Figure 1-3. Milk flow through a HTST pasteurizer (typical temperature).
a. Raw Milk Storage. Raw milk is received at the pasteurization plant at a
temperature of 45F (7C) or less and pumped into raw milk storage tanks (see block 1,
figure 1-3). This raw milk must be maintained at 45F (7C) or less until processed.
The steps in processing raw milk will vary at different processing plants and the type of
equipment used will also cause a variation in the processing steps. Raw milk that is to
be packaged as whole milk is normally clarified, homogenized, pasteurized, and cooled
prior to packaging. The sequence of these steps is not always in the same order. If the
batch (vat) pasteurizer is used, the raw milk may be clarified and homogenized prior to
pasteurization. These steps may also be accomplished after the milk is pasteurized.
b. Clarifier. Clarification is a mechanical means of removing foreign matter,
such as dirt, hair, manure, and blood cells from milk. The clarifier (see block 2, figure
1-3) operates on the principle of centrifugal force. It consists of a bowl and a series of
cone-shaped discs enclosed within the bowl. As the bowl revolves at several thousand
revolutions per minute, the foreign matter, being heavier than the milk, is deposited on
the inside walls of the clarifier bowl in the form of slime. This clarifier will not always be
located at the same place at all pasteurization plants. The milk may be clarified
immediately after it is pumped from the raw milk storage tanks and prior to entering the
pasteurizer; it may be clarified after it is heated in the regenerator section (HTST); or it
may be clarified after pasteurization and/or cooling. Some milk plants often use a
standardizing clarifier. This piece of equipment can be used as a clarifier, separator,