(2) Sediment test. A sediment test may be performed on the platform. This
test is made by filtering one pint of the raw milk through a special cotton linen disc and
comparing the results with a set of standard discs that represent all degrees of
cleanliness.
(3) Laboratory tests. Laboratory tests consist of more complicated physical,
chemical, and bacteriological procedures. Some of the tests included here are the
acidity test, the direct microscopic test, a standard plate count, the resazurin test, the
methylene blue test, and coliform tests.
b. Determining Amount Delivered. One method for determining the amount of
milk delivered is to use a calibrated measuring rod. The rod is submerged in the
delivery tank and the amount of milk delivered is determined by where the milk line
appears on the calibrated rod. The standard method today is to measure the raw
product being received by use of a meter gauge. Milk pumped from the delivery vehicle
and passes through a gauge that measures the milk in gallons.
c. Transferring Milk from Carrier to Plant. Milk from tank trucks is pumped
into receiving tanks. Maintaining proper sanitary standards of the transport vehicle,
receiving area, and storage tanks is extremely important.
d. Storage of Milk. Milk is usually stored in storage tanks prior to being
pasteurized or other processing. The milk is cooled to 45F (7C) or lower and
maintained at that temperature in the insulated storage tanks. These tanks vary in
capacity from 100 to 40,000 gallons. Milk processing includes clarification,
standardization, separation, homogenization, and pasteurization, followed by cooling
and packaging.
1-13. CLARIFICATION
The purpose of clarification in processing milk is to remove heavy sediment
particles and foreign materials by mechanical means; namely, centrifugation. This can
be done with either cold or warm milk; however, warm clarification is more efficient. The
centrifugal clarifier consists of an enclosed bowl and any number of cone-shaped discs
which rotate at a high rate of speed causing a centrifugal force. Milk is pumped into the
bowl, subjected to the centrifugal force, and then pumped out. The force throws the
foreign materials and heavy sediment to the walls of the bowl where they remain until
the clarifier is cleaned. The material removed from the milk includes visible dirt, blood
cells, hair, fragments of udder cells, and slime. Clarification cleans milk; it does not
purify it or remove any bacteria.
1-14. STANDARDIZATION
Standardization is the process of raising or lowering of the percentage of milkfat
in milk or cream to attain the desired standard. In order to minimize contamination of
the finished product, standardization should take place prior to pasteurization. Raw milk
MD0715
1-11