Written by Lavonne Meyer (former SDSU Extension Food Safety Field Specialist).
Every year there are recipes that make the canning circuit that suggest the jars can be processed in the oven. This can be dangerous because the temperature will vary according to the accuracy of oven regulators and circulation of heat. Dry heat is very slow in penetrating into jars of food. Consider picking up a hot cookie sheet with a dry potholder and then picking up another with a wet potholder. Heat transfers very quickly with the wet potholder and chances are that you will drop the cookie sheet before letting your hand burn. This illustrates how much slower heat is transferred in the oven compared to in a boiling water bath canner. Also, jars explode easily in the oven. This is a point of concern when the person doing the canning stoops over and puts their face on the same level as the jars. If the jars bump each other or explode, there is the strong possibility of burns to the face.
Open-kettle canning and the processing of freshly filled jars in conventional ovens, microwave ovens, and dishwashers are not recommended, because these practices do not prevent all risks of spoilage. Steam canners are not recommended because processing times for use with current models have not been adequately researched. Because steam canners do not heat foods in the same manner as boiling-water canners, their use with boiling-water process times may result in spoilage. It is not recommended that pressure processes in excess of 15 PSI be applied when using new pressure canning equipment. So-called canning powders are useless as preservatives and do not replace the need for proper heat processing. Jars with wire bails and glass caps make attractive antiques or storage containers for dry food ingredients but are not recommended for use in canning. One-piece zinc porcelain-lined caps are also no longer recommended. Both glass and zinc caps use flat rubber rings for sealing jars, but too often fail to seal properly.
Rely on current recommendations from USDA for safe canning practices. Use good equipment for the purpose it was designed for and you will have successful canning projects.