8 hawing and tempering T Thawing has received much less attention in the literature than either chill- ing or freezing. In commercial practice there are relatively few controlled thawing systems. Frozen meat, as supplied to the industry, ranges in size and shape from complete hindquarters of beef to small breasts of lamb, although the major ity of the material is'boned-out and packed in boxes ca. 15 cm thick weigh ng between 20 and 40kg. Thawing is usually regarded as complete when he centre of the block or joint has reached0C, the minimum temperature at which the meat can be boned or cut by hand. Lower temperatures(e 5 to C)are acceptable for meat that is destined for mechanical chop- ping, but such meat is 'tempered rather than thawed. The two processes should not be confused because tempering only constitutes the initial phase of a complete thawing process. Thawing is often considered as simply the reversal of the freezing rocess. However, inherent in thawing is a major problem that does not occur in the freezing operation. The majority of the bacteria that cause spoilage or food poisoning are found on the surfaces of meat. During the freezing operation, surface temperatures are reduced rapidly and bacterial multiplication is severely limited, with bacteria becoming completely dormant below -10C In the thawing operation these same surface areas are the first to rise in temperature and bacterial multiplication can recom nence On large objects subjected to long uncontrolled thawing cycles, surface spoilage can occur before the centre regions have fully thawed Most systems supply heat to the surface and then rely on conduction to transfer that heat into the centre of the meat. A few systems use electro magnetic radiation to generate heat within the meat. In selecting a thawing8 Thawing and tempering Thawing has received much less attention in the literature than either chill￾ing or freezing. In commercial practice there are relatively few controlled thawing systems. Frozen meat, as supplied to the industry, ranges in size and shape from complete hindquarters of beef to small breasts of lamb, although the major￾ity of the material is ‘boned-out’ and packed in boxes ca. 15 cm thick weigh￾ing between 20 and 40kg. Thawing is usually regarded as complete when the centre of the block or joint has reached 0 °C, the minimum temperature at which the meat can be boned or cut by hand. Lower temperatures (e.g. -5 to -2 °C) are acceptable for meat that is destined for mechanical chop￾ping, but such meat is ‘tempered’ rather than thawed. The two processes should not be confused because tempering only constitutes the initial phase of a complete thawing process. Thawing is often considered as simply the reversal of the freezing process. However, inherent in thawing is a major problem that does not occur in the freezing operation. The majority of the bacteria that cause spoilage or food poisoning are found on the surfaces of meat. During the freezing operation, surface temperatures are reduced rapidly and bacterial multiplication is severely limited, with bacteria becoming completely dormant below -10 °C. In the thawing operation these same surface areas are the first to rise in temperature and bacterial multiplication can recom￾mence. On large objects subjected to long uncontrolled thawing cycles, surface spoilage can occur before the centre regions have fully thawed. Most systems supply heat to the surface and then rely on conduction to transfer that heat into the centre of the meat. A few systems use electro￾magnetic radiation to generate heat within the meat. In selecting a thawing