Contrasting Temperature Profile Development in Three Domestic Pressure Canners Operated without Venting

Effects during thermal processing of entrapped air on lethal effect were evaluated in three domestic canners with quart mason jars. Entrapped air volumes in ceramic-bead products were established with various fillings of water into a dry product matrix. Lethal effects were determined using thermocouples positioned near the bottom, middle, and top of the model product and others outside the jars. Two canners (All American and Mirro models) were continuously vented during the process while the third (National Presto) was not - but was vented de facto until the lid lock moved up under the influence of escaping gases. Higher lethal effects were noted when least product-entrapped air was modeled.