Meat Science

PHYSICAL CHANGES IN CHILLED MEAT

• Meat undergoes certain superficial changes as a result of storage, chief of which are shrinkage, sweating and loss of bloom.

Shrinkage

• Shrinkage or loss of weight occurs as a result of evaporation of water from meat surface; carcass cut into quarters dissipate water vapour rapidly and continuously and retail joints even more so.
• On the other hand the evaporation inhibited by membranes such as the pleura and peritoneum and in well nourished carcass, by the solidification of the superficial fat and drying of the connective tissue.
• A freshly killed carcass dissipates body heat slowly, usually 1.5 to 2.0% of weight by evaporation during the first 24 hours of hanging.
• Further loss of weight during storage depends on the humidity of the storage room, the drier the air the greater being the evaporation.
• Avoidance of all evaporative weight losses by high humidity facilitates the formation of moulds, so an accurate balance between temperature and humidity must be maintained: the dry impervious film on the carcass surface is perhaps the best protective against the growth of spoilage organisms.

Sweating

• Denotes condensation of water vapour on meat brought from a cold store into ordinary room temperature.
• The condensation occurs because of the cold refrigerated carcass lowers the temperature of the air to below the dew point.
• In winter months in Britain the dew point is generally below 4.5˚C and sweating is unlikely to occur, but in summer the dew points is always over 7˚C and moisture will be deposited on the carcass.
• If the quarter or side is cut up immediately after removal from the chilling room the sweating will be extended to the individual joints.

Loss of bloom

• Bloom is defined as the colour and general appearance of the carcass surface when viewed through the semitransparent layer of connective tissue, muscle and fat, which form the carcass surface.
• If these tissues become moist, the collagen fibers in the connective tissue swell and become opaque and the meat surface assume a dull, lifeless appearance.
• Loss of surface bloom in beef carcasses may also be caused by dehydration or undue oxidation, but it may be prevented by avoiding temperature fluctuation that permit alternate drying and dampening of the carcass surface.
• It is also important to keep the relative humility of cooling chamber high and ensure that there is circulation of air.
• Muscular tissue also tends to become brownish on exposure to air as myoglobin changes to the brown pigment metmyoglobin, but the actual amount of exposed muscle in a side of beef is so small that is of little or no consequence.
• Refrigeration has little effect on the carcass fat except in the case of frozen meat, which has undergone a prolonged period of storage.