Grading of milk

Grading of milk

Grading of milk at collection centres
Following criterion, based or organoleptic tests may be used for grading of milk at the
rural milk collection centre.
Flavour : 45
Sediment : 10
Cleanliness of container and closure : 5
Temperature : 5oC

Milk reception at chilling centre
In a distant milk plant, rurally collected milk is first brought to a common chilling centre.
In view of the high ambient temperatures prevailing in the tropical climatic conditions in India, it
is imperative to chill and milk to 4oC and transport it at the same temperature to the milk
processing plant. The chilling centre may be operated by dairy plant directly or by the
contractor, in accordance with the prevailing situations.

The collection of milk from the chilling centre usually takes place once a day. At the chilling centre, milk is promptly chilled to 4oC and stored in large tanks of 2,000-10,000 litre capacity. Chilling centre operation is economical only when about 30,000 litre of milk is handled per day. It is then transported, though tankers, to dairy processing unit.

Following equipment are used for chilling of milk:
Surface cooler : (Direct expansion type, ice bank and brine)-for handling up to 5,000 litre of
Plate cooler : This is suitable for handling more than 30,000 litre of milk.

Grading of milk at chilling centre.
Smell : 45
30 MBR test : 35
Sediment : 10
Container/Closure : 5
Temperature : 5oC

Titrable acidity, clot on boiling test, alcohol test, and alcohol alizarine test may be done
on suspected samples of milk for confirmation.

Milk reception at dairy plant
The milk at the dairy plant is received either in cans or road/rail tankers. There are
separate reception docks where milk is received through tankers and cans. Milk reception dock
is designed for unloading the cans directly on the platform. Milk cooled in cans is brought to
the dairy in trucks/lorry from where the cans are unloaded onto a conveyor
The milk from each can is automatically or manually emptied into a weighing bowl, that
indicates the quantity, which is recorded by the operator. The empty cans are further conveyed to
can washer where they are automatically washed with detergent and hot water and steam
sterilized to be made ready for next collection trip.

The milk from chilling centre is usually transported in tankers to the dairy. Milk received by tanker can be measured by weight or by volume. Generally the milk from the tanker is measured by volume. A flexible line is connected between the tanker milk delivery pump and flow meter installed at the reception dock.

milk is pumped through the flow meter into large vertical storage tank (25,000-1,50,000 litre capacity) called ‘Silo’. The flow meter continuously indicates the volume of milk received. Alternatively, the tanker can be weighed before and after unloading to know the amount of milk received at the dairy. This is also possible by using special tanks fitted with load cells that supply electric signal, which is proportional to the weight of the tank. The weight of the contents in the tank can be recorded after all the milk is delivered. The milk is then pumped into the silo.
Preservation of raw milk.

In order to produce milk products conforming to international quality standards, it is
important that the milk is collected, transported and cooled immediately under strict hygienic
conditions. Ideally, all the milk reaching to the dairies should be bulk cooled.
Under tropical conditions, it would be beneficial to have access to methods, other than
refrigeration, for retarding the bacterial growth in raw milk during collection and transportation
to the dairy plants. However, whatever method is adopted it should not have harmful or
toxicological effects.

Further, the main objective of the method should be to maintain food safety and not otherwise. One of the methods, which has some merit and is worth considering, is LP system (Lactoperoxidase/thiocynate/hydrogen peroxide system). The LP system is an indigenous anti bacterial system in milk and human saliva. The enzymes lactoperoxidase is present in cow and buffalo milk in relatively high concentrations. The anti bacterial effect of the LP system is mediated by short-lived oxidation products of thiocynate. To activate the LP system
is milk, adequate concentrations of thiocynate and hydrogen peroxide are added. The optimum
way of applying LP activation has to be decided from case to case basis, but it is quite feasible
that the required concentration of hydrogen peroxide, the thiocynate are converted in the form of
tablet which is sufficient for one can of milk. It is very important that preservation of raw milk
by LP system is controlled at the society level and the individual farmers do not have direct
access to such chemicals.

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