Inherent variability in the efficacy of the USDA raw-pack process for home-canned tomatoes

A sample of home-canned tomatoes, processed by the USDA raw-pack procedure, was used to study the factors affecting the calculated lethality of Bacillus licheniformis spores. Waterbath size and canning load did not affect heat penetration rates in pint jars. Calculated lethalities between 1 and 7 log reduction were obtained with runs that varied in waterbath size, amount of water in the bath, and load size. As these variables decreased there was a concomitant decrease in come-up time, and as a result, a lower maximum cold-spot temperature. These data demonstrate that the underlying assumption of the USDA raw-pack process, i.e., that actual process time is the major determinant of process lethality, is faulty. Lethality is influenced by a multiplicity of factors. (emc)