Thermal processing

Thermal processing uses controlled heat to reduce microorganisms or inactivate enzymes in food, extending shelf life or improving safety. Its effects depend on temperature, duration, food composition, and packaging.

Thermal death time: The time required at a specified temperature to destroy a defined proportion of microorganisms. It quantifies how long a food must remain hot to achieve a chosen microbial reduction.
Pasteurization: A heat treatment that reduces pathogens and spoilage organisms without achieving commercial sterility. It is used when refrigeration or another preservation method will control surviving organisms.
Thermal resistance of microorganisms: The capacity of microorganisms to survive exposure to heat under specified conditions. Differences in resistance determine the treatment needed for each food and target.
High-pressure processing: A preservation method that uses intense pressure to inactivate many microorganisms, often with little heating. It can reduce heat-related quality changes, though bacterial spores often remain resistant.
D-value: The time at a fixed temperature needed to reduce a microbial population by 90%. It expresses the rate of microbial destruction during a constant-temperature treatment.
Commercial sterility: A condition in which viable microorganisms capable of growing in a food under normal storage conditions are absent or controlled. Canned foods are processed to achieve this condition, not absolute sterility.
Clostridium botulinum: A bacterium whose spores can grow in oxygen-free conditions and produce the potent botulinum neurotoxin. Its spores are a key safety target in low-acid canned foods.
Ohmic heating: A method that heats food by passing electric current through it. It can heat some foods more uniformly and rapidly than conventional surface heating.
z-value: The temperature increase that changes a microorganism’s D-value by a factor of ten. It shows how strongly a target organism’s heat resistance changes with temperature.
Retort processing: The heating of sealed food containers in a pressure vessel to achieve commercial sterility. It makes shelf-stable canned foods by heating the sealed package.

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