Yields

i) Actual yield : Actual yields of casein are usually considered as kg of casein bagged per 100 kg of skim milk. This is used as a measure of the processing efficiency. The accuracy of yields depends on:

•  the frequency of measuring – weekly, monthly, etc.
•  comparison with yields at the same time in previous seasons  relationship to the theoretical yield
• The percentage of casein in the skim milk varies with the fat content of the whole milk, type and time of the season depending on feed available, and between different areas.

 ii) Quantity of skim milk: This can be measured by the formula given below:

W = [(C-M) / (C-S)] x 100

Where, W = weight of skim milk per 100 kg of whole milk

C = fat content of cream

M = fat content of milk

S = fat content of skim milk

iii) Theoretical yield: Assume a casein composition of: 85% casein; 10-12% moisture; 2-4% other milk solids and a skim milk casein content of – 2.8% Then theoretical yield per 100 kg skim milk

= 100/85 x 2.8 = 3.3%

 % Fat in milk % Casein in milk% Casein in skim milk % Yield from skim milk

The theoretical yield for different fat contents in 

whole milk

iv) Processing factors affecting yield: A high production of fines will result in a reduced yield. Fines production is increased by:

– over acidification or uneven precipitation of curd

– inefficiency in acid-skim milk mixing

– low cooking temperatures

– excessive pumping or agitation of curd

– over acid or alkaline wash waters.

These factors may account for fines losses of up to 10% of expected casein yield.Some degree of fines recovery is possible by the use of hydro clones or settling techniques. However, there is no substitute for correct processing procedures.

Over drying of casein can cause substantial reduction in the expected yield. Casein should not be dried to levels excessively below those specified by the market.