and standardizer. Cream may be separated from whole milk, leaving skim milk. When
the butterfat percent of milk is higher than desired, the milk may be standardized (the fat
percent adjusted by adding skim milk) to the desired fat percent.
c. Balance or Float Tank. From the raw milk storage tank, the milk is pumped
into a balance or float tank (also referred to as constant-level supply tank) (see block 3,
figure 1-3). The balance tank is equipped with a float valve that keeps the milk at a
constant level and maintains a constant supply for the pasteurizer, as well as for other
steps in processing.
d. Regenerator (Heat Exchange Section). From the balance tank, the cold
raw milk is drawn into the regenerator section (see block 4, figure 1-3) of the HTST by a
displacement timing pump. The timing pump is located at the exit of the regenerator
section, which accounts for the principle of the raw milk being drawn or sucked into the
regenerator. In the regenerator section, the cold raw milk is heated to approximately
135F (57C) by hot pasteurized milk flowing in a counter direction on the opposite
sides of the thin stainless steel plates. (This hot pasteurized milk is also cooled to
approximately 90F (32C) by the raw milk.) The pressure in the pasteurized side of the
regenerator is always greater than the pressure on the raw milk side, which eliminates
the possibility of contaminating the pasteurized milk with raw milk if flaws or leaks
develop in the plates and gaskets.
e. Timing Pump. The positive displacement timing pump (see block 6, figure
1-3) draws the raw milk out of the regenerator section and pumps it under pressure
through the rest of the HTST pasteurization system. The timing pump regulates the
flow of milk through the final heater, holding tube, regenerative cooler, and final cooler.
The pump must be regulated and controlled so that it will take 15 seconds for every
particle of milk to flow through the holding tube of the HTST pasteurizer.
f. Homogenizer. It is a common practice to connect the homogenizer (see
block 6, figure 1-3) between the timing pump and the final heating section of the HTST.
(The clarifier may also be installed after the homogenizer and prior to the milk being
pumped into the final heater.) In the homogenizer, the fat globules of the milk are
reduced in size as the milk is forced between small openings under pressure ranging
from 2,000 to 3,000 pounds per square inch. The breaking up of the fat globules allows
them to be evenly distributed throughout the milk and prevents the formation of a cream
layer. The Grade A Pasteurized Milk Ordinance defines homogenized milk as "milk
which has been treated to ensure breakup of the fat globules to such an extent that,
after 48 hours of quiescent storage at 45F (7C), no visible cream separation occurs on
the milk, and the fat percentage of the top 100 milliliters of milk in a quart, or of
proportionate volumes in containers of other sizes, does not differ by more than 10
percent from the fat percentage of the remaining milk, as determined after thorough
g. Final Heater. From the homogenizer, the milk is pumped through the heater
section (see block 7, figure 1-3) of the HTST pasteurizer. The milk, already preheated