Agriculture Reference
In-Depth Information
In recent years, emphasis has been placed on shorter
chilling cycles and lower temperatures - 'quick chilling' -
for the following reasons:
1
Both time and building space are saved, and higher
rates of product handling are achieved. Overheads in
labour are reduced and capital investment in buildings
is minimised.
2
The meat is said to have a better keeping quality because
lower air temperatures (usually below −3°C initially)
retard the rate of growth of bacteria on the surface of
carcases where their concentration is most pronounced.
3
Shrinkage of meat is reduced substantially - an impor-
tant economic factor.
4
The 'bloom' is said to be enhanced by quick chilling.
Legislation
Currently, legislation on refrigeration tends to concentrate on
the desired outcome of maintaining the cold chain in order to
minimise the growth of pathogens or spoilage micro-
organisms. This is key to the operators' responsibility to
maintain a food safety management system incorporating
'pre-requisites' and implementing the principles of HACCP.
Temperature controls are often considered to be part of a
HACCP pre-requisite programme. These requirements
encompass not only effective refrigeration equipment in
rooms handling, storing and transporting fresh meat but also
a requirement to ensure sufficient airflow and ventilation
to reduce humidity and facilities that are sufficiently large
to prevent overloading particularly during peak production
periods.
Regulation No. 853/2004 requires red meat to be reduced
from a muscle temperature of 35-40°C at slaughter to an
internal temperature of 7°C, white meat to 4°C and offal
to 3°C, progressively.
The legislation also requires the refrigeration system
to be itted with recording equipment which can monitor
and control the temperatures of the storage or working
environment so as to monitor and adjust the equipment
to achieve the desired effect. Automatic monitoring system
should be itted with an audible and visible alarm. Most
alarm systems now have the capability to be viewed remotely
through mobile communication devices.
Regular recalibration of monitoring equipment is essential.
In order to achieve the aforementioned objectives, dif-
ferent time/temperature schedules exist for the different
kinds of carcases. Surface discolouration and freezing of
the carcase must be avoided.
Prior to the second half of the twentieth century, it was
customary to hang beef carcases at ambient temperatures
for 24 hours before placing them in chill rooms. (Indeed, in
many abattoirs at that time, refrigeration was non-existent.)
Chilling times of 36-48 hours for lowering the deep round
temperature of beef carcases to 7°C are still common.
Quick chilling
refers to a rapid lowering of carcase
temperature starting not later than 1 hour after slaughter
and avoiding freezing.
Low temperatures and high air speeds incur a risk of
cold shortening. Pig carcases, however, should be cooled
as quickly as is economically feasible as they are less
susceptible to cold shortening.
The phenomenon of
cold shortening
was first encoun-
tered in New Zealand when rapid cooling schedules for
lamb freezing were first introduced. Toughness of the meat
occurred owing to extreme contraction of muscles sub-
jected to temperatures of around 10°C before the muscles
were in normal rigour, that is, while the pH was still above
6.2 and adenosine triphosphate (ATP) was still present.
Cold shortening can also occur with beef carcases and even
in parts of the carcase, for example, the loin, with fairly
slow chilling. It can be avoided by delaying the start of
chilling, for example, for 10-12 hours when the pH will be
below 6.2 and rigour will have taken place with the com-
plete disappearance of ATP from the muscle, or not chilling
to below 10°C in less than 10 hours. Cold shortening can
also be prevented by the use of electrical stimulation, which
advances the onset of rigour (see also Chapter 6).
Various schedules are in operation for the chilling of
meat, but many of these pay little attention to the time
required for heat to be extracted from the centre of heavy
muscle and dispersed at the surface. Important issues are
the velocity of air over the carcases, the uniform airflow
Ammonia
, first introduced in 1876, is still used
extensively today, although it is somewhat corrosive and
has a penetrating odour so that leaks can affect stored
products. There is a revival of interest in ammonia as a
refrigerant for larger plants because of the lesser effect on
the ozone layer. Today, the chlorofluorocarbons (CFCs) -
primarily the freons - are being replaced by hydrofluro-
carbons (HFC), again because of the lower ozone depletion
potential, this time due to the absence of chlorine.
The temperature utilised in refrigerating chambers
falls into two main categories according to whether the
meat is
chilled
or
frozen
, but whichever method is
employed, the important points are constant tempera-
ture, good air circulation and right humidity.
Chilling of meat
Chilling
scarcely affects the flavour, appearance or
nutritional value of meat and is particularly useful for
short-term preserving. The meat is maintained at about
+1°C and preferably in the dark, for light accelerates the
oxidation of fat with the liberation of free fatty acids and
the production of rancidity. The atmosphere is kept dry
to hinder the formation of moulds, which are more likely
to attack chilled meat than frozen.
