Home Processing of Acid Foods in Atmospheric Steam and Boiling Water Canners

Home canning is increasingly popular. We determined the efficacy of a boiling water canner (BWC) versus an atmospheric steam canner (ASC) in home canning of various acid foods. Research-tested recipes were followed, and temperature was tracked every 1 min with thermocouples placed at the experimentally determined cold spot for each product and in the heating medium. Time-temperature curves were plotted for at least three runs for each product in each canner, with 12 thermocouple tracings per product, through heating and air-cooling until internal temperature reached 130°F (54°C). Heat penetration rates during heating (fh) and cooling (fcl) were calculated. Total integrated lethality, F180°F (82.2°C), and lethality during heating (Fh) and cooling (Fcl) were calculated. Across all food products, fh < fcl. Fcl was the majority contributor to F180°F, ranging from 48% to 95%, for chocolate raspberry sauce and applesauce, respectively. Canner type did not significantly impact lethality (P > 0.05) in the canning of applesauce, tomato juice, and cranberries. F180°F for chocolate raspberry sauce was greater in a BWC than in an ASC (P < 0.05), but this was the result of differences in the initial food temperature, not in the canner type. Regardless of canner type or food product, calculated lethality, F180°F, was far in excess of the required 5 log reduction for spores in tomato juice and for vegetative cells in other products. Our research suggests that there is a wide margin of safety for approved home canning processes for high-acid foods processed in either a BWC or an ASC. An ASC can be safely used for home canning foods that have a pH < 4.6, with the following stipulations: a current recipe research tested for a BWC must be followed with processing time in the ASC beginning as soon as the measured temperature inside the dome reaches the boiling point of pure steam (~212°F), and jars must be allowed to air-cool unimpeded on the countertop to ensure lethality.