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Bacteria reproduce at regular intervals. An example might be every 20 minutes. This allows mathematical calculations to be made in order to predict how many bacteria will be present in a given time.

The growth of bacteria can give very large numbers of bacterial cells in short periods of time. It is important, especially where food storage is concerned, that we are able to slow this process to prevent spoilage.

The rate at which bacteria divide can be reduced by reducing the temperature. Keeping food in the refrigerator slows bacterial growth and food can be kept for longer before spoiling.

If food is frozen, then bacterial growth stops. However, the bacteria are not killed, so any increase in temperature would increase bacterial growth. Cooking food at a very high temperature will kill bacteria.

Microorganisms need certain conditions in order to grow. Controlling these conditions can be useful in controlling the growth of microorganisms.

• Moisture – Bacteria need moisture in order to grow. This is why they grow on foods with high moisture content such as chicken. Foods that are dehydrated or freeze-dried can be stored for much longer as the moisture has been removed.
• Food – Food provides energy and nutrients for bacteria to grow. High risk foods particularly protein foods such as chicken and dairy products are rich in nutrients and moisture and so promote bacterial growth.
• Time – If provided with the optimum conditions for growth, bacteria can multiply to millions over a small period of time via binary fission. This is when a bacterium divides in two every 20 minutes.
• Suitable pH – Most bacteria reproduce best at a neutral pH level of 7. Acidic foods with a pH below 7, or alkaline foods with a pH above 7, may stop or slow down the rate of bacterial growth.