Microbiology of refrigerated meat 7 5C. The meat developed an off odour by the third day at 20C, the tenth day at 5C and the 20th day at 0C. Similar data has been reported by other workers. They clearly demonstrate the effectiveness of refrigeration in reduc ing the rate of increase in bacterial numbers and extending shelf-life As bacteria generally grow more rapidly than fungi, mould spoilage of meat is thought to develop only when competing bacteria are inhibited. Temperature is usually assumed to be the critical factor, mould spoilage being typically associated with frozen meat. It has been generally accepted that moulds can develop on meat at temperatures as low as -10 or-12C. There is some evidence that this is an exaggeration and that for practica purposes the minimum temperature for mould growth on meat should be taken to be ca. -5C(Lowry and Gill, 1984). It is further thought that surface desiccation, rather that temperature, is the factor that inhibits bac terial growth. If this is the case then mould growth on frozen meats is indica tive of particularly poor temperature control. Many factors influence the growth and survival of micro-organisms in meat during freezing and frozen storage. However, the main factor affect ing the growth of micro-organisms during freezing is the availability of water Until the temperature is reduced below the minimum temperature for growth, some micro-organisms have the potential to multiply. While most of the water in meat is turned to ice during freezing, there is always some free liquid water available, 26% at-5C, 18% at -10C, 14% at -18C, 10% at-40C (Rosset, 1982). The transformation of water into ice significantly modifies the growth environment for micro-organisms, since solutes become concentrated in the remaining free water to the level that microbial growth is inhibited. Below the freezing point of the meat, the water activity is progressively reduced preventing microbial growth(Fig. 1.0 0.9 .8 0.7 Fig. 1.1 Water activities(aw)of meat at various sub-freezing temperatures(source Leistner and Rodel, 1976)25 °C. The meat developed an off odour by the third day at 20 °C, the tenth day at 5 °C and the 20th day at 0 °C. Similar data has been reported by other workers.They clearly demonstrate the effectiveness of refrigeration in reduc￾ing the rate of increase in bacterial numbers and extending shelf-life. As bacteria generally grow more rapidly than fungi, mould spoilage of meat is thought to develop only when competing bacteria are inhibited. Temperature is usually assumed to be the critical factor, mould spoilage being typically associated with frozen meat. It has been generally accepted that moulds can develop on meat at temperatures as low as -10 or -12 °C. There is some evidence that this is an exaggeration and that for practical purposes the minimum temperature for mould growth on meat should be taken to be ca. -5 °C (Lowry and Gill, 1984). It is further thought that surface desiccation, rather that temperature, is the factor that inhibits bac￾terial growth. If this is the case then mould growth on frozen meats is indica￾tive of particularly poor temperature control. Many factors influence the growth and survival of micro-organisms in meat during freezing and frozen storage. However, the main factor affect￾ing the growth of micro-organisms during freezing is the availability of water. Until the temperature is reduced below the minimum temperature for growth, some micro-organisms have the potential to multiply. While most of the water in meat is turned to ice during freezing, there is always some free liquid water available, 26% at -5 °C, 18% at -10 °C, 14% at -18 °C, 10% at -40 °C (Rosset, 1982). The transformation of water into ice significantly modifies the growth environment for micro-organisms, since solutes become concentrated in the remaining free water to the level that microbial growth is inhibited. Below the freezing point of the meat, the water activity is progressively reduced preventing microbial growth (Fig. Microbiology of refrigerated meat 7 –30 –20 –10 0 Temperature (°C) 0.7 0.8 0.9 1.0 Water activity ( aw) Fig. 1.1 Water activities (aw) of meat at various sub-freezing temperatures (source: Leistner and Rödel, 1976)