88 Chapter 3
Condensing is usually in the range of 2.5 : 1
to 4 : 1 depending on its intended use. Initially
the raw milk is homogenized and standard-
ized prior to condensing. The treated milk is
preheated, usually to 65.6 ° C to 76.7 ° C,
which can be raised to 82.2 ° C to 93.3 ° C to
impart different characteristics for particular
product applications. The milk is then con-
centrated in a vacuum pan or multiple effect
evaporator, usually at temperatures in the
range 54.4 ° C to 57.2 ° C. No sterilization
process is involved at any stage; therefore,
the fi nal product is not sterile and although
the a w is reduced, it is not suffi cient to com-
pletely inhibit microbial growth. Thus, the
product must be refrigerated as quickly as
possible and refrigeration maintained during
transport to its destination. In general, the
process has less lethality than pasteurization
and hence the product must not be labeled as
pasteurized.
As with evaporated milk, thermophilic
bacteria may build up during the condensing
stage if the process runs are protracted and
the hygiene questionable. However, unlike
evaporated milk, there is no subsequent ster-
ilization treatment. In general, the nature of
condensed milk emphasizes the need for
refrigeration and its rapid incorporation as an
ingredient into other more microbiologically
stable products. If spoilage occurs it is usually
attributed to psychrotrophic bacteria, yeasts,
or molds, and is the result of holding the
product for protracted periods under improper
storage conditions.
Sweetened condensed full - fat milk (SCM)
is regulated by the Codex Alimentarius and
requires a minimum of 8% milk fat and 28%
total milk solids. The product is used for
cooking, confectionery including chocolate
bars, to enrich tea or coffee, and after dilu-
tion, even as a milk drink. The process
usually involves forewarming (82 ° C to
100 ° C for 10 to 30 minutes), superheating,
sugar addition, condensing in a vacuum pan
at 57.2 ° C, cooling, forced crystallization, and
fi nally packaging. Forced crystallization con-performed at temperatures below 54.5 ° C
using a multistage falling fi lm evaporator;
hence the growth of thermophilic bacteria,
particularly as biofi lms, can occur if the
process runs are long and/or cleaning is not
adequate. Concentration can be performed
using reverse osmosis but this is rare. The
concentrate is homogenized and either steril-
ized and packed aseptically, usually in a can,
or subjected to in - container sterilization
using temperatures of 115 ° C for 15 to 20
minutes.
This process should kill all vegetative
organisms and spores, although spoilage
problems have arisen due to B. stearother-
mophilus, B. licheniformis, B. coagulans, B.
marcerans, and B. subtilis. If the integrity of
the can remains intact and the process has
been performed properly, then spoilage is
most likely to be the result of the action of
heat - stable extracellular enzymes derived
from psychrotrophic bacteria growing in the
original raw milk.
Concentrated milk, when destined for
human consumption as fl uid milk, is nor-
mally diluted appropriately before use. The
raw milk is fi rst pasteurized and then concen-
trated using the mildest heat treatment pos-
sible to minimize undesirable organoleptic
changes, then standardized and homogenized
before a fi nal pasteurization at an elevated
temperature (approximately 79.4 ° C for 25
seconds) to take account of the slower heat
transfer kinetics of the more viscous product.
Although the a w of the product is lower than
normal milk, it is not suffi cient to inhibit the
normal microfl ora and hence the pattern of
spoilage is essentially the same as for pas-
teurized milk.
Afl atoxin M1 can present a food safety
problem when cattle consume moldy grain
harboring afl atoxin B1 and it is converted
and excreted in the milk by the affected
animal.
Condensed milk is used as a source of
milk solids for confectionery, bakery prod-
ucts, ice cream, and other processed foods.