A distribution in food product thermal properties will produce a distribution in product temperature throughout a heating or cooling process. This in turn will cause a permanent dispersion in product quality through the mechanism of the temperature sensitivity of product quality thermal degradation kinetics. To guarantee acceptable food safety, the slowest heating product must receive adequate thermal treatment, implying that the majority of the products are over-cooked. Strategies to ameliorate this problem are suggested by determining the optimum processing temperature to minimize the final quality dispersion. As an example, the batch sterilization of packaged foods is analyzed and described by a set of three partial differential equations for (i) the heat transfer, (ii) the quality change and (iii) the microbial reduction. In this case process optimization aims to reduce the final standard deviation in quality (without affecting the final safety) by optimizing schedules for the retort temperature. (C) 2003 Elsevier Ltd. All rights reserved.