C. botulinum grows in foods that are not acidic. The organism will grow in canned vegetables, meats, seafoods, and in chili peppers, garlic, and spices. Tomatoes are a special case. Tomatoes are usually acidic enough to prevent C. botulinum from growing. However, some varieties and some canning procedures may result in canned tomatoes that are at risk of supporting growth.
Acidity is measured with a pH meter or with pH paper strips.
C. botulinum cannot grow at a pH of 4.5 or less. C. botulinum is an anaerobic organism. This means that it does not grow in the presence of oxygen. However, I caution the reader not to think that a food has to be in a tightly sealed glass or metal container to be anaerobic. Foods that are resealed into plastic bags can be sufficiently anaerobic to support the growth of C. botulinum .