Dairy Ingredients for Food Processing

130 Chapter 5

(98.6 ° F) and above, and may cause acid

coagulation and a slight cheesy odor. B. sub-

tilis causes non - acid curd with a bitter taste.

Clostridium sp. causes the putrefaction and

gas production with a odor of H 2 S.

Manufacture of Sweetened

Condensed Milk

Sweetened condensed milk is manufactured

from whole milk, skim milk or recombined

condensed milk (consisting of skim milk

powder, anhydrous milk fat or vegetable fat,

and water). The processing steps in the man-

ufacture of SCM are as follows:

1. Standardization of milk


2. Heat treatment of milk


3. Evaporation


4. Addition of sugar


5. Cooling


6. Seeding and subsequent cooling for
   crystallization


7. Canning and packaging
   Raw milk of good microbiological quality
   and low spore counts is the preferred starting
   material. When nonfat dry milk (or skim milk
   powder) is used for recombined SCM, it must
   also have a good microbial quality and low
   spore counts.

Standardization

The raw milk is standardized to 8% fat and

21% SNF, giving a fat:SNF ratio of 0.381.

Standardization is achieved using any of the

ingredients described in the CODEX stan-

dard or in the respective country. Following

standardization, the milk is given an initial

heat treatment (80 ° C to 120 ° C; 176 ° F to

284 ° F) similar to that used for evaporated

milk manufacture. The heat treatment infl u-

ences viscosity of the fi nal product and age

thickening during storage. Heat treatment in

the range of 90 ° C to 100 ° C (194 ° F to 212 ° F)

gives the product its greatest susceptibility to

plasmin and other bacterial enzymes that
may be present in the milk. The adequacy of
sterilization is checked by holding random
samples of the cooled canned evaporated
milk for two to three weeks at 27 ° C to
30 ° C (80 ° F to 86 ° F) and checking for spoil-
age (i.e., microbial growth, gas formation,
bulg ing and explosion of cans) before ship-
ping. When product is to be shipped to
warmer climates, incubation of the cans may
be done at 37 ° C (96.8 ° F) or 55 ° C (131 ° F) to
detect facultative or obligate thermophilic
bacteria, respectively.
Evaporated milk must be commercially
sterilized to have an acceptable shelf life at
room temperature, which means that it must
not contain organisms that will grow under
normal storage conditions. Although obliga-
tory thermophilic organisms may grow at
high temperatures such as 45 ° C (113 ° F), the
product is still considered commercially
sterile. A time - temperature combination to
give absolute sterility is possible; however,
the resultant product has an unacceptable
cooked fl avor and a dark color resulting from
Maillard browning.
Sterilization may also be done by ultra -
high - temperature (UHT) heating at 130 ° C to
140 ° C (266 ° F to 284 ° F) using direct or indi-
rect heating. After sterilization, the cans are
sealed aseptically. Aseptic packaging occurs
under pressure at temperatures exceeding
100 ° C.

Spoilage of Evaporated Milk

Sterilization is designed to kill heat - resistant
spores, most of which in milk are species of
the genus Bacillus or occasionally
Clostridium. However, inadequate cooling
and/or storage at high temperatures may
cause growth of some heat - resistant spores.
The most heat - resistant spore in milk is
Bacillus stearothermophilus. This organism
may not grow in temperate climates but
grows well under tropical conditions. Bacillus
stearothermophilus grows best at 37 ° C