Non-uniformity in process quality was investigated during in-pack thermal sterilization of food products. This was accomplished through the combined application of the Monte Carlo procedure and a reliable mathematical method for process evaluation. Despite the large coefficients of variation found, the optimum quality process could be designed. The influence of the statistical variability of heating rate index on the retention of green beans' color was studied and an optimum temperature range was found between 125 and 135 degrees C. The variability in hardness of sterilized white beans, resulting from uncertainties of the combined effect of heating rate index and initial hardness of beans, was also evaluated by simulation. In this case, an optimum global temperature range between 120 and 135 degrees C was found, independently of the rotation, F-0 value and surface heat transfer coefficient assumed. (c) 2005 Elsevier Ltd. All rights reserved.