Bacteria, especially heat-resistant spores, have a significantly higher density than the milk and consequently are efficiently separated by passing through a Bactofuge®.

In modern self-cleaning separators with a sludge space outside the disc stack, bacteria and spores can be collected over a period of time and intermittently discharged at preset intervals.

Second-generation milk bacteria centrifugal clarifiers are of two types:

  • 1) The “two-phase” has two outlets at the top: one for continuous discharge of bacteria concentrate (bactofugate) via a special top disc and one for the bacteria-reduced phase.
  • 2) The “one-phase” has only one outlet at the top of the bowl for the bacteria-reduced milk. The bactofugate is collected in the sludge space of the bowl and discharged at preset intervals.

The bactofugate from the two-phase clarifier may account for about 3% of the feed, while the corresponding amount from the one-phase clarifier can be as low as 0.15% of the incoming milk. A recirculation system on the two-phase clarifier allows lower product losses (0.05%-0.1%) and higher efficiency in bacterial removal.

Bactofugate always has a higher dry matter content than the milk from which it originates because some of the larger casein micelles are separated out together with the bacteria and spores. The amount of protein in the bactofugate increases with increasing bactofugation temperatures, the optimal being 50°-60°C.

There are two possibilities for positioning the Bactofuge, each one with advantages and disadvantages: before or after the separator. In the first case, the bactofuge works better at constant flow, and the cream coming from the skimmer has a lower bacterial content. But the discharge frequency is higher and the efficiency in bacterial removal is not the highest possible.

According to the chosen positioning of the couple bactofuge/separator, the process temperature and the microbiological quality of the milk, the efficiency obtainable in bacterial removal may be 75% to 95% in TVC, 97% to 99% in anaerobic spores, and 85% to 95% in aerobic spores (SPX, 2015).

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