Bacterial Growth

Food.

Bacteria require food in order to grow. They like many of the foods we do. Foods with sufficient amounts of protein are best for bacterial growth. These include meats, poultry, fish, dairy products, and eggs, as well as some grains and vegetables.

Moisture.

Bacteria require water in order to absorb food. Dry foods do not support bacterial growth. Foods with a very high salt or sugar content are also relatively safe, because these ingredients make the bacteria unable to use the moisture present.

Temperature.

Bacteria grow best at warm temperatures. Temperatures between 41°F and 135°F(5°C and 57°C) promote the growth of disease-causing bacteria. This temperature range is called the Food Danger Zone.

Acidity or alkalinity.

In general, disease-producing bacteria like a neutral environment, neither too acidic nor too alkaline. The acidity or alkalinity of a substance is indicated by a measurement called pH. The scale ranges from 0 (strongly acidic) to 14 (strongly alkaline). A pH of 7 is neutral. Pure water has a pH of 7.

Oxygen.

Some bacteria require oxygen to grow. These are called aerobic. Some bacteria are anaerobic, which means they can grow only if no air is present, such as in metal cans. Botulism, one of the most dangerous forms of food poisoning, is caused by anaerobic bacteria. A third category of bacteria can grow either with oxygen or without it. These bacteria are called facultative. Most bacteria in food that cause disease are facultative.

Time.

When bacteria are introduced to a new environment, they need time to adjust to their surroundings before they start growing. This time is called the lag phase. If other conditions are good, the lag phase may last about 1 hour or somewhat longer.

If it weren’t for the lag phase, food-borne disease would be much more common than it is. This time delay makes it possible to have foods at room temperature for very short periods in order to work on them.