Storage of meat in the home. Proper storage of meat in the home is often a problem. Halves and quarters of dressed animals have a natural protective skin covering. But when wholesale cuts are divided into smaller parts, the surface area for contamination and the contamination both increase from these cut surfaces coming in contact with meat blocks, hands, wrapping paper, and kitchen and refrigerator utensils. In general, unless frozen, meat should not be stored long in the home. Low temperatures and dry circulating air increase the storage life of meat. Burnett found roasts keep best, steaks and chops next, and ground meat most poorly.

Rigor. During rigor meat is less tender than after the passage of rigor, so that rigor is of interest in meat cookery.

Cause. The exact cause for the development of rigor is not known. Hardy has suggested that two reversible reactions occurring in living muscle, namely, glycogen lactic acid and phosphagen = phosphoric acid and creatine, are no longer reversible and after death proceed in one direction with the accumulation of lactic acid and creatine in the tissues.

Lactic acid has some role in the development of rigor, as rigor is usually accompanied by or preceded by increase in lactic acid. But, Moran states, under certain conditions, i.e., if an animal has been treated with insulin or iodoacetic, rigor develops without the production of lactic acid. He also adds that there are a number of chemical reactions which take place at death that have not been defined and among them will be found the cause or stimulus leading to the changes in the state of the proteins.

Time of onset of rigor. At ordinary temperatures rigor is usually complete in 10 to 12 hours. Rigor is supposed to develop more slowly at lower and more rapidly at higher temperatures. But Smith found the effect of temperature on the rate of onset of rigor to be variable.

Only skeletal muscles develop rigor. The proportion of soluble protein is sometimes given as an explanation of why some muscles develop a greater degree of rigor than others. Skeletal muscles contain a higher percentage of soluble proteins than smooth muscles. The carcass of the pig generally does not develop rigor, but occasionally one does. It is therefore interesting to surmise whether this is due to a small proportion of soluble protein or to other causes.

If there is more lactic acid than usual in the muscle of the animal when killed, as happens when an animal is hunted or a chicken is chased before killing, rigor sets in more quickly. Benson has reported that rigor sets in more rapidly in fatigued fish muscle (trawl-caught) than in the muscle of fish taken from a pen.

Changes occurring during rigor. In addition to the development of turgidity, other changes occur simultaneously, for enzyme action does not cease at the time of slaughter. There is evolution of heat known as the heat of rigor. The glycogen practically disappears from the tissues and this glycogen loss parallels the lactic acid increase. Moran states that for mammalian muscle the lactic acid reaches a value of approximately 0.8 per cent. The pH of the muscle falls from pH 7.2 or 7.4 to about pH 5.6 or 5.8, sometimes as low as pH 5.3. Because of various factors, such as amount of glycogen to form lactic acid, the pH reached during rigor varies somewhat.

It had previously been found without exception that the amount of soluble protein is decreased during rigor; but Smith found no change in solubility of the proteins in his investigation.

Passing of rigor from muscles. After a lapse of time rigor passes off. The length of time varies with the speed with which rigor developed, with different conditions and temperatures of storage, and with different animals. It may require 5 to 6 days or longer at refrigeration temperature and a shorter period at higher temperatures. It passes more rapidly from a carcass in which rigor develops early. With the passing of rigor the muscles become more soft and flexible. One observation that the author's family often made was that chickens killed and stored before cooking over night in the cellar were more tender than chickens cooked and eaten the same day they were killed. The temperature of the cellar was higher than that of a refrigerator, and the chickens were often chased before killing; these factors probably affected the time required for the passing of rigor.

The greatest physical change with passing of rigor is the increasing tenderness of the meat.

Ripened meat. Noticeable changes that characterize ripened meat, meat from which rigor has passed and which has stood some time, are increased tenderness, change in flavor, and increased ease with which juice may be pressed from the meat. The last is probably related to the increased juiciness of the cooked, ripened meat.

Emmett and Grindley have reviewed the literature on changes in meat during storage. The report of the work of Grassman is from their summary.

In experiments reported by Hoagland et al., for beef stored just above the freezing point of the meat from 17 to 177 days, it is interesting to note that all judges agreed that the flavor and tenderness of the meat are improved with 15 to 30 days of storage. With storage for 45 days and longer, they speak of an "old," "gamey," and "off" flavor. From the comments one is led to believe that they like the meat stored for 56 days better than that stored for 45 days. This was probably due to differences in the character of the quarters of beef from different animals. With longer storage the flavor was not palatable, "old" and "off" being used to describe the flavor developed.

Grassman has reported ripened meat as being more juicy, of better flavor, and more tender than unripened meat. He adds that ripening meat to the extent preferred by the English for roasting is not good for boiling, as it imparts a disagreeable flavor to the broth.

Whether one prefers the flavor of ripened meat or that of fresh meat is largely a matter of personal choice. It is hard to describe the flavor of ripened meat, probably because there are no descriptive terms which convey the same meaning to different people. Ripened meat is more acid, is richer in flavor, and has more of a high or game flavor. Ripening may also improve the flavor of the fat of the beef. The fat from some animals develops a better flavor with ripening than that of other animals. When it is improved, the flavor of the fat is more agreeable and more mellow. However, the kind of feed the animal has received, as well as the age, sex, breed of animal, and the amount of fat may influence the flavor of the meat and the fat.