Concentrated Fluid Milk Ingredients 131After addition of sugar, the fat and total
solids content of the product is re - adjusted to
desired levels to meet minimum standards.Lactose Seeding
Next, lactose crystallization is induced.
Although the concentration of sugar in mois-
ture is above 61%, osmophilic organisms can
grow. Because part of the lactose contained
in the product may be over saturated, auto-
crystallization of lactose may occur and
lactose may appear as large crystals with a
size greater than 15 μ m. The presence of
large crystals results in a defect known as
sandiness, i.e., a gritty mouth feel when SCM
is consumed. To avoid sandiness, the concen-
trate is cooled to the optimal seeding tem-
perature of approximately 25 ° C to 30 ° C
(77 ° F to 30 ° F) and inoculated or seeded
with fi ne milled and pasteurized dry lactose
crystals to promote instant and controlled
crystallization. Below 20 ° C (68F ° F), lactose
crystallizes instantly without seeding. At
30 ° C to 50 ° C (86 ° F to 122 ° F), less lactose
crystallizes and above 50 ° C (122 ° F), lac-
tose is in solution and does not crystallize.
The amount of lactose added is equivalent to
0.5 kg/1,000 kg milk. The smallest possible
size for the seed lactose should be less than
10 μ m with a signifi cant portion less than
1 μ m. Rapid cooling and agitation occurs
during seeding. The amount of crystals
formed is more than 4 × 1 0^11 crystals/m^3.
Lactose crystal size affects viscosity of SCM.
During the fi rst half of crystallization, the
viscosity of SCM increases to a maximum
because of small crystal size but as crystal
size grows, viscosity decreases.
After crystallization is complete, the prod-
uct is packaged by fi lling tin cans that have
been previously sterilized by fl aming. It is
important that the air in the fi lling area is clean
and fi ltered to avoid future microbial quality
issues. Furthermore, the fi lled can must have
the lowest possible air space (head space)
above the product to prevent mold growth.age thickening during storage. In general,
low heat treatments favor increased viscosity,
whereas high heat treatments give lower vis-
cosity in SCM. Heating at 80 ° C to 85 ° C
(176 ° F to 185 ° F) for 15 to 25 minutes gives
the desired initial viscosity with slow age
thickening. Viscosity should be suffi cient to
prevent separation during storage and age
thickening; the product should remain pour-
able during storage. The average viscosity of
SCM is approximately 2 Pa.s, about 1,000
times the viscosity of milk. The heated milk
is homogenized at low pressure (approxi-
mately 2 to 6 MPa) because creaming is not
often a problem in SCM.
The heated product is then condensed by
evaporation under vacuum at 65 ° C to 70 ° C
(149 ° F to 158 ° F) in a multiple - effect evapo-
rator. Reverse osmosis may also be used to
concentrate the milk. Condensation tempera-
tures lower than 65 ° C (149 ° F) favor germi-
nation of spores and growth of heat - resistant
bacteria. The concentrated product is then
cooled to 20 ° C to 30 ° C (68 ° F to 86 ° F) using
vacuum coolers.
Because SCM is not heat sterilized, the
addition of sugar serves improves its keeping
quality by providing a bacteriostatic environ-
ment. Sucrose is the preferred sugar used in
SCM manufacture, although glucose and
other sugars have been used for diabetic
products. The sucrose is added in crystalline
form or as a solution by dissolving it in water
at about 95 ° C (203 ° F) before adding it to
milk by high shear recirculation in the milk.
The time of sugar addition infl uences product
quality. Adding sucrose before heat treatment
increases heat resistance of bacteria and their
enzymes, leading to age thickening, and
adding sucrose before evaporation causes
increased viscosity. Hence, the best time for
adding sucrose to give optimal product
quality is near the end of evaporation. The
fi nal concentration of sugar in the aqueous
phase of SCM, known as the sugar number
or sugar index, is approximately 62.5% to
64.5%.