Physical Treatments of Cheesemilk
Bactofugation and microfiltration of cheesemilk can be included as a part of milk pretreatment, especially in the manufacture of hard and semihard cheeses where consumers want to avoid the use of nitrates or lysozyme as preservatives.
As was discussed in the section “Market Milk" bactofugation is a process in which a specially designed hermetic centrifuge, the Bactofuge®, is used to separate bacteria, and especially the bacterial spores, from cheesemilk.
The concentrate (bactofugate) which contains both spores and bacteria in general may amounts up to 3% of the feed to the Bactofuge.
In applications where quality milk for cheese is the objective, the Bactofuge is installed in series with the centrifugal separator, either downstream or upstream of it.
Bactofuging milk once is not always sufficient, particularly at high spore loads in the milk.
Without any mechanical means of reducing spores it is normal to add some 15 to 20 grams of sodium nitrate per 100 liters of milk to inhibit their growth, but with single bactofugation and a high load of spores in milk, 2.5 to 5 grams per 100 liters of milk will prevent the remaining spores from growing.
With double bactofugation, reduction of Clostridia spores can reach more than 99%.
Figure 188.8.131.52 illustrates a plant with two one-phase Bactofuges in series serving one sterilizing unit (TetraPak Engineering, 2014).
According to local legislation and to the variety of the cheese, bactofugate can be high-heat treated separately and eventually added to the cheesemilk.
Figure 184.108.40.206 Double bactofugation with optional steriliser (TetraPak Engineering, 2014)
- 1) Pasteuriser
- 2) Centrifugal separator
- 3) Automatic standardization system
- 4) One-phase Bactofuge
- 5) Infusion steriliser, option
Double bactofugation is sufficient in most cases to produce cheese without the addition of bacteria-inhibiting chemicals. During periods when very high loads of spore- formers are expected, small amounts of chemicals (e.g., nitrates), 2.5 to 5 grams per 100 liters of milk, may, however, be used for safety if legally allowed.
The same considerations apply to microfiltration, where the retentate can be sterilized separately if it is allowed to be included in the cheesemilk. Due to the high bacte- ria-reducing efficiency, microfiltration may allow the production of hard and semihard cheese without the addition of nitrate at a level of 15g/100 kg of milk to prevent late blowing by Clostridia spores, if the cream is properly heat treated, with positive consequences for the environment, quality of resulting whey, and consumer health (Meershon, 1989).