Preservation of meat - Gracey's Meat Hygiene - page 74

provision of temperature indicators in the driving cab
and properly spaced overhead rails. In addition, it should
be economical, lightweight and noiseless.
The maintenance of the internal temperature is influ-
enced by the difference between the inside and outside
temperatures, insulation, the number of times the doors
are opened and closed, loading temperature of the cargo,
capacity rating of the refrigeration system, respiration
rate of the product, etc. Vehicles left standing with doors
wide open in high summer temperatures attract not only
heat but also undesirable arthropods.
An efficient insulating medium is provided by ure-
thane foam sprayed between inner and outer linings.
This material expands to fill all crevices and has a low
heat loss factor, a low water absorption rating and a den-
sity of 23-38 kg/cubic metre. Lining materials must be
smooth, impermeable, durable, easily cleaned and able
to withstand detergents and hot water. They must also be
non-toxic and as far as possible free from seams. Typical
lining materials are glass fibre-reinforced panels, special
non-marking aluminium (bare aluminium can mark
fresh unwrapped hanging meat) and plastic-coated and
stainless steel sheeting.
Floors should be very durable, watertight and easily
cleaned. There should be no crevices or sharp corners
throughout the inside of the vehicle which would hinder
cleaning.
While construction of transport vehicles is normally
suitable for hanging quarters of beef, lamb carcases, pack-
aged meat, etc., the same does not hold for offal which is
not in cartons. It is important that for the retail delivery of
meat and offal, there should be good handling facilities; it
must not be placed in an unwrapped state on the floor.
Loading should be effected into a previously chilled vehi-
cle which has its own refrigeration unit and is well insu-
lated, should be direct from the cold store into the vehicle
and, whenever possible, should be made using an
enclosed loading bay. This prevents temperature increase
during the loading operation. The vehicle temperature
during transit should be monitored and recorded.
When the vehicle is unloaded, either into a transit
cold store or at its final delivery point, product tempera-
ture should be checked before unloading, and transfer to
the chilled storage should be immediate.

become insoluble and do not regain their solubility
when the meat is thawed. A similar irreversible change
may be observed if eggs are frozen.
2 The freezing point of meat lies between −1 and −1.5°C,
when crystals begin to form: at −1.5°C, 35.5% of the
muscle water is ice; at −5°C, 82% is ice; and at −10°C,
94% is ice. During freezing, the water present in the
muscle fibres diffuses from the muscle plasm to form
crystals of ice. In the past, it has been believed that the
speed of freezing has an important bearing on the size
of the ice crystals and the future quality of the product.
It has previously been postulated that when meat is
frozen slowly , the largest crystals are formed between
the temperatures of −0.5 and −4°C and are largely
located outside the muscle fibres; this temperature
range is known as the zone of maximum ice formation ,
and where meat is subsequently stored within this
range, the ice crystals continue to grow in size during
storage. It has also been surmised that if meat is frozen
rapidly to a temperature lower than −4°C, the ice crys-
tals are small and lie mainly within the muscle fibres; if
lowering of the temperature is sufficiently fast, many of
the crystals are ultramicroscopic in size, and all of
them are smaller than the cells in which they are
formed. Doubt is now being cast on this theory as the
rate of freezing appears to have minimal effect on thaw-
ing drip loss. Quick freezing of meat has made rapid
strides and is applied to lambs, calves, pigs, poultry,
fish and various wholesale cuts, the latter being distrib-
uted wrapped in cellophane or a latex rubber container
base. The temperature of a food may be reduced by
quick freezing to as low as −46°C by contact with metal
against which streams of brine at very low tempera-
tures are directed; some methods use atomised sprays
of cold brine, which produce no distortion of the mus-
cle cells and practically no 'drip' on thawing. It is, how-
ever, unlikely that the quick freezing of whole quarters
of beef will become a commercial proposition, for a
temperature of −275°C would be required to quick-
freeze a quarter of beef in 30 minutes.

'Weeping' or 'drip'
Weeping denotes the presence of a watery, bloodstained
fluid which escapes from frozen meat when it is thawed
and consists mainly of water, together with salts, protein
and damaged blood corpuscles. The latter are responsi-
ble for the pink colouration of the fluid and are readily
recognisable on microscopical examination. Weeping
is an undesirable feature and is caused partly by the
rupture of the muscle cells and tissues by crystals of ice
and partly by irreversible changes in the muscle plasm.
The amount of drip is greater in beef than in mutton,

Changes in frozen meat
Two outstanding and unfavourable changes take place as
a result of the freezing of meat:

1 The physical state of the muscle plasm (globulin and
albumen proteins) is considerably altered. When meat
is frozen below −2°C, the formation of ice crystals so
raises the concentration of these proteins that they