What Aging Does

Cooked, unaged beef has been described as "metallic" and lacking in typical beef flavor. Aging gives beef a flavor that has been described as "gamy." True beef flavor is fully developed after about 11 days of aging. The aged beef flavor increases with increasing aging time.

Aging also increases tenderness. It has been shown that during the aging process certain changes take place in portions of the structure of collagen and muscle fibers. Currently, it is thought that enzymatic-caused changes in the structure of muscle fibers are largely responsible for the increase in tenderness. It is known that tenderness decreases immediately after slaughter while rigor mortis takes place (taking 6 to 12 hours to complete); then tenderness increases gradually. Tenderness continues to increase up to 11 days, after which there is no increase in tenderness.

One study showed that maximum tenderness and progress of tenderization during aging varies among muscles and is associated with the color of the carcass lean. (See Animal Science folder F0-0688 for a discussion of "Dark-Cutting Beef.") In general, aging dark-cutting beef beyond seven days did little to increase tenderness. However, in carcasses where lean was lighter in color, tenderness continued to improve during up to 16 days of aging.

The tenderness effects of aging are more evident in carcasses from older animals than in the usually more tender lean from younger animals' carcasses.

Aging also decreases the shelf life of fresh meat products. Ground beef made from trimmings from aged beef carcasses usually has a shorter shelf life in the retail case and in your refrigerator, primarily because of increased microbial growth that occurs on certain parts of the carcass during the aging process.

Some research has demonstrated that as fresh meat ages, the activity of the various enzymes decreases and protective action against oxidation declines, thus increasing susceptibility to oxidation. This suggests that oxidation of fresh raw meat becomes increasingly important the more meat is aged.

During the aging process, one can also expect a loss of weight of the product. Because the lean (exclusive of trimmable fat and bone) is approximately 70 percent water, it's easy to see why there is a weight loss. The weight loss is caused by dehydration of the lean and fat. The weight loss occasionally occurs at tremendous proportions depending on relative humidity, amount of air flow and temperature of the aging cooler. During chilling of the hot carcass immediately after slaughter, the carcass will lose 2 to 3 percent of its weight because of moisture loss. Aging the carcass beyond this time will result in additional tissue shrinkage of 1 to 1.5 percent for each seven days. Carcasses with a thin external fat cover will lose more moisture than carcasses with a heavy fat cover. One study observed an 18 percent trim and shrink loss from loins aged 14 days in a 36 degrees F cooler.