Canning, Food Safety Glossary

A preservation method that seals food in airtight containers and heat-processes it to destroy micro-organisms, with low-acid foods requiring strict control of Clostridium botulinum. Canning is a preservation method in which food is sealed in an airtight container, such as a can or jar, and heat-processed so that micro-organisms are destroyed and the sealed container prevents recontamination. Done correctly, canning produces shelf-stable food that keeps for a long time without refrigeration. The heat process must be matched to the food, because the acidity of the food determines how much heat is needed to make it safe. The critical safety concern in canning is Clostridium botulinum, a bacterium that forms heat-resistant spores and can grow and produce a deadly toxin in the low-oxygen environment inside a sealed container. High-acid foods, such as many fruits, can be processed at lower temperatures because the acid controls the bacterium, but low-acid foods, such as vegetables, meat and fish, must reach a high enough temperature, typically requiring pressure processing, to destroy the spores. Under-processing low-acid canned food is a serious botulism risk. Commercial canning of low-acid foods is a highly technical process that must reliably achieve the required time and temperature to destroy Clostridium botulinum spores, and is generally beyond simple home or small-kitchen equipment. Australian producers making shelf-stable canned or bottled low-acid foods need validated processes, appropriate equipment and controls, and should treat the heat process as a critical control point in their food safety program. Businesses should be cautious about producing low-acid canned or bottled products, including many vegetables, meats and some sauces, without expert process validation. Damaged, bulging or leaking cans should never be used or sold, as these can indicate spoilage or gas from bacterial growth. Where a business is not equipped to process low-acid foods safely, keeping the product refrigerated or choosing a different preservation method is safer. A small producer wanting to sell bottled low-acid vegetables seeks expert advice and finds the product needs a validated pressure heat process to destroy Clostridium botulinum spores, which its kitchen cannot reliably achieve. It instead switches to a high-acid pickled recipe with a controlled low pH, or sells the product as a refrigerated line with a short use-by date.