48 Chapter 2
bovine milk has been diluted with water
using a cryoscope. If so, the freezing point
increases. The freezing point of fermented
milk, goat, and sheep milk is signifi cantly
lower than that of bovine milk.
Similarly, the boiling point of milk is
100.17 ° C, which is higher than that of pure
water due to the dissolved components
lactose, sodium, potassium, and chloride.Density
Density is the mass/unit volume expressed as
g/cm^3. The density of milk at 20 ° C ranges
from 1.027 to 1.033 g/cm^3.
The density is infl uenced by various
factors including temperature and total solid
concentrations. An increase in fat content or
temperature results in a decrease in density;
conversely, an increase in solids - not - fat
content results in an increase in density. The
solids - not - fat concentration, fat concentra-
tion, and density can be calculated if two
factors are known, as well as the total solids
percentage.
Density is useful to convert volumetric to
gravimetric measurements and in the produc-
tion of cream. The density of fat is lower than
that of the other constituents in milk, which
ultimately causes the fat portion to rise to the
surface of the milk when it is left undis-
turbed. Mechanical separators are used to
separate the cream portion from milk.Specifi c Gravity
Specifi c gravity is determined by the ratio of
mass of a solution or substance to the mass
of a similar volume of water. The specifi c
gravity of whole milk is between 1.030 and
1.035, averaging 1.032. The specifi c gravity
of milk is used to determine the amount of
non - fat solids and the addition of water using
a lactometer. The addition of water lowers
the specifi c gravity. The addition of sugar or
milk solids in yogurt and ice cream dairyindex, followed by proteins, lactose, and
other minor constituents.
Flavor
Taste and aroma infl uence the assessment of
a quality product to consumers. Milk has a
clean, pleasantly sweet fl avor; however, it is
bland and the presence of off fl avors is very
noticeable. Off fl avors can occur by contami-
nation of microorganisms, processing condi-
tions, and undesirable chemical or biochemical
reactions.
Colligative Properties
Colligative properties depend on the number
of dissolved particles, particularly lactose,
and the dissolved salts including sodium and
chloride in solution, rather than their proper-
ties. Colligative properties include freezing
point, boiling point, and osmotic pressure.
Osmolarity and Osmotic Pressure
Osmolarity is the total number of particles in
a given volume of solution expressed as
osmol/Kg. The osmotic pressure of milk is
approximately 700 kPa (7 bar), which is
infl uenced by the salt and lactose content of
milk. It is the same as the osmotic pressure
of blood. Osmolarity is proportional to the
freezing point of milk and the osmolarity of
infant formulas is controlled to resemble the
osmolarity of human milk.
Freezing Point and Boiling Point
The freezing point of milk is − 0.540 ° H
( − 0.521 ° C), which is lower than the freezing
point of water. This is principally due to the
presence of dissolved components such as
lactose, sodium, potassium, and chloride.
The freezing point is the same for products
derived from milk including cream, whey,
and skim milk. It is used to determine whether