Processing Principles of Dairy Ingredients 105for material balance calculations and for
determination of losses occurring during pro-
cessing and packaging. The freezing point of
milk test determines adulteration with water,
whether accidental or intentional. Adulteration
of milk is a prosecutable offence.
The most common procedure is to record
the volume of milk delivered by a tanker.
Volumetric measurements involve a volu-
metric fl ow meter fi tted with an air elimina-
tor. Presence of air can distort readings of the
volume of milk. The milk passes through the
air eliminator and a fi lter into the metering
device prior to going to storage silos. In some
dairies, rather than recording the milk volume
the tanker may be weighed prior to emptying
and after discharging its load.
After discharging its load of milk, the
tanker is cleaned in the reception bay or a
special cleaning bay. The inside of the tanker
is washed by a cleaning - in - place system that
rinses the tanker, cleans it with detergents,
rinses the detergents, and sanitizes the tanker.
The exterior of the tanks also is often washed
so that the tankers always look clean on the
road. After cleaning and sanitizing the tanker
goes to its next round for milk collection.
The raw milk is stored in large vertical
tanks known as silos (Figure 4.3 ). These silos
can have capacities of 25,000 to 150,000
liters (6,000 to 37,000 U.S. gallons). The
silos are placed outside the dairy with an
inside outlet bay. They have double wall con-
struction with an outside welded sheet metal
wall and a stainless steel tank within. The
silos have methods of agitating milk to
prevent gravitational fat separation.
The agitation must be very smooth to
avoid rupture of the milk fat globule mem-
branes, which can cause lipolysis of milk fat.
Lipolysis generates off fl avors and odors.
The most common agitation system is a pro-
peller agitator. The tanks contain instruments
including a thermometer, level indicator, low
level protector, overfl ow protector, and empty
tank indicator. Modern dairies have electron-
ically transmitted data on temperature, levelsStorage of Raw Milk
The milk tanker enters a covered special
reception area at the dairy. A technician from
the quality assurance department checks the
temperature of the milk and draws a repre-
sentative sample. The technician also checks
the odor of the milk and records whether any
off odors are detected. The representative
sample collected from each tanker is ana-
lyzed for sediments, antibiotic residues,
somatic cell count, bacteria count, protein
and fat content, and freezing point. Some
dairies also may conduct a direct microscopic
count of the bacteria present in the milk. The
normal bacteria and coliform counts take 24
to 48 hours. The results of the remaining tests
are available within 15 to 20 minutes. If all
tests meet the standards set by the dairy the
milk is unloaded from the tanker.
Sediment tests point to the quality of milk
production at the farm. Antibiotic tests indi-
cate whether milk from sick animals was
commingled with milk from healthy cows. If
such commingling occurs the entire tanker
load of milk is rejected. Presence of antibiot-
ics in milk poses a two - fold danger. First,
antibiotic - sensitive individuals can suffer
from consuming tainted milk. Second, anti-
biotics may pose a barrier for acidity devel-
opment in the manufacture of cultured milk
products by inhibiting the starter culture
growth.
Somatic cell counts are indicative of
general animal health. If they are below
500,000/mL of milk the animal herd health is
considered good. If the count exceeds 1
million/mL it suggests the presence of mas-
titis in one or more animals in the heard.
Mastitic cows are often treated with antibiot-
ics; the milk from such animals is generally
discarded on the farm while the cows are
receiving the treatment and for a period
afterward.
Protein and fat contents are used to deter-
mine payments and to gain full accounting of
the raw materials received. This is important