Some Class Results

No. of ribs in roast

Weight

Searing temper-ature °C.

Cooking temper-ature °C.

Interior temper-ature when removed from oven

Cooking time

Total cooking losses, per cent

grams

pounds

Total, min-utes

Time per pound

One

836

1.8

275

125

55

59

33.0

8.4

Two

1560

3.4

275

125

55

93

38 2

11.8

Two

2331

5.1

275

125

55

100

19.5

10.9

Two

2813

6.2

275

125

56

124

20.0

15.1

One

835

1.8

275

125

65

81

45.0

11.0

Two

1575

3.3

275

125

65

116

33.3

14.9

Two

1626

3.6

275

125

65

140

36.0

14.8

Two

1890

4.2

275

125

65

110

26.3

14.0

One

757

1.7

275

125

75

85

50.0

20.0

Two

1603

3.5

275

125

75

190

53.3

21.4

Two

1758

3.9

275

125

75

127

32.5

25.0

Two

2268

5.0

275

125

75

260

52.0

20.2

Surface area. Since time per pound does not give a dependable basis for cooking meat an effort is often made to express cooking time in relation to the surface area. Often this is expressed in the following way. The greater the surface area the shorter the time required for cooking a piece of meat if all other conditions are standardized. From the diagrams, Fig. 25, it can be seen that this method would give a less variable cooking time, at least for some pieces of meat of certain shape, than time per pound. This method of expressing time for cooking is also more difficult to determine in the home.

Stage to which the meat is cooked. Cooking meat rare does not require so long a time as cooking medium well done or well done, because the last two stages require a higher inner temperature. See Table 29.

The composition of the meat. The proportion of fat and lean in the meat affects the time required for cooking. There has been much confusion regarding the rate of heat conduction by fat. In physiology, one is told that a layer of fat over the muscles prevents loss of body heat, because the fat is a poor conductor of heat. In articles on cooking various foods, one often sees the statement that fat conducts heat more readily than muscle tissue. These two seemingly contradictory statements are explainable. Redfield has offered a solution. In studying the rate of heat penetration in canning pork and beef, she found, with all other conditions standardized, that the temperature at the center of the can of pork rose more slowly than the temperature at the center of the can of beef. In order to determine whether this slower heat conduction in the pork was due to its greater fat content, she packed some cans with suet and others with beef round free of all visible fat. She found that the temperature of the suet rose more slowly than that of the beef round until the melting point of the suet was reached. As soon as the fat melted, it conducted the heat faster than the beef round. Fat in a liquid form in cooking is a good conductor of heat, but if it is in a solid form it is a poor conductor of heat. In Redfleld's experiments, the fat escaped from the fat cells, the connective tissue forming a piece about the size of a marble around the point of the thermocouple.

The writer's experimental classes, in processing suet, fat pork, lean beef, and lean pork in pint cans in a hot water bath, have found the rate of heat penetration to be much slower in the fat meat than in the lean, even at temperatures of 90°C. and above. When the suet was packed tightly into the jar so that the tissues surrounding the fat cells were broken, Redfield's results were checked.

Degree of ripeness. Alexander and Clark found that increasing the length of the ripening period after slaughter shortened the time required to roast leg of lamb. As the ripening period increased beyond two days after slaughter, the cooking shrinkage became smaller and the rate of heat penetration more rapid.

Thus it seems that, if the connective tissue remains unbroken, as it does in the more solid fat and the interior fat of meat cuts, it prevents the fat globules from touching each other and delays heat penetration.

Rise of Interior Temperature of Meat after the Cooking Process Has Been Stopped

When a roast is removed from the oven or a piece of cooked meat is removed from the cooking utensil the temperature in the interior may continue to rise. Heat is carried to the interior of the meat by conduction, that is, from fiber to fiber. When the cooking process is stopped the temperature of the meat half way to the center is higher than the temperature at the center. This heat is conducted both toward the center and the outer edge of the meat, and as a consequence the temperature at the center of the meat rises.

The factors that may determine the extent of this rise in temperature after removal from the oven are: (1) the cooking temperature; (2) the inner temperature of the meat when the cooking process is stopped; (3) the size of the piece of meat; (4) the composition. It must be remembered that each of these factors may have an influence on the temperature rise of the same piece of meat, and that under some conditions one factor may influence it more than another. Thus they cannot be considered separately, for the high cooking temperature of a steak or roast may affect the temperature rise more than the size. Yet under some conditions size is a greater factor in determining temperature rise.

Cooking temperature and temperature rise after the cooking process is stopped. The higher the cooking temperature the greater the tendency for a rise in the inner temperature of the meat. A higher cooking temperature produces a higher surface temperature, and consequently results in a higher rise at the interior after the cooking process is stopped.

Inner temperature. The lower the inner temperature at which the cooking is stopped, the greater the tendency for the rise of inner temperature. This is because with a low inner temperature there is a wider variation between the inner and surface heat, which results in greater rise of inner temperature. The inner temperature of foods that contain a high percentage of water, such as cake, meat, and potatoes, never rises above the boiling point of their juices. Heat supplied in amounts greater than the amount needed to reach the boiling point of the juices is used in evaporating the liquid. It is impossible to raise the inner temperature of meat above 100°C. without having a very dry, charred product.

Size. In larger pieces of meat, the size of the piece is not so important a factor as those mentioned above in affecting the temperature rise of the interior after cooking has been stopped. But a piece of meat may be so small or thin that the inner temperature does not rise after the cooking process is stopped, because of the rapid cooling from the surface.

Composition and duration of temperature rise. No definite relation has been established between composition of the meat and the extent of the inner temperature rise after cooking. It does seem to affect the duration of the temperature rise more than the extent. Meat containing a great deal of fat and meat that has a very thick layer of fat on the surface, 3/4 to 1 inch or more, requires a long time for the inner temperature to reach its maximum point. A roast with such a layer of fat may take as long as 1 to 1 1/2 hours to reach its maximum inner temperature, whereas a lean roast of the same shape, and cooked under the same conditions, may take only 12 to 30 minutes to reach its maximum interior temperature, after the cooking process is stopped.