The only two types of canning that are considered safe by the USDA are boiling water bath canning and pressure canning. Do not follow directions for solar “air canning or “oven canning” in which the jars are surrounded by air, not water. Foods canned using this method are at risk for the growth of spoilage bacteria and fungi, as well as botulism bacteria.
The Kerr-Cole Large Solar Panel/Propane Hybrid Stove
Pressure cooking and canning can be done easily in a reflector-only cooker, such as a panel cooker or parabolic reflector.
Barbara Kerr was a pioneer in the solar cooking movement. In the 1970s Kerr and her neighbor Sherry Cole designed the first commercial solar oven kit, a cardboard solar box cooker. Later, her home in Taylor, Arizona became the Kerr-Cole Sustainable Living Center. I feel honored to have known her.
Kerr and engineer Jim Scott conducted experiments with solar pressure canning and medical sterilization. Barbara always saw the world as the world’s poorest people see it. She wanted her inventions to be buildable by ordinary people using cheap and preferably recycled
materials easily available locally.
This large panel-style cooker was built out of four 4’ x 8’ plywood sheets covered with aluminum foil. The panels heat a huge 46-quart All-American pressure canner that has been painted black. The sterilizer has an emergency metal/spring or neoprene disk for safety pressure release. Metal disks that melt as an over-pressure safety release do not work since they melt prematurely from the solar heat that falls on the top of the vessel.
For insulation, a chicken wire cage is wrapped around the canner,
leaving an air gap for insulation. A sheet of plastic, such as a
discarded piece of mattress wrapping, is wrapped around the chicken wire cage to act as a giant cooking bag. The trick is maintaining the right balance of heat retention and venting so that the canner remains at high pressure throughout the canning period. Because pressure canners have both a temperature gauge and visible vent steam, it is easy to see when the temperature and pressure is correct.
Most importantly, the system has a back-up propane heater
designed to kick in if clouds obscure the sun during the middle of a canning run. In order for the contents to be safely sterilized, the
pressure must not be allowed to drop.
Adapted from The Sunny Side of Cooking: Solar cooking and other ecologically friendly cooking methods for the 21st century solar cookbook and The Natural Canning Resource Book: A guide to home canning with locally-grown, sustainably-produced and fair-trade foods