A generalized linear-Bigelow model was proposed to describe the effects of both temperature and pH on spore heat resistance. The model required only 3 parameters, each having a physicochemical significance. In addition to the conventional z value, the effect of pH on thermal resistance of spores was characterized by a zpH value. Although the model neglected interactions between temperature and pH, its goodness of fit and its robustness enable it to be applied for optimization of heat treatments. Further experiments need to be undertaken to validate the model under industrial conditions.