Unformatted text preview: he outer layer of the product and
seals in the juices, aromatics, and flavoring agents. The product quality is
also affected adversely by temperature fluctuations of the storage room.
The ordinary refrigeration of foods involves cooling only without any
phase change. The freezing of foods, on the other hand, involves three
stages: cooling to the freezing point (removing the sensible heat), freezing
(removing the latent heat), and further cooling to the desired subfreezing
temperature (removing the sensible heat of frozen food), as shown in Figure 4–36. Beef Products
Meat carcasses in slaughterhouses should be cooled as fast as possible to a
uniform temperature of about 1.7°C to reduce the growth rate of microorganisms that may be present on carcass surfaces, and thus minimize
spoilage. The right level of temperature, humidity, and air motion should
be selected to prevent excessive shrinkage, toughening, and discoloration.
The deep body temperature of an animal is about 39°C, but this temperature tends to rise a couple of degrees in the midsections after slaughter as
a result of the heat generated during the biological reactions that occur in
the cells. The temperature of the exposed surfaces, on the other hand, tends
to drop as a result of heat losses. The thickest part of the carcass is the
round, and the center of the round is the last place to cool during chilling.
Therefore, the cooling of the carcass can best be monitored by inserting a
thermometer deep into the central part of the round.
About 70 percent of the beef carcass is water, and the carcass is cooled
mostly by evaporative cooling as a result of moisture migration toward the
surface where evaporation occurs. But this shrinking translates into a loss
of salable mass that can amount to 2 percent of the total mass during an
overnight chilling. To prevent excessive loss of mass, carcasses are usually
washed or sprayed with water prior to cooling. With adequate care, spray
chilling can eliminate carcass cooling shrinkage almost entirely.
The average total mass of dressed beef, which is normally split into two
sides, is about 300 kg, and the average specific heat of the carcass is about
3.14 kJ/kg · °C (Table 4–5). The chilling room must have a capacity equal
to the daily kill of the slaughterhouse, which may be several hundred.
A beef carcass is washed before it enters the chilling room and absorbs a
large amount of water (about 3.6 kg) at its surface during the washing
process. This does not represent a net mass gain, however, since it is lost by
dripping or evaporation in the chilling room during cooling. Ideally, the
carcass does not lose or gain any net weight as it is cooled in the chilling
room. However, it does lose about 0.5 percent of the total mass in the holding room as it continues to cool. The actual product loss is determined by
first weighing the dry carcass before washing and then weighing it again
after it is cooled.
The refrigerated air temperature in the chilling room of beef carcasses
must be sufficiently high to avoid freezing and discoloration on the outer cen58933_ch04.qxd 9/10/2002 9:13 AM Page 243 243
Maximum carcass temp (deep round)
Temperature, °C 30
Avg. carcass temp (all parts)
20 Minimum carcass temp (chuck surface) 10
Room air temp.
–10 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72
Time from start of chill, hours surfaces of the carcass. This means a long residence time for the massive
beef carcasses in the chilling room to cool to the desired temperature. Beef
carcasses are only partially cooled at the end of an overnight stay in the
chilling room. The temperature of a beef carcass drops to 1.7 to 7°C at the
surface and to about 15°C in mid parts of the round in 10 h. It takes another
day or two in the holding room maintained at 1 to 2°C to complete chilling
and temperature equalization. But hog carcasses are fully chilled during
that period because of their smaller size. The air circulation in the holding
room is kept at minimum levels to avoid excessive moisture loss and discoloration. The refrigeration load of the holding room is much smaller than
that of the chilling room, and thus it requires a smaller refrigeration system.
Beef carcasses intended for distant markets are shipped the day after
slaughter in refrigerated trucks, where the rest of the cooling is done. This
practice makes it possible to deliver fresh meat long distances in a timely
The variation in temperature of the beef carcass during cooling is given
in Figure 4–37. Initially, the cooling process is dominated by sensible heat
transfer. Note that the average temperature of the carcass is reduced by
about 28°C (from 36 to 8°C) in 20 h. The cooling rate of the carcass could
be increased by lowering the refrigerated air temperature and increasing
the air velocity, but such measures also increase the risk of surface freezing.
Most meats are judged on their tenderness, and the preservation of tenderness is an important consideration in the refrigeration and freezing of
meats. Meat consists prima...
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