Beef fat quality
Carcass fat plays an important role in many areas of meat quality. Surface fat prevents rapid chilling of the underlying muscle tissues, thereby reducing the likelihood of cold-shortening and reducing weight loss during chilling.
Fat hardness/softness directly affects efficiency of processing and fat also contributes to the desirable eating attributes of meat. In terms of meat quality, fat quality attributes of colour, hardness and texture are important for certain markets. The quality of fat can markedly affect the carcase value at the wholesale level—particularly that for the Japanese market, which prefers soft white fat.
Yellow fat is perceived by some consumers to be undesirable, as they believe that it is an indication of meat from old or otherwise inferior cattle. However, this is not necessarily so and there is no evidence that fat colour, in its own right, affects the palatability of the cooked product.
While extended grain feeding improves fat colour and leads to greater product uniformity, in Australia it often leads to an increase in fat hardness. Feedlot cattle, particularly those destined for the Japanese market, are generally large carcases greater than 300 to 400 kg. Because of their size and the feeding regime to which they have been subjected, such carcases commonly have excessive fat thickness and fat that is often very hard when chilled. Although carcase fat of pasture-fed beef may also become hard when chilled, it is not as great a problem as with the carcase fat of grain-fed cattle. In addition, reports from Japan and the US suggest that fat from their cattle seems softer. The Japanese market highly regards fat that is soft, finely textured and with satin-like appearance. Such soft translucent fat, with its relatively low melting temperatures, contributes to desired mouth feel and flavour attributes of the meat when cooked.
The nature of fat on Australian beef carcases can vary significantly, from very soft and yellow on old cows to very hard and white on long-term grain-fed cattle. Pasture-fed and short-term grain-fed cattle, however, can have hard fat. Hard fat of beef carcases is a problem confronting the Australian meat industry, having implications in areas of industrial relations, workplace safety—including repetitive strain injuries, abattoir efficiency and meat quality.
Commercial practice requires rapid chilling of carcases after slaughter, but when carcase fat temperature falls below about 10°C it often becomes relatively hard and is more difficult to cut.
Fat tissue is composed of fat cells embedded in a connective tissue matrix. About 85% of the fat tissue is made up of triglycerides within fat cells; each triglyceride is made up of three fatty acids in a molecular form. The remainder of the fat tissue is mainly comprised of moisture (~12%) and connective tissue (~3%). Although collagen of various types and degrees of cross-linking is a major structural component of fat tissue and does affect the texture, the hardness of carcase fat at a given temperature is determined mainly by its overall fatty acid composition and by the molecular make-up of the triglycerides. Saturated fatty acids such as palmitic and stearic acids have high melting points (65-70°C) and their presence contributes to hard fat, whereas unsaturated fatty acids such as palmitoleic and oleic acids have low melting points (0-15°C) and confer softness. The overall melting temperature of fat, therefore, will depend largely on the proportion of these individual fatty acids.
Besides the fatty acid and triglyceride composition affecting hardness in its own right, fat structure at the molecular level may change with time of storage at a given temperature. Such changes in triglycerides result from molecular rearrangement of their constituent fatty acids to more stable forms and these changes are associated with hardening of fat. Thus, carcase fat will continue to harden up to a certain point, as it remains in a chiller at a constant temperature. Therefore, apart from some degree of surface drying, which also causes hardening, carcases chilled for three days are usually more difficult to bone than those chilled for 24 hours.