Freezing/Thawing 121or quarters, or boned out in cartons. Freezing
times in such systems are typically 25 to 72
hours. Some offal is frozen in plate freezers.
Small processed items are typically frozen in
continuous belt freezers or in cryogenic
tunnels.
Crust freezing and tempering are increas-
ingly being used to allow high - speed mechan-
ical portioning or slicing of meat and meat
products. The fi nal temperature distribution
produced by the freezing system is critical in
such operations.
Although a great deal has been written on
the frozen storage life of different meats, the
underlying data are backed up by a relatively
small number of controlled scientifi c experi-
ments. Much of the scientifi c data date back
to the time when meat was either stored
unwrapped or in wrapping materials that are
no longer used. It is not surprising when we
consider the changes in packaging and han-
dling methods over the last century that there
is a considerable scatter in data on storage
lives for similar products.
In recent years, energy conservation
requirements have caused an increased inter-
est in the possibility of using more effi cient
storage temperatures than have been used to
date. Researchers, such as Jul, have ques-
tioned the wisdom of storage below − 20 ° C
and have asked whether there is any real eco-
nomic advantage in very low temperature
preservation. There is a growing realization
that storage lives of several foods can be less
dependent on temperature than previously
thought. Since research has shown that red
meats often produce nonlinear time - temper-
ature curves, there is probably an optimum
storage temperature for a particular product.
Improved packing and preservation of prod-
ucts can also increase storage life and may
allow higher storage temperatures to be used.
One suggestion is that with storage at − 18 ° C,
low - stability meats such as mechanically
recovered meat should be stored for 8 months
or less, medium - stability meats such as pork
and processed meats should be stored forchilled product so that it is suitable for
mechanical processing. Crust freezing is
often used for the same purpose but is essen-
tially a less controlled process where only the
surface is frozen. In tempering, product is
semifrozen so that it is stiff enough to be
sliced, cubed, etc. without deformation.
Reducing deformation during cutting im -
proves the yield, by enabling faster cutting
and reducing the number of misshapen slices.
However, the process must be carefully con-
trolled. The optimum tempering temperature
is a function of the meat and the slicer. If too
much of the water in the meat is frozen, the
subsequent sliced, diced, or chopped meat is
likely to show a large increase in the amount
of drip released. Also, when the temperature
is too low, the hard meat may shatter, and
blade wear is excessive. When the tempera-
ture is too high, the soft meat will deform and
may stick to the blade, and the fat may be
torn away from the lean.
Methods for tempering or crust freezing
are essentially the same as those used for
freezing. A small number of operations use
plate freezer, liquid immersion systems, and
cryogenic tunnels to temper bacon for high -
speed slicing. However, the majority of
industrial systems employ air in a single or
two - stage process. Since the temperature of
a fully tempered product is critical, it can
take a long time to be achieved in a single
stage process.
Conclusions
Under commercial conditions, differences in
freezing rates are unlikely to produce notice-
able changes in the organoleptic quality of
the meat produced. However, current legisla-
tion requires a minimum meat temperature of
− 12 ° C to be achieved before meat is moved
from the freezing system. Freezing time
is therefore of considerable economic
importance.
Most unprocessed meat is either frozen in
batch air systems as bone - in carcasses, sides,