prefer this equipment. However, this unit has disadvantage of low capacity and the curvilinear profile which causes surface fouling. The scraping of surface,loading of raw milk and unloading of finished product is manual. This unit differs from ghee kettle primarily on the design of scraping mechanism, as the degree of scraping required is more for Khoa during its manufacture.

iii. Conical Process Vat

It is an improved version of Jacketed vessel developed at NDRI Karnal, for its scraping ability and product handling (Fig.3.15). This equipment has straight-line profile of the heating surface, hence, easy to scrap. The scrapers are motorized with speed regulation; hence, scraping speed can be varied in relation to the requirement of the product. Product is loaded from the top while it can be unloaded through an axial discharge mechanism. A batch type Scraped Surface Heat Exchanger (SSHE) is also placed in figure 3.16. This makes about 10-12 kg khoa per hour.

iv. Continuous khoa-making Machine

This machine is developed and perfected to manufacture 50-60 kg of Khoa per hour. An inclined scraper surface heat exchanger has been developed at National Dairy Development Board, Anand. Both of these units prepare khoa @ 45-50 kg per hour from raw milk and 300-350 kg per hour from condense milk. These units are required for large-scale manufacturing of khoa and are used mostly by established dairy plants.

Ghee Making Equipment

Ghee from Makhan (desi butter) is made in a small batch in Karahi. After the water is evaporated and ghee is ready, it is cooled and residue is separated. With the help of a stirrer called Khunti, scraping is done for better heat transfer. This method is not hygienic though common in villages.

i. Ghee Boiler

At an industrial scale of manufacturing Ghee, Kettle. It is a double walled, hemi-spherical or cylindrical shape jacketed vessel. It has provision for steam heating at a steam pressure of 3.5 kg/cm 2 and condensate outlet, safety valve pressure gauge, agitator cum scraper etc. Since there will be deposit formation on heating surface regular scraping at slow speed is required.

There is also a product outlet valve for unloading the finished product. The capacity of this kettle ranges from 50 kg to 1000 kg. There is also one dial type thermometer to indicate the temperature of the jacket. The temperature is varied during preparation of ghee. Same vat or a separate vat may be required for settling the residue and cooling the ghee. For this, agitator is stopped and the product is held overnight and the residue, which settles in, the bottom is filtered out. Ghee is then packed in the polyethylene or plastic pouches or tin-coated cans. Filling and sealing is done manually. For large production, this operation is also mechanized. Suitable filters and cappers are available.

Continuous ghee-making machine has been developed at National Dairy Research Institute, (NDRI), Karnal based on the principle of scraped surface heat exchanger to manufacture ghee from butter. It has capacity of 500 kg/hour and above.

Evaporators and Dryers

We know that the milk has around 85% water; hence, it can be condensed manifolds by reducing the water content for the preparation of special dairy products like condensed milk and milk powders. Milk is normally surplus during winter months,while there is shortage during summer months. By reducing the bulk the shelf life of the milk is also enhanced. This process will help in augmenting the supply during lean months.

i. Milk Evaporators

These are the equipment to concentrate milk usually up to 40% total solids. This
is done by boiling the milk under vacuum. When the milk is boiled under atmosphericpressure, it boils at 100.5 o C. This temperature is so high that most of the nutrients will be lost. When the milk is boiled under vacuum, the boiling occurs at much lower temperature say around 60 o C. At this temperature, most of properties of milk are retained while the water gets evaporated. Milk evaporators are mainly of two types.

Batch-type Milk Evaporator: It is also called as vacuum pan. It is like a storage vat with provision of indirect heating and vacuum. Milk remains in the container for longer duration. Initially, a large amount of milk is loaded and slowly the batch gets concentrated. It is then cooled and stored. Since the evaporation occurs under vacuum the chemical properties of milk remain unchanged and only partial water is removed. Fresh milk is loaded and the heating tubes are submerged. Steam heats tubes are surrounded by milk and vapours formed. A vacuum device removes these vapours. Concentrated milk is taken out from the bottom outlet.

Continuous type: As the capacity of handling increases, there is need to get concentrated milk out in the continuous manner. Also in the batch system, the milk residence time is very high. It does affect the quality of the product. Long tube(rising or falling film) type equipment are available in the market. These units are very tall and sophisticated in terms of their operation and control. The residence time of milk during evaporation is very short, i.e., usually few seconds only. Thus,the product quality is superior. Milk travels from one heat exchanger (calendria) to another in a continuous flow. The flow of milk is such that the velocity of milk is very high giving very high rate of heat transfer. Whole system is under vacuum. Milk flow inside the tube could be either in rising or in falling manner. Accordingly,the evaporator is named. Another way of classifying is, the number of heat exchangers involved. Single, double, triple or even multi-stage systems are available.This helps in economizing the steam consumption. Figure 3.11 shows a classical single effect evaporator. Product enters the heater, and the heated milk is directed into a large calendria for evaporation. The concentrated milk falls into the vapour separator, from where the vapours are either recompressed with help of thermo-compressor or sent into condenser cum ejector system.

ii. Dryers

Drum dryer: It has drums heated internally with high-pressure steam. These drums revolve with low speed in the direction indicated  The milk is supplied through feed pipe. It gets filled in between the drums. A layer of milk gets adhered on the surface of drum and it starts drying till it reaches the knife. The knife scraps out the thin layer and drops the dried flakes into the conveyor. The
dried product is taken out. The vapours generated over drums are sucked out through vapour hood. Milk during drying remains in contact with hot drum for relatively longer, causing denaturation of protein. Hence, powder obtained from this technique usually contains higher sediments. This powder is most suitable for indigenous milk product manufacture such as Gulabjamun. These dryers are getting obsolete due to high-energy requirement.

Spray dryer: They dry partially concentrated milk and are considered energy efficient systems. In this equipment, fine spray of concentrated milk is supplied into a chamber. The spray encounters with hot incoming air. Direct contact with air takes away all moisture from the spray drops. Within seconds the drops turn into a dried powder particle. The particles are heavier than air; hence, they settle down and are collected. The air gets saturated with moisture and is directed towards the exit. While diverting the air, care is taken that milk particles do not get carried away. In this system, the residence time and the rise in temperature of the particle are very less. This reduces the damage to the milk particle. This powder, therefore,gets dissolved in water without much of sediments. Hence, the spray-dried powder is considered excellent for reconstitution purposes. A typical schematic diagram of a spray dryer. Feed (concentrated milk) is sprayed through atomizer. It falls in the drying chamber. The dried product is discharged from the bottom. Fresh hot air is supplied through steam heaters and directed into the drying chamber. The exhaust fan draws the exit air through a cyclone separator. Fine particles carried away, are arrested in the cyclone separator while the clean,saturated air is delivered into atmosphere.

Ice-Cream Making Equipment

Ice-cream and other frozen products manufacturing equipment may be classified as batch freezers, hand operated, kulfi maker, direct expansion type batch freezers and continuous freezers, etc.

i. Hand Operated Unit

It is shown in figure-3.5, has a wooden cylindrical case to accommodate broken ice+salt, a mix can and dasher assembly. The mix-can is made of either aluminum or mild steel with tin coating. This is designed such that it is pivoted in the bottom and has a geared drive system. The dasher remains stationary to facilitate scraper of frozen mass and keep mix moving for better freezing efficiency. This unit is commonly used at domestic level.

ii. Kulfi Maker

Little larger scale operation is through a kulfi maker. In this traditional method, the prepared mix is filled in the metal containers usually cone/square shaped. The size of containers is such that the quantity is served once. These containers are placed in a clay pot or a metallic container, which is large enough to accommodate the broken ice. Salt is added to lower the freezing point, thus causing faster freezing.This type of kulfi maker is very common at entrepreneur level. Care is taken to seal the container to the extent that the brine water does not leak through in the product.

iii. Direct Expansion Type Freezer

The batch freezers are the most common units shown in figure.3.6 and 3.7. These are cylindrical in shape with one jacket for refrigerant and the other for insulation.The cylinder acts as an evaporator of a refrigeration system. It is made of stainless steel.Normally, this is of 6 kg and 12 kg mix holding capacity. After freezing, the volume of mix gets doubled as the air gets incorporated. The mix is agitated by the dasher. The dasher does two jobs, firstly to remove frozen mix from the inner shell and second to agitate the mix such that the mix does not freeze into one solid mass.During agitation a filtered atmospheric or pressurized air is sent into the mix. The air gets trapped causing overrun of frozen mass. This increase in volume is called overrun.

Continuous type freezer: As the scale of production increases over 500kg/h, the continuous or instant freezers are used. The mix is continuously pumped into the freezer cylinder and the frozen mass is discharged from the machine.The principle of freezing is the same, however improved automation and control are necessary. The desired amount of overrun and degree of freezing can be adjusted with these controls. Pumping of mix is half the volume of the ice-cream outlet pump. Similarly, the dasher design is such that the mix flows from one end to outlet without backward flow.

In both the freezers, the frozen mix coming out is in flowable state. It is soft at –10 o Cand served as softy. The frozen product is filled into cups/bricks and put into hardening freezers for hardening and is served to consumers as ice cream. Soft serve freezers or softy plants are like batch freezers where soft frozen mix is directly drawn into edible cones or cups. Once the mix is frozen, the dashers keep rotating and the refrigerant is switched off. This way, the mix keeps in a flowable state and the temperature is between –5 o to –10 o C, no hardening is required.

Butter and Cheese Making Equipment

Butter is the name given by western countries. In India, this product is referred as ‘Makhan’, the country made “desi” butter. The process line at domestic level varies and also the compositional parameters. The Makhan is usually freshly made and consumed. The leftover, if any, is stored for manufacture of ghee. As the cream availability increases, the butter quantity manufacture exceeds the domestic level handling. Cream is, thus, handled through larger containers called ageing vats.

i. Cream Ageing Vat

It performs the batch type pasteurization as discussed in unit-2. This tank has provision to store cream at 4 o C; hence, cream collected is stored overnight,pasteurized and then put into the churn.

ii. Churn

The churns are of cylindrical, conical, dice and top shaped containers .They are made of stainless steel food grade AISI-304. Provision is made for slow revolution with changed direction of rotation. The churns are 1/3 rd to 1⁄2 filled with cream. During rotation the fat particles colloid with each other and form clumps.Care is taken that the temperature of cream/fat is maintained, i.e., the chilled water is sprayed over the churn during summer. The concussion is better achieved if the temperature of cream/ fat remains between 45 to 55 o F. The cylindrical churn will have internal baffle to break the motion of cream along with the cylinder body,while in other shaped churns, such provision may not be required. The churn will have a complete geared drive system to obtain different speeds, water spray mechanism to maintain temperature and guard rail to protect workers. Churn under rotation creates vibrations due to uneven shape and load; hence, proper foundation is essential. To facilitate operation, the churn is provided with an outlet in the form of manhole, buttermilk drain, sight glass, etc.

iii. Butter Trolley
Butter prepared in the churn requires unloading. Hence, a hygienically designed stainless steel open type trolley is required. The size of trolley should be such that it should accommodate all butter from the churn. If the quantity of butter made is less, one may collect butter in other containers, provided they are clean and designed to handle food products.

iv. Continuous Butter Manufacturing Equipment
If the quantity of cream availability further increases, a continuous butter-making machine could be used. Most common and convenient machine is “CONTIMAB”Although there are two other types of continuous equipments available in the market. In this machine all steps required in butter making such as churning,working, salting, etc. are done in a continuous manner. The cream of 30 to 40% richness keeps flowing into a cylindrical churn. The churn delivers clumped fat mass into the working zone, while the buttermilk is drained. During working, the texture modification, moisture regulation, colour addition, salt mixing etc. are obtained.The end product in the form of rectangular slabs comes out of the plant. It is, then,hooked with at appropriate packaging machine.

v. The Cheese Making Equipment
These are cheese vat, knife, curd mill, hoops and press, etc. The cheese vat is used for coagulation and cooking and is made of stainless steel in rectangular shape. This vat is jacketed allowing space for circulation ofhot water between the inner and outer containers. It may or may not have an agitator as shown in the diagrams. During coagulation and cooking, agitator is used for uniform dispersion of coagulant. The whey is drained and the curdled mass is placed in cheese hoops for further matting and drainage of secondary whey. The pressure is applied through a cheese press on these hoops for expulsion of whey,thus, the block of curdled mass is obtained .It is then waxed and stored for ripening.After ripening, cheese of different flavours is prepared for further processing as
per the manufacturing requirements.

Dairy Equipment for Products Processing

We have learnt as to how a dairy plant should be planned for processing of fluid milk, and how selection of various equipment for pasteurized and standardized milk should be done. The usefulness of clarification and cream separation to produce good quality standardized fluid milk has been discussed. Importance of homogenization and in-line filling has been explained. How a fluid milk plant is cleaned without opening the equipment has also been explained in brief. Certain aspects of building construction such as type of flooring, walls, ceiling, ventilation and flies control have also been discussed.

We will learn about equipment required for the manufacture of milk products. Milk products are made in every country and therefore, a simplerclassification is done as western and indigenous milk products. The equipment required for the western milk products like butter, ice-cream, cheese and milk powder will be discussed. The emphasis will be given on small level operation, while a passing reference will be made for large-scale operations. Similarly, indigenous milk products such as ghee, curd, lassi, khoa, etc. will be discussed in detail.

Attempt will be made to compare certain similarities of western and indigenous milk products like Butter Vs Makhan, Ice-cream Vs Kulfi, Cheese Vs Paneer, Curd Vs Yoghurt, etc.

In order to generate interest for readers, some basic principles involved in the manufacture will be discussed. Smaller equipment will need little care and maintenance, while the larger equipment will need more attention. Important aspects of maintenance will be explained along with the discussion on individual equipment.Every equipment has some unique features or specific requirement for its safe and uninterrupted operation. Wherever it is considered appropriate, a brief observation is made so that learner will take care during the selection of particular equipment.Since products vary from place to place and require regional attributes, it may not be possible to recommend any single equipment. After attaining the knowledge, you can select your own manufacturing strategy.

Clean-in-place (CIP) Cleaning System

It is a process that combines high velocity scrubbing and chemical actions of the circulating detergent solutions to remove the deposits from milk handling equipment.The clean-in-place (CIP) system of cleaning eliminates the dismantling and reassembling process for the equipment for the cleaning purposes. This reduces the human effort involved and economizes on labour, time and energy.

The CIP System consists of storage tanks for water, alkali and acid detergents,pumps and interconnecting pipelines for solutions. Pressure jets, perforated spray balls are employed in conjunction with CIP system for creating effective turbulence for proper cleaning of storage tanks

Storage tanks have the provision for heating of the solutions. Equipment to be cleaned is connected with this system and different solutions are circulated through the equipment for a definite period of time in a sequence decided as per the cleaning cycle. The time of circulation, temperature and the concentration of cleaning solutions and the turbulence required for physical action depend upon the type of deposits in the equipment.

Addition of higher amount of detergents or unnecessary increasing the cleaning time does not remove additional deposits from the surface. Also sometimes higher temperatures of detergent solutions may fix the deposits more firmly on the milk process equipment.

The detergent solutions are reused as many time as possible. The concentration of the detergents is constantly monitored. For conservation of water, an additional tank is provided which collects the final rinsed water, which is used for pre rinse in the next cleaning operation. Cleaning of large vessels and storage tanks is not satisfactorily achieved by using circulating system alone.

Packaging and Filling

Milk is filled in bottles and the plastic pouches. The filling in bottle is done under gravity or the vacuum and only fixed volume will be filled. The cleaned empty bottles are placed on the pedestal, which lifts the bottle against the filler valve. As soon as the bottle joins the valve, milk starts flowing into the bottle for a fixed time. After filling, the bottle is lowered and removed from the pedestal and capped. Machine is integrated with the continuous pasteurizer.

Homogenizer and Centrifuges

Homogenizer breaks the fat globules. Large size fat globules have tendency to float and form a cream line on the surface making milk a non-homogenous product.After homogenization the milk globules number increases 10,000 times and the size is reduced 1/10 th of the original, usually less than 1 mm size and hence the tendency of rise of fat globule is considerably reduced. This equipment is also employed for preparing reconstituted milk, ice-cream mix, etc. The main reason is to make a homogenous product.

From technological angle, there are tremendous improvements in the quality of milk and ice cream. In this equipment (Figure-2.9) the milk is passed through a small opening under very high pressure. This generates the velocities of the order 100 to 250 m/s, resulting in high shear stresses. These shear stresses break up the fat globules.

i. Homogenizer

The are various types of homogenizer, based on the type of homogenizing head.Also the operation could be in single stage or in two stages.Two-stage operation is considered most efficient because the sheared globules have little chance of getting mixed again. They remain dispersed. In general the homogenizer consumes very high electrical energy. The initial cost of machine is also high, as the material of construction requires special material, which is very hard and hence, expensive. A homogenizer comprises of a homogenizing head,homogenizer triplex pump, high capacity motor, power transmission mechanism, and  a pressure gauge.

ii. Centrifuges

Fresh raw milk contains fat 4.5% or above. It also gets contaminated with dirt,straw, etc., even leucocytes (udder cells) gets into the milk during milking. Both of these could be removed by centrifugation process.

Cream separator: It is equipment, which operates continuously and imparts centrifugal force to the incoming milk stream. 

Clarifier: It is similar to the cream separator. Its function is to remove extraneous elements such as dirt, chaff and leucocytes cells, etc. These are heavier and the undesirable elements. By centrifugation these particles are collected at the periphery.There is enough space (residue space) provided in the bowl, which accumulates these particles until the unit is stopped and cleaned. In case the residue level is high or the operation is required for longer duration the residue needs continuous removal.Therefore, modern separators have been provided with clarifiers to remove sludge in continuous manner.
 

Cream separator and the clarifier could also be an integrated unit. The modern centrifuge has provision to remove cream or adjust the amount of fat required and also to remove dirt.

Pasteurizer and Sterilizer

i. Pasteurizer
We will now study two types of pasteurizers commonly used in a dairy plant (i) Batch and (ii) Continuous type.

Batch/Holding type Pasteurizer: It is also called as Low Temperature Long Time (LTLT) Pasteurizer. Batch process is mostly preferred where small quantity of milk is handled. In this method milk is generally heated to 63 o C and held for 30 minutes and then cooled to 5 o C or below. Here indirect heating is done by means of hot water.

Continuous type Pasteurizer: The other most common method is High Temperature Short Time (HTST) or Flash pasteurization (Figure-2.8). In this process,milk is heated to above 72 o C temperature for a period of about 15 seconds in continuous manner and promptly cooled. It is a plate heat exchanger type assembly,having different sections such as heating, regeneration and cooling, in a single compact equipment assembly. This type of pasteurizer is equipped with different accessories like float control balance tank (FCBT), filter, pump, hot water mixing battery, flow diversion valve (FDV), temperature indicator and recorder, etc., to ensure uninterrupted flow of milk by continuous operation. Hot water at a 90-95 o C temperature is used as heating medium and chilled water at 1-2 o C temperatures is used as cooling medium. This is energy efficient system but expensive in terms of initial cost.

ii. Sterilizers

In the process of sterilization, all the microorganisms are supposed to be destroyed.The milk is heated to 109-115 o C for 20-40 min, in bottles and in a batch while 135-150 o C for 2-6 sec only in the continuous type of systems for large capacity operations. Sterilized milk is then aspectically filled in sterile containers. This milk can be stored at room temperature for 3 to 6 months. Usually this system is very expensive.

Batch sterilizer: In this sterilizer, milk is filled in the glass bottles and capped.These bottles are placed in baskets or carriage and locked in stationary autoclave.Autoclave is a high-pressure vessel, stationary or mobile, hooked with steam connection on heating. Heat is transferred uniformly in the bottle for better treatment.Also these autoclaves are made to revolve to facilitate faster heating. It takes little long to bring the desired temperature. Thereafter, the temperature is maintained for 20-40 minutes to achieve sterilization. After this holding, the steam/condensate is drained and bottles are allowed to cool slowly. Final temperature of the bottle/milk is brought down to 30-36 o C. The sterilizer has thermometer, steam pressure gauge,convenient loading and unloading provision. For better results, these instruments should be maintained properly.