According to almost every textbook on general and food microbiology (e.g., Davis et al., 1990; Brock et al., 1994; Prescot et al., 1996; Jay, 1996; Holdsworth, 1997), microbial inactivation is a process that follows a firstorder kinetics. The same fact is repeated in numerous Websites, whether they are tutorial or an official document, like the FDA-IFT 2000 comprehensive panel summary that lists thermal and nonthermal inactivation kinetic parameters of a large number of microorganisms and bacterial spores in a variety of media. The starting point of this theory is that, upon exposure to a uniform lethal temperature, the number of the affected microbial cells or spores decreases exponentially with time. Or, stated differently, the rate of inactivation is proportional to the number of cells that are still alive or the number of bacterial spores that are still viable. In what follows, we will use the term ‘organism’ or ‘microorganism’ inclusively — that is, it will refer to microbial cells and spores, especially bacterial.