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Unformatted text preview: and in less than 8 h for
carcasses more than 3.6 kg. Meeting these requirements today is not difficult since the slow air chilling is largely replaced by the rapid immersion
chilling in tanks of slush ice. Immersion chilling has the added benefit that
it not only prevents dehydration, but it causes a net absorption of water and
thus increases the mass of salable product. Cool air chilling of unpacked
poultry can cause a moisture loss of 1 to 2 percent, while water immersion
chilling can cause a moisture absorption of 4 to 15 percent (Fig. 4–42).
Water spray chilling can cause a moisture absorption of up to 4 percent.
Most water absorbed is held between the flesh and the skin and the
connective tissues in the skin. In immersion chilling, some soluble solids
are lost from the carcass to the water, but the loss has no significant effect
Many slush ice tank chillers today are replaced by continuous flow-type
immersion slush ice chillers. Continuous slush ice-chillers can reduce the
internal temperature of poultry from 32 to 4°C in about 30 minutes at a rate
up to 10, 000 birds per hour. Ice requirements depend on the inlet and exit
temperatures of the carcass and the water, but 0.25 kg of ice per kg of carcass is usually adequate. However, bacterial contamination such as salmonella remains a concern with this method, and it may be necessary to
chloride the water to control contamination.
Tenderness is an important consideration for poultry products just as it is
for red meat, and preserving tenderness is an important consideration in the
cooling and freezing of poultry. Birds cooked or frozen before passing
through rigor mortis remain very tough. Natural tenderization begins soon
after slaughter and is completed within 24 h when birds are held at 4°C.
Tenderization is rapid during the first three hours and slows down thereafter. Immersion in hot water and cutting into the muscle adversely affect
tenderization. Increasing the scalding temperature or the scalding time has
been observed to increase toughness, and decreasing the scalding time has
been observed to increase tenderness. The beating action of mechanical
feather-picking machines causes considerable toughening. Therefore, it is
recommended that any cutting be done after tenderization. Cutting up the
bird into pieces before natural tenderization is completed reduces tenderness considerably. Therefore, it is recommended that any cutting be done
after tenderization. Rapid chilling of poultry can also have a toughening cen58933_ch04.qxd 9/10/2002 9:13 AM Page 247 247
Storage life (days) 12
–2 0 5 10 15
Storage temperature, °C FIGURE 4–43
The storage life of fresh poultry
decreases exponentially with
increasing storage temperature. 9
Freezing time, hours effect. It is found that the tenderization process can be speeded up considerably by a patented electrical stunning process.
Poultry products are highly perishable, and thus they should be kept at
the lowest possible temperature to maximize their shelf life. Studies have
shown that the populations of certain bacteria double every 36 h at 2°C,
14 h at 0°C, 7 h at 5°C, and less than 1 h at 25°C (Fig. 4–43). Studies have
also shown that the total bacterial counts on birds held at 2°C for 14 days
are equivalent to those held at 10°C for 5 days or 24°C for 1 day. It has also
been found that birds held at 1°C had 8 days of additional shelf life over
those held at 4°C.
The growth of microorganisms on the surfaces of the poultry causes the
development of an off-odor and bacterial slime. The higher the initial
amount of bacterial contamination, the faster the sliming occurs. Therefore,
good sanitation practices during processing such as cleaning the equipment
frequently and washing the carcasses are as important as the storage temperature in extending shelf life.
Poultry must be frozen rapidly to ensure a light, pleasing appearance.
Poultry that is frozen slowly appears dark and develops large ice crystals
that damage the tissue. The ice crystals formed during rapid freezing are
small. Delaying freezing of poultry causes the ice crystals to become larger.
Rapid freezing can be accomplished by forced air at temperatures of 23
to 40°C and velocities of 1.5 to 5 m/s in air-blast tunnel freezers. Most
poultry is frozen this way. Also, the packaged birds freeze much faster on
open shelves than they do in boxes. If poultry packages must be frozen in
boxes, then it is very desirable to leave the boxes open or to cut holes on
the boxes in the direction of airflow during freezing. For best results, the
blast tunnel should be fully loaded across its cross-section with even spacing between the products to assure uniform airflow around all sides of the
packages. The freezing time of poultry as a function of refrigerated air temperature is given in Figure 4–44. Thermal properties of poultry are given in
Other freezing methods for poultry include sandwiching between cold
plates, immersion into a refrigerated liquid such as glycol or calcium chloride brine, and cryogenic cooling with liquid nitrogen. Poultry can be
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This note was uploaded on 01/28/2010 for the course HEAT ENG taught by Professor Ghaz during the Spring '10 term at University of Guelph.
- Spring '10