Length of time required for ripening. The length of time required for ripening varies according to the degree of ripened flavor desired, and the temperature at which the meat is stored. As the temperature is elevated the time for ripening is shortened. At temperatures a little above the freezing point of meat, 20 to 40 days seems to give the optimum flavor. Longer than 40 days gives too high a flavor for most persons. Helser says, "When ripened meat is properly trimmed and prepared there will be no mold flavor at all, but you will have a rich, juicy, tender, and well-flavored piece of meat. One trial will convince anyone."

Finished carcasses are best for ripening. Helser states that well-finished carcasses are best suited for ripening purposes. Meat from carcasses of animals that contain little fat "will get sticky, mold, and will have to be trimmed heavily to avoid the moldy flavor." The layer of fat on the outside of the prime beef and the greater quantity of fat in the muscle fibers prevent the putrefactive bacteria from developing. Ripened meat develops a growth of mold on the surface of the meat that must be removed before cooking. Helser states: "The degree of ripeness is judged largely by the length of the 'whiskers,' as the mold is sometimes called."

Changes in cooked beef due to ripening. Helser, Nelson, and Lowe have found that roasts from the same animal, refrigerated under the same conditions, show several distinct changes in cooking from that of fresh beef. All the roasts were cooked at the same oven temperature and to the same interior temperature. Roasts cooked after 10, 20, 40, and 60 days of storage show a progressively gray color in the interior of the cooked roasts. Roasts cooked to an inner temperature of 57°C. and cooked on the fifth, seventh, and tenth days of storage were a bright red color; whereas those ripened 60 days have only a little red or rose color. Roasts from calves are less red and more gray in color than roasts from older animals.

Roasts from ripened beef brown more readily - and this is true for both the fat and lean - than unripened roasts from the same animal, cooked under the same conditions. In these experiments the results of scores for palatability indicate that "in order to produce beef for roasts having the most desirable beef flavor, steers should be at least 20 months old, and preferably 30."

After the passing of rigor the roasts are more tender and become increasingly tender with length of storage. Although the tenderness of the meat increases with storage, the increase after 20 days of storage is probably not great enough to pay for the increased cost and trouble of storing.

With longer storage the roasts are more juicy. Also with ripening the quantity of juice collecting in the platter when the roast is carved is decidedly greater than for roasts cooked after 10 days or less than 10 days of storage.

The flavor of the beef improved with ripening, and the maximum development of flavor, under the refrigeration conditions used, came with 20 to 40 days of storage. For the connoisseur of flavor, this improved flavor is decidedly worth the cost of storage.

Incipient putrefaction. Much discussion has occurred concerning the presence of bacteria within muscle. Moran states that in freshly killed muscle there is usually a low bacterial count. Hoagland, McBryde, and Powick found that certain bacteria may normally be present in some carcasses of beef, but they possessed no pathological significance and did not multiply in proper cold-storage conditions. At low-storage temperatures, spoilage by bacteria is most prevalent at the surface of the meat. As has been indicated, growth is slow during rigor, for the acidity of the meat does not favor the development of microorganisms. But with increased storage of meat, the acidity of the meat is lessened or the alkalinity increases and ammonia is liberated.

Of the different tests proposed for the detection of incipient putrefaction, Baker believes that the determination of ammonical nitrogen has been the most useful and the presence of 0.02-0.025 per cent indicates the beginning of putrefaction. Thus Baker suggests that, when the pH has risen to pH 6.2 the meat has undergone deterioration.

Changes occurring in meat during storage. Changes due to enzymes. The lipolytic, amylolytic, and proteolytic enzymes act on fats, carbohydrates, and proteins, respectively. During life, these and other enzymes are concerned with the metabolic processes of the body.

Enzyme changes are usually brought about more rapidly with higher temperatures. At very low temperatures the action may be very slow and different from that at higher temperatures owing to differenes in activity of different enzymes at different temperatures. Hoagland, McBryde, and Powick have reported that the external fat and kidney fat in beef stored just above the freezing point of the meat showed increased fatty acid content and a corresponding deterioration of these fats. They found less change in the intramuscular fat, as it was protected from bacterial action, and changes in it were due to lipase enzymes. Oxidative changes in fats are of course greater in the surface fat. The surface fat in ripened meat often shows greater changes in flavor than interior fat.

Amylolytic enzymes bring about the change of glycogen to lactic acid. These changes occur rather early in storage.

Proteolytic enzymes bring about changes of the proteins to amino acids, thus increasing the amino nitrogen, or the non-protein nitrogen, or the soluble nitrogen products of the meat. Hoagland, McBryde, and Powick found that, in quarters of beef stored 14 to 177 days, the increase in amino nitrogen amounted to 3 to 7 per cent of the total nitrogen of the beef.

Autolytic changes in beef at 37°.C. Hoagland, McBryde, and Powick stored pieces of beef free from bacteria in sterile containers at a temperature of 37°C. for periods of 7 to 100 days. Considerable juice exuded from the pieces of meat, which turned brown in color. The beef was also brown on the surface for about 1/4 inch in depth, except where it touched the container, and this was bright pink in color. Hoagland has reported that this deep pink to a purplish-red color is due to hematoporphyrin. Its formation is attributed to enzymes. The meat retained its original form; the sample stored 100 days was somewhat more tender than the one stored 7 days. The changes in the meat that could be detected by the senses of sight, smell, and taste they called organoleptic changes. The odor changed with increasing age. This change they describe as "rather old but not unpleasant." The broiled 103-day sample of meat "is quite tender and has an old, highly acid, and rather disagreeable flavor, which persists in the mouth after eating; the meat is not entirely objectionable but is not appetizing." In ordinary storage conditions meat cannot be kept free from bacteria and is not stored at such a high temperature.

Chemical changes. In storage of meat the changes due to different factors such as bacteria, enzymes, etc., are brought about simultaneously. The chemical changes are the changes in the percentage of the different constituents of the meat, however these may be brought about. Stored meat usually loses weight by reason of moisture loss. The acidity increases. Emmett and Grindley found that beef refrigerated 22 days compared with meat from the same animal refrigerated 2 days at 33° to 35°F., "(1) had lost no water, (2) that the percentage of water soluble solids, the soluble, insoluble and total protein, the non-coagulable protein, the nitrogenous and total organic extractives, the forms of ash, the total nitrogen and the total phosphorus all remained practically unchanged. (3) That the only consistent real changes were a distinct increase in the total soluble and the soluble inorganic phosphorus, being 8.0 and 17.9 per cent respectively, and a decrease of 8.3 per cent in the non-nitrogenous organic extractives. (4) The nutritive value of the meat was unaltered." After refrigeration for 43 days the chemical changes in the meat were greater in number than those for the 22-day sample. When allowance was made for the moisture loss they found a definite increase in the soluble dry substance, the nitrogenous, non-nitrogenous, and total organic extractives, the total soluble nitrogen, and the soluble inorganic phosphorus. There was a slight increase in the soluble coagulable and total soluble protein nitrogen and in the insoluble and total nitrogen.

They found the cooked meats from the 43-day refrigerated sample higher in water content, therefore juicier, than the 6-day refrigerated sample. From comparisons of other losses that occurred in the cooked 43-day sample they concluded that it was as nutritious as that from the cooked 6-day refrigerated meat.