Spores and toxins

Thorough cooking kills most bacteria. Two things can get past it: spores and toxins. Together they explain many of the rules in this course.

A spore is a tough protective form made by some bacteria. Spores can survive cooking. When food cools slowly, spores can become active bacteria again and multiply quickly. Bacillus cereus and Clostridium perfringens both form spores.

Think of a large pot of beef stew left on the side overnight. Cooking killed most of the bacteria, but not the spores. The warm stew then gave them everything they needed. By the morning, there could be enough to cause illness. The same thing can happen to a tray of cooked rice. Cooling food quickly is the control.

A toxin is a poison made by some bacteria as they grow in food. Staphylococcus aureus and Bacillus cereus both make toxins. Some toxins are not destroyed by cooking or reheating. Reheating may kill the bacteria but leave the poison behind.

Cooked rice shows both problems. Bacillus cereus spores can survive cooking. If the rice stays warm, the bacteria multiply and make a toxin. Reheating the rice may not destroy that toxin, even if the rice is steaming hot. So cool rice quickly, keep it chilled, and do not leave it warm for hours.

So you cannot make food safe by heating it again. Food that has been left in the danger zone for too long must be thrown away, not reheated.