The general effect of each the following factors on the resistance of microbes to destruction by heat :
- Heating time-temperature relationships
Relationships exist between the temperature of heating and the time required to destroy a specified percentage of the microorganisms present. - Initial concentration of cells or spores
The greater number of cells or spores present in food, the greater the heat treatment necessary to kill all of them - Composition of the substrate in which cells or spores are heated
In general, cells and spores are most heat resistance at or near neutrality. An increase in either acidity or alkalinity hastens killing by heat, but a change toward acid is more effective than a change toward alkalinity. The nutrient substances that are present in a food may affect the resistance of microorganisms being heated in that food. - Type of microorganism
Most molds are killed by moist heat at 60°C (140°F) in 5 – 10 minutes.
Vegetative yeasts cells are usually killed by heating at 50 - 58°C (122 - 136°F) for 10 – 15 minutes. Yeast spores are usually killed by heating at 60°C (140°F) for 10 – 15 minutes.
The heat resistance of vegetative bacteria varies widely with the species. The heat resistance of bacterial spores also varies greatly with the species of bacterium and the conditions during sporulation.
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