Pathogens

• Food spoils because bacteria grow in it. These bacteria are already present in all food, as well as in the air and water. However, favorable temperatures and the right conditions encourage them to grow rapidly. Some bacteria, called pathogenic bacteria, produce sickness in humans. These bacteria include Salmonella and E. coli, two of the most common food poisoning sources. Maintaining food at a temperature below 40 degrees helps keep these bacteria from reproducing to dangerous levels.
  
  

Spoilage Bacteria

• Other bacteria don't cause illness in humans, but do cause problems with the food. These bacteria may cause food to smell bad, become slimy or change color. They can also affect the taste of food. According to the U.S. Department of Agriculture, it's actually safe to eat spoiled food that has been stored at low temperatures, though most people choose not to. Spoilage bacteria can grow at refrigeration temperatures, but more slowly than on the counter at room temperature. Modern refrigerators keep the food from losing its appearance and taste as quickly because they maintain a consistent temperature inside.
  
  

Fungi

• Bacteria aren't the only organisms that can cause food spoilage. Molds, microscopic fungi, can also cause problems. These organisms grow in the food, using many tiny root threads, and develop a structure called a fruiting body on the surface. This fruiting body is the visible part. When it's covered in spores, it often develops a color. That's why moldy food may look blue, green, orange or pink. Most molds produce only an unpleasant taste or texture in food, but some actually produce poisons called mycotoxins. These toxins can make people sick or even kill sensitive individuals. Like bacteria, mold prefers warmer temperatures and grows more slowly in the refrigerator. Clean refrigerators regularly to reduce the risk of mold growth.
  
  

Considerations

• While modern refrigerators provide more consistent cooling than their ancestors, some factors can affect their function and encourage faster spoilage. In case of a power outage, leave food in the refrigerator and avoid opening it; even while it's not working, the insulation can keep food from heating up. If the outage lasts for more than about four hours, use ice blocks or dry ice to reduce the temperature inside. According to the USDA, 50 pounds of dry ice can cool an 18-cubic-foot freezer for 48 hours. Even during normal operation, avoid holding the refrigerator open for long periods or repeatedly opening and closing the door. This action lets warm air in and can increase the risk of spoilage.