Preservation of meat - Gracey's Meat Hygiene - page 72

In high-throughput establishments, the most efficient
protocol is to chill carcases initially in a 'pre-chiller'
using a high rate of heat exchange to remove much of the
heat at the surface rapidly, before transfer of the carcases
to the main chillers with a lower rate of heat exchange.

Table 4.3 Practical Storage Life (PSL) at different storage
temperatures

PSL (months)

−12°C −18°C −24°C

Freezing of meat
The chief types of meat foods preserved by freezing , as
distinct from chilling, are mutton, lamb, pork and rabbit,
but there are rather wide differences of opinion as to the
proper freezing temperature. In Germany, the tempera-
ture is maintained at −6°C and in Australia −11°C. In
South America, much lower temperatures may be used
in what are termed sharp freezers ; for example, pork
may be stored at −18°C, which prevents oxidation and
resultant rancidity. During sea transport, a temperature
of −9 to −8°C is maintained in the holds, while the air is
kept dry and in circulation.
In the United Kingdom, it has been customary to hold
meat in cold stores at temperatures of −20°C. It is now
generally recognised that lower temperatures are more
satisfactory since they reduce deterioration of carcase
meat, and temperatures no higher than −18°C, even −30°C,
are now being advocated. It was believed that very low
temperatures resulted in excessive dehydration; this is now
considered to be incorrect.
Current EU legislation does not specify temperatures
at which meat should be stored but rather simply states
that it should be frozen without delay and that time
should be allowed to allow the temperature of the meat
to stabilise. Previous legislation stated that this stabilisa-
tion should permit beef quarters should be accepted for
freezing at a temperature not above +7°C and frozen
within 36 hours to an internal temperature of −7°C or
below. The acceptance temperature of pig sides is below
+4°C; they must be frozen at −30°C and held in the
freezer until all the meat is at −15°C or below. Frozen
storage for beef must be at a temperature of −17°C and at
−20°C for pig meat.
Such low temperatures can be attained only in special
blast freezers with air temperatures of around −34°C, air
speeds of about 3-5 m/s and holding times of up to 25
hours. The form of wrapping greatly affects the freezing
time; if it is loose, the pockets of air or cartons act as
insulation and thereby increase freezing times. Wrapping
in moisture-proof packaging, or traditionally in stocki-
nette, can offset water loss.
Cold stores are designed to hold frozen meat and
other foods at a required temperature, although various
temperatures and air speeds are used in different prem-
ises. While the meat trade in Britain is resistant to the
use of very low temperatures for cold storage, work at
the UK Meat Research Institute at Bristol has shown that
at −10°C weight losses of meat are much greater than

Beef carcases 8 15 24

Lamb carcases 18 24 >24

Pork carcases 6 10 15

Edible offals 4 1-2 18

Source: Refrigeration and Process Engineering Research Centre,
University of Bristol, Churchill Building, Langford, Bristol, UK.

at −30°C because the amount of water vapour that air
can hold before it becomes saturated increases as
temperature rises.
The commonly held belief that frozen meat will keep
indefinitely is not true. The practical storage life (PSL) of
frozen carcase meat is given in Table 4.3.
For optimum results in chilling and freezing and the
prevention of growth of spoilage and food-poisoning
bacteria, the following criteria should be adopted:
1 Initial design of refrigeration space must consider
product tenderness, weight loss, possibility of spoilage,
size of individual units, space required, rail height and
floor and wall surfaces.
2 Temperatures must be checked regularly.
3 Overloading must be avoided and carcases must not
touch each other.
4 Door opening and closing must be kept to a
minimum.
5 Adequate airflow around carcases is essential.
6 Carcases of different species must not occupy the
same area.
7 Cold shortening must be avoided by not chilling below
10°C in less than 10 hours.

Liquid nitrogen
This refrigerant is increasingly being used in the
food industry, especially for freezing and automated
production lines. A moving belt carries the food through
a tunnel and under a liquid nitrogen spray at the outlet.
The food is frozen and the vaporised nitrogen is extracted
by fans and discharged to the atmosphere. The liquid
nitrogen is stored in vacuum-insulated tanks.
This form of cryogenic freezing is said to produce less
dehydration (usually <0.3%) and better flavour, colour,
aroma, texture and nutritive value in the food than the
conventional types which utilise large volumes of cold
air on the product. Higher operating efficiency and low
running and maintenance costs are also claimed. Being
constructed in stainless steel and capable of being