4. Sources
General info: The types of foods involved in botulism vary according to food preservation and cooking practices. Any food conducive to outgrowth and toxin production can be associated with botulism. This can occur when food processing allows spore survival and the food is not subsequently heated before consumption, to eliminate any live cells.
Almost any type of food that is not very acidic (pH above 4.6) can support growth and toxin production by C. botulinum. Salt concentration from 4% to 5% is needed for inhibition of its spores (especially regarding type E), with a 5% concentration completely inhibiting their growth. Salt concentrations slightly lower than those providing inhibition tend to extend spore outgrowth time at low temperatures.