Sterilization of foods by the application of heat can be done either in sealed containers or by continuous-flow techniques. Traditionally it is an in-container process, although there have been many developments in container technology since the process was first commer cialized at the beginning of the nineteenth century Whatever the process, the main concerns are with food safety and quality. The most heat resistant pathogenic bacterium is Clastridium botulinum; this will not reproduce below a pH of4.5. On this basis, the simplest classification is to categorize foods as either acid foods (pH 4.5) or low-acid foods (pH 4.5). Note that a broader classification has been used for canning: low acid, pH >5.0; medium acid, pH 4.5 to 5.0; acid, pH 4.5 to 3.7; and high acid, below pH 3.7. However, as mentioned earlier, the main concem is with foods where pH is greater than 4.5 (Section 24). For such foods the minimum recommended process is to achieve 12 D reductions for Clostridium botulinum. known as the minimum botuli num cook. This requires heating at 121oC for 3 minutes, measured at the heating point (Section 2.4). The evidence that this provides a safe level of processing for thermally processed foods is provided by the millions of items of commercially processed foods con- sumed worldwide each year without any botulinum-related problems. The temperature of 121.1 C (250 F) is taken as a reference temperature for sterilization processes. This is used in conjunction with the e-value for Cl botulinum, which is taken a 10°C, to construct the standard lethality tables OTable Since lethaliti possible to sum the lethalities for a process and determine the total integrated lethal effect which is known as the Fo alue. This is a common method to evaluate and compare the microbiological severity of diff erent processes