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Why Is Heating Good in Killing Microorganisms?

Microorganisms, like other living things, survive in a certain temperature range. Temperatures that are too cold won't kill the microorganisms but will slow down their metabolism and inhibit reproduction. However, heat does kill microorganisms. According to the Community College of Baltimore County, temperatures between 112 to 160 degrees Fahrenheit will kill many microorganisms. However, some bacteria produce spores, structures that help them resist high heat. Killing those bacteria requires a temperature of 250 degrees Fahrenheit.

  1. Moist Heat

    • Moist heat is more effective than dry heat because moist heat penetrates the microbial cells, destroying the proteins and enzymes in the cells. Boiling water will kill most microorganisms after 10 minutes, according to the Community College of Baltimore County. However, the hepatitis virus may survive up to 30 minutes in boiling water and some Clostridium and Bacillus species may survive longer. This means that while boiling will destroy most germs found in food and in your household, medical instruments need to be sterilized at higher temperatures.

    Moist Heat Under Pressure

    • A higher temperature than can be achieved by boiling is needed to destroy bacterial endospores. A pressure cooker can produce the 250 degrees Fahrenheit needed to kill more resistant bacteria. The length of time items must be processed under pressure depends on the size of the items and the type of bacteria present. In home canning, pint jars are processed for 20 to 45 minutes, depending on the contents.

    Dry Heat

    • Dry heat works by dehydrating the microorganism cells. Without moisture, they can't survive. However, higher temperatures are needed for a longer time than moist heat requires. Foods cooked in the oven need to be cooked long enough to reach a high enough internal temperature to kill harmful bacteria that cause food-borne illnesses. For beef, the minimum internal temperature is 145 degrees; for pork and ground beef, ground veal or ground lamb, the temperature should be 160 degrees, and poultry should be cooked to an internal temperature of 180 degrees. The only way to be sure you have cooked meat long enough is to use an instant-read thermometer.

    Sterilizing with Dry Heat

    • To sterilize instruments, the instruments must be clean and dry. Wrap them in heat-proof wrapping paper or put them in heat-proof trays. To sterilize the instruments, they have to be brought to the appropriate temperature in an oven and maintained at that temperature long enough to kill all microorganisms. For instance, they should be heated to 340 degrees Fahrenheit and kept at that temperature for an hour. If the temperature is lower, the instruments have to be heated longer. So, if you heat them to a temperature of 285 degrees Fahrenheit, they must stay at that temperature for three hours, according to Engender Health.

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