6 Meat refrigeration level of ca. 10 organisms cm-. For example, starting with one organism cm, 27 doublings would be needed; for 10 organisms cm-2 initially, the number of doublings is reduced to 17 Contamination of carcasses may occur at virtually every stage of slaugh- tering and processing, particularly during flaying and evisceration of red- meat animals and scalding, and mainly affects the surface of the carcass. Sources of contamination have been reviewed by James et aL.(1999) Hygienic handling practices should ensure that total viable counts on the finished carcass are consistently 105-10 organisms cm or lower for red meats. Bad practices can cause counts to exceed 10" organisms cm with red meats, carcasses of good microbial quality are obtained by 1 preventing contamination from the hide 2 avoiding gut breakage 3 the adoption of good production practices that include more humane practices throughout the slaughtering system. The effectiveness of chemical and physical decontamination systems for meat carcasses has been reviewed by James and James, (1997) and James et al. (1997). Commercial systems using steam have been introduced into the usa and are claimed to reduce the number of bacteria on the surface of beef carcasses to below 1 loglo"(Phebus et al., 1997) 1.1.2 Temperature Micro-organisms are broadly classified into three arbitrary groups(psy chrophiles, mesophiles and thermophiles)according to the range of tem- peratures within which they may grow. Each group is characterised by three values: the minimum, optimum and maximum temperatures of growth Reduction in temperature below the optimum causes an increase in genera- tion time, i.e. the time required for a doubling in number. It is an accepted crude approximation that bacterial growth rates can be expected to double with every 10C rise in temperature(Gill, 1986). Below 10C, however, this effect is more pronounced and chilled storage life is halved for each 2-3C rise in temperature. Thus the generation time for a pseudomonad(a common form of spoilage bacteria)might be lh at 20C, 2.5h at 10C, 5h at 5C, 8h at 2C or 1lh at 0C. In the usual temperature range for chilled meat,-1.5-+5C, there can be as much as an eight-fold increase in growth rate between the lower and upper temperature Storage of chilled meat at 1.5+0.5C would attain the maximum storage life without any surface freezing Meat stored above its freezing point, ca. -2C, will inevitably be spoiled by bacteria. Obviously, the nearer the storage temperature of meat approaches the optimum for bacterial growth(20-40'C for most bacteria) the more rapidly the meat will spoil Work of Ayres(1960)compared the rate of increase in bacterial number on sliced beef stored at 0.5.10. 15.20 andlevel of ca. 108 organisms cm-2 . For example, starting with one organism cm-2 , 27 doublings would be needed; for 103 organisms cm-2 initially, the number of doublings is reduced to 17. Contamination of carcasses may occur at virtually every stage of slaugh￾tering and processing, particularly during flaying and evisceration of red￾meat animals and scalding, and mainly affects the surface of the carcass. Sources of contamination have been reviewed by James et al. (1999). Hygienic handling practices should ensure that total viable counts on the finished carcass are consistently 103 –104 organisms cm-2 or lower for red meats. Bad practices can cause counts to exceed 106 organisms cm-2 . With red meats, carcasses of good microbial quality are obtained by 1 preventing contamination from the hide; 2 avoiding gut breakage; 3 the adoption of good production practices that include more humane practices throughout the slaughtering system. The effectiveness of chemical and physical decontamination systems for meat carcasses has been reviewed by James and James, (1997) and James et al. (1997). Commercial systems using steam have been introduced into the USA and are claimed to reduce the number of bacteria on the surface of beef carcasses to below 1 log10 cfu cm-2 (Phebus et al., 1997). 1.1.2 Temperature Micro-organisms are broadly classified into three arbitrary groups (psy￾chrophiles, mesophiles and thermophiles) according to the range of tem￾peratures within which they may grow. Each group is characterised by three values: the minimum, optimum and maximum temperatures of growth. Reduction in temperature below the optimum causes an increase in genera￾tion time, i.e. the time required for a doubling in number. It is an accepted crude approximation that bacterial growth rates can be expected to double with every 10 °C rise in temperature (Gill, 1986). Below 10°C, however, this effect is more pronounced and chilled storage life is halved for each 2–3°C rise in temperature. Thus the generation time for a pseudomonad (a common form of spoilage bacteria) might be 1h at 20°C, 2.5 h at 10°C, 5 h at 5 °C, 8 h at 2 °C or 11 h at 0 °C. In the usual temperature range for chilled meat, -1.5–+5 °C, there can be as much as an eight-fold increase in growth rate between the lower and upper temperature. Storage of chilled meat at -1.5 ± 0.5 °C would attain the maximum storage life without any surface freezing. Meat stored above its freezing point, ca. -2 °C, will inevitably be spoiled by bacteria. Obviously, the nearer the storage temperature of meat approaches the optimum for bacterial growth (20–40 °C for most bacteria) the more rapidly the meat will spoil.Work of Ayres (1960) compared the rate of increase in bacterial number on sliced beef stored at 0, 5, 10, 15, 20 and 6 Meat refrigeration