Skimming milk and whey
Milk skimming process
Raw milk of known fat content, free from air, should be fed to the milk separator at relatively constant temperature and capacity. A change in operating conditions will influence the skimming efficiency. Standardized cream and skimmed milk are the products leaving the separator.
Sediment discharged from the centrifuge during separation may contain bacteria, leucocyte, hair, sand and similar. If the hot milk separator is the first centrifugal clarification step in the dairy, the discharged sediment is not possible to recycle. The best way to dispose it is to sterilize it with steam and dump it.
Whey skimming process
For an efficient separation of fat most of the remaining cheese fines have to be removed before separation. Fines can be taken away by sedimentation in tanks, by filtering or by centrifugal clarification. Whey, free from air and preferably from fines, should be fed to the separator, at relatively constant temperature and capacity. A change in operating conditions will influence the separation efficiency. Whey cream and skimmed whey are the products leaving the separator. Sediment discharged from the centrifuge during separation consists of
residual cheese dust and precipitated whey proteins. The best way to dispose it is to send it back to the farmers.
With efficiency for a separator, we normally mean the ability to reduce the fat content in milk. But we can also define the performance in terms of the possibility to produce cream with a consistent and high fat content, or a production with no unintentional stops.
For standardization of milk, fat content in skimmed milk is of less importance because part of the cream is re-mixed to get the proper fat content in the standardized milk. For this reason, you may standardize at a higher capacity than used for skimming.
The product quality in a milk separation process is most often measured in terms of free fat and air in the discharged products. The temperature for crystallization and melting of milk fat range from 17-38°C. Therefore, it is important to heat the milk to about 45°C before separation, to be sure not to
damage globules with partly melted fat. Free fat causes two serious faults, sticking and clumping. Rancid flavors may also develop as a result of lipolytic reactions. If the incoming milk contains too much air there will primarily be a problem with cream control and foaming in product tanks. Secondarily, air is the major cause for destruction of fat globule membranes. The membranes may repair themselves again, but the globule is smaller and free fat has occurred. Smaller globules mean more fat in skimmed milk.