PROCESSING THE MILK

Filtration / Clarification

Before processing, the cheese milk is clarified / filtered in order to remove certain contaminants such as cellular material, straw, hairs, soil etc. Generally cloth filters are used but clarifiers using centrifugal force called bactofugation, has the advantage of removing spore forming bacteria (Clostridium), thereby preventing late blowing defect and butyric acid fermentation in cheese.

These defects are very common in brined cheeses such as Emmental, Grana Padona, Provolone, Donbo and Gouda. The following preventive measures can be taken to avoid the clostridial spore activity in cheeses.

Bactofugation

The bactofugation is the process of subjecting the cheese milk to high-speed centrifugal force in the clarifying bowl, which is somewhat similar to the cream separator and results in the removal of 99 % of bacteria which is originally present in the milk.

The bactofugate, which is nothing but separated fraction amounting to 2-3% of total milk volume, is removed and sterilized by steam under high pressure (130 – 140°C for few seconds) and then cooled and added to the main lot of milk.

Nitrate Addition

The procedure for bactofugation may not be possible for all the cheese makers and thus requires some other alternative methods. That is addition of sodium or potassium nitrate to the cheese milk in order to prevent the growth of gas forming butyric acid bacteria.

Generally sodium nitrate is added to the cheese milk at the concentration of 70 – 80 g per 500 litres of milk. But the problem with the addition of sodium nitrates (saltpetre) is production of colour defects due to reaction of tyrosine with nitrite and has limited use. Further use of sodium nitrate is restricted in many countries.