Figure 1-2. The four phases in the life cycle of bacteria.
c. It is obvious that time is important for the growth of harmful bacteria in food.
What is especially critical is that it takes only 4 hours for bacteria to adjust to a new
environment. Therefore, 3 hours of cumulative time is the maximum amount of time
potentially hazardous food can be in the danger zone and not be a health hazard. After
3 hours in the danger zone, enough bacteria may have grown in the food to cause
foodborne disease outbreaks. (This time accumulates--that is, each separate period of
time that the food is in the danger zone adds to the 3-hour limit.)
1-12. OXYGEN REQUIREMENTS FOR BACTERIAL GROWTH
a. The oxygen situation also effects bacterial growth. Some bacteria live only in
the presence of oxygen; other bacteria live only in its absence. Still others, including
many of those that cause foodborne disease, can grow with or without oxygen.
b. The ability of disease-producing bacteria to adjust to different oxygen
situations makes them a real threat to a food service facility. Since some bacteria can
live in or adjust to an environment without oxygen, they can grow and contaminate
foods in sealed containers, such as cans, bottles, and plastic bags or pouches.
1-13. MOISTURE REQUIREMENTS FOR BACTERIAL GROWTH
a. Moisture is a necessity for bacterial growth. Bacteria absorb food through
their cell walls. However, their cell walls cannot pass solid food. Bacteria need
moisture to break down solid food to the point where they can absorb it. Due to this,
bacteria cannot grow well in a material with a moisture content of less than 15 percent.
b. Water activity is the term used to describe the moisture content of food.
Water activity values range from 0 to 1. A food that has a water activity value below
0.85 will not support the growth of the bacteria that cause foodborne disease.