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Unformatted text preview: rily of bundles of tiny muscle fibers bundled together inside long strings of connective tissues that hold it together. The
tenderness of a certain cut of beef depends on the location of the cut, the
age, and the activity level of the animal. Cuts from the relatively inactive
mid-backbone section of the animal such as short loins, sirloin, and prime
ribs are more tender than the cuts from the active parts such as the legs and
the neck (Fig. 4–38). The more active the animal, the more the connective
tissue, and the tougher the meat. The meat of an older animal is more flavorful, however, and is preferred for stewing since the toughness of the
meat does not pose a problem for moist-heat cooking such as boiling. The FIGURE 4–37
Typical cooling curve of a beef carcass
in the chilling and holding rooms at an
average temperature of 0°C (from
ASHRAE, Handbook: Refrigeration,
Ref. 3, Chap. 11, Fig. 2). Chuck Rib Short
Foreshank Short plate Sirloin Round FIGURE 4–38
Various cuts of beef (from National
Livestock and Meat Board). cen58933_ch04.qxd 9/10/2002 9:13 AM Page 244 244
Tenderness scale 10 5 0 5
Time in days 10 FIGURE 4–39
Variation of tenderness of meat stored
at 2°C with time after slaughter. Meat freezer
– 40 to –30°C
2.5 to 5 m/s
Meat FIGURE 4–40
The freezing time of meat can be
reduced considerably by using low
temperature air at high velocity. TABLE 4–6
Storage life of frozen meat products
at different storage temperatures
(from ASHRAE Handbook:
Refrigeration, Chap. 10, Table 7)
Storage Life, Months
Cooked foods 12°C
2–3 18°C 23°C 6–18 12–24
2–4 protein collagen, which is the main component of the connective tissue,
softens and dissolves in hot and moist environments and gradually transforms into gelatin, and tenderizes the meat.
The old saying “one should either cook an animal immediately after
slaughter or wait at least two days” has a lot of truth in it. The biomechanical reactions in the muscle continue after the slaughter until the energy
supplied to the muscle to do work diminishes. The muscle then stiffens and
goes into rigor mortis. This process begins several hours after the animal is
slaughtered and continues for 12 to 36 h until an enzymatic action sets in
and tenderizes the connective tissue, as shown in Figure 4–39. It takes
about seven days to complete tenderization naturally in storage facilities
maintained at 2°C. Electrical stimulation also causes the meat to be tender.
To avoid toughness, fresh meat should not be frozen before rigor mortis has
You have probably noticed that steaks are tender and rather tasty when
they are hot but toughen as they cool. This is because the gelatin that
formed during cooking thickens as it cools, and meat loses its tenderness.
So it is no surprise that first-class restaurants serve their steak on hot thick
plates that keep the steaks warm for a long time. Also, cooking softens the
connective tissue but toughens the tender muscle fibers. Therefore, barbecuing on low heat for a long time results in a tough steak.
Variety meats intended for long-term storage must be frozen rapidly to
reduce spoilage and preserve quality. Perhaps the first thought that comes
to mind to freeze meat is to place the meat packages into the freezer and
wait. But the freezing time is too long in this case, especially for large
boxes. For example, the core temperature of a 4–cm-deep box containing
32 kg of variety meat can be as high as 16°C 24 h after it is placed into a
30°C freezer. The freezing time of large boxes can be shortened considerably by adding some dry ice into it.
A more effective method of freezing, called quick chilling, involves the
use of lower air temperatures, 40 to 30°C, with higher velocities of
2.5 m/s to 5 m/s over the product (Fig. 4–40). The internal temperature
should be lowered to 4°C for products to be transferred to a storage
freezer and to 18°C for products to be shipped immediately. The rate of
freezing depends on the package material and its insulating properties, the
thickness of the largest box, the type of meat, and the capacity of the refrigeration system. Note that the air temperature will rise excessively during initial stages of freezing and increase the freezing time if the capacity
of the system is inadequate. A smaller refrigeration system will be adequate
if dry ice is to be used in packages. Shrinkage during freezing varies from
about 0.5 to 1 percent.
Although the average freezing point of lean meat can be taken to be
2°C with a latent heat of 249 kJ/kg, it should be remembered that freezing occurs over a temperature range, with most freezing occurring between
1 and 4°C. Therefore, cooling the meat through this temperature range
and removing the latent heat takes the most time during freezing.
Meat can be kept at an internal temperature of 2 to 1°C for local use
and storage for...
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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