Storage of Processed Milk

While designing a milk plant, adequate amenities must be provided for storing packaged milk in terms of area as well as facilities such as refrigeration. Space would also be required for storing packaging materials, whether they be empty bottles and crates or rolls of packaging films.

 

 i. Storage of Bulk Milk

Insulated tanks: Bulk milk after processing, is stored in insulated storage tanks in the dairy till transportation. The milk remains in the chilled condition. It is recommended that milk be transported to the place of delivery as soon as possible.However, due to limitations in infrastructure milk is stored for periods ranging from 4 to 12 hours after processing.

Storage in cans: Processed milk for bulk supply is also sometimes stored in cans.Since the beginning of the second half of last century aluminium milk cans have replaced mild steel cans that were used earlier. The most common are cans with lids which do not require rubber gaskets for sealing. An adequate sealing arrangement is achieved with sunken grip or mushroom lids. Lids attached to the cans by chains are no longer used owing to problems in mechanical washing. Lead or other seals can be applied through simple arrangements at the lid ring to avoid tampering and pilferage. Normally floor conveyors are used to transport cans from one place to another in the processing area of the dairy plant.Full cans are stored in one layer, thus permitting about 320 to 360 litres of milk to be stored per square metre excluding movement and working space. Empty cans,after washing, are stacked in layers horizontally, up to a height of 1.5 m. For storing and moving washed empty cans simple trolleys on which the cans can be stored in 4–5 layers are very useful. For example, about 20 cans each of 40 litres capacity can be stored on trolleys about 1.7 × 0.7 m with a supporting frame made of a 1/2" pipe.

 

ii. Storage of Milk Packed in Multiple-use Packages

Storage in bottles: Bottles with wide necks (36 to 40 mm), suitable for sealing with aluminium foil caps are most commonly used for packaging of pasteurized milk in multi-use containers. The filled bottles are placed in plastic crates. These were earlier made of galvanized steel wires or strips, but plastic is in vogue these days.The crates have internal divisions so that the bottles are not in contact with one another to minimize risk of breakage. They are designed to interlock, so that a stable stack can be built. Crates with filled bottles are stacked five and six high for one-litre and half-litre bottles respectively for manual handling. Two to three crates more can be put in one stack for empty bottles. Crates can generally hold twenty half-litre and twelve to fifteen one-litre bottles. The stacks can be moved manually or by hand trolleys.

Bottles used for in-bottle milk sterilization have narrower necks (26 mm) than the pasteurized milk bottles so that a more effective seal can be made. Prefabricated crown seals are used to seal the bottles. The requirements with regard to sturdiness during mechanical and thermal shocks are higher than those of a pasteurized milk bottle. The bottles are packed in crates as is done for pasteurized milk bottles. The stacking system and the resulting storage area required are also similar. As with pasteurized milk, dimensions differ from country to country but a neck diameter of 26 mm is universal.

 

 iii. Storage of milk packed in single-use packages

The common feature of single-use containers is that they are discarded after emptying. This fact has an important bearing on the milk plant construction,organization and on the economics of the whole business. There is no collection and washing of the milk packages. Only the crates that carry the filled milk packages are collected and washed. Single-service delivery wraps, trays or boxes may also replace these. Intermediate storage of packing material and filled packages has to be organized at the plant.

Storage in pouches: The pillow-shaped sachets of pasteurized milk are collected in tubs after they are cut and separated from the packaging machine. They are placed in rectangular plastic crates holding 20 packages each and the crates are then stacked.Thus with crates stacked 10-high containing 1/2-litre sachets the store capacity without space for entry, movement and working is about 500–600 1/m2.Both 1-litre and 1/2-litre packages have the same width and thickness (0.09 m).Varying the distance between transverse seals facilitates changing the capacity. It is important that the film is free from pinholes so as to avoid leakage, particularly when subjected to pressure from the adjoining pouches in the crates. Below Table illustrates the general details and space requirement for storage of film rolls used for pouch filling.

Space requirement for storing film rolls for milk sachets*

Storage in cartons: In several countries, pasteurized milk is packaged in cartons on similar lines as UHT-milk.Rectangular cartons are normally used for UHT milk, though this is not a strict regulation. The tetrahedral packages, after filling, are placed in hexagonal plastic crates holding 18 cartons each. The crates are then stacked normally 6-high as illustrated in Fig. 11.6. Thus with a 6-high stack of crates containing 1⁄2- litre cartons, the storage capacity excluding the area required for entry and working is about 500 1/m2.Empty crates for tetrahedral cartons are normally stacked 15-high. The crates occupy less space when empty, as they are tapered. Rectangular crates occupy the same space empty or full. below Tables give the space requirements for storage of packaging material for tetrahedral and rectangular cartons, respectively.The quantity of raw stock to be stored depends on the location of the milk plant and the paper supplier and also the purchasing power of the producer. It is generally necessary to carry two to three months’ stock.

 Storage space requirement for paper rolls for tetrahedral
milk cartons*

Storage space requirement for paper rolls for
rectangular milk cartons*