Why must vegetables and tomato vegetable mixtures be processed in a pressure canner?
The bacteria that cause botulism cannot grow in acid foods (foods with a pH less than 4.6), but can grow in low acid foods like vegetables, tomato vegetable mixtures, meats, poultry, and fish. These bacteria have spores that are very heat resistant. That is the reason that the only safe way to process low acid foods is in a steam pressure canner for the recommended time and pressure. If low acid foods are processed for less than the recommended time at the wrong pressure, if pressure canner gauge is not accurate, or if they are processed in a boiling-water canner, the spores of botulism-producing bacteria can survive. Inside a sealed jar these spores germinate to produce actively growing bacteria. As they grow they produce a deadly toxin which causes botulism food poisoning. Note: Tomatoes must be acidified before they are canned by boiling-water or pressure.
Barbara Willenberg, Nutritional Sciences, University of Missouri-Columbia
Last update: Tuesday, May 05, 2009