Treatment of milk for cheese making
Clarification may be as simple as filtering out debris or may include standardization of micro flora by removing microbial cells and spores. The principal clarification/standardization procedures are as follows.
(1) Cloth filters are common to remove debris at the farm but should not be necessary at the processing plant.
(2) Centrifugal clarifiers, medium speed centrifuges, remove particles which escape filtration. Cream separators effectively double as centrifugal clarifiers because small particles of debris collect at the periphery of the separator bowl and are ejected as sludge. The loss of milk solids by this process is minimal.
(3) Bactofugation is a high speed centrifugal process which separates bacterial cells and spores. This process is particularly important in Europe where problems arise due to spore formers such asClostridium tyrobutyricum.
- Bactofugation removes 95% of the spores of milk which means the risk of late gas defect due to germination and growth of Clostridium tyrobutyricum is much reduced but not eliminated.
- 1-2% of milk solids is transferred to the bactofugate which, in particular contains casein along with somatic cells and bacteria. To avoid yield loss the bactofugate which contains 12-16% of dry matter, is sterilized by ultrahigh temperature processing and added back to the milk.
(4) Microfiltration is a membrane process which has been used in a few European cheese plants since 1985. Think of microfiltration as an ultrafine sieve. Microfiltration and related membrane processes are illustrated in Figures on the right and below and are further described in Cheese making from ultra filtered milk. Microfiltration achieves about 99% reduction of spore forming bacteria relative to 95% by bactofugation. The disadvantage is that microfiltration can be applied only to skim milk because the milk fat globules are too large to pass through the microfiltration membrane (See the figure below).