Just like us, bacteria need food to grow. Nutrients, such as protein, provide bacteria with the food they need to thrive. Potentially hazardous foods, such as meat, milk, eggs and fish are all moist and protein-rich. Other foods that are potentially hazardous include legumes, potatoes, tomatoes, leafy greens, sprouts and other cut produce. All of these are a good food source for bacteria.

When small numbers of microbes are present in foods, there is little danger of getting a foodborne illness. If the microbes are left in ideal growing temperatures for long periods of time, they will multiply quickly and increase the risk of getting sick. Ideal growing temperatures are from 41 °F to 140 °F, a range called the “Danger Zone.” At home, foods should never be left in the Danger Zone for more than two hours. In restaurants and other foodservice establishments, food can spend no more than four hours at uncontrolled temperatures before it must be discarded.

Most bacteria need oxygen to grow. However, some bacteria grow best in areas that have little oxygen. Clostridium botulinum, the type of bacteria that causes botulism, does not like oxygen. Improperly canned items would be a good place for the botulism toxin to develop. Never use cans of food with bulging sides; this can be a sign that the botulism toxin is present.

Moisture is needed for microorganisms to grow. Shelf-stable foods such as flour, uncooked pasta, rice and cereal do not need to be refrigerated because they contain very little water.