Food Preservation Principles and Methods
Scope of the domain
This domain tests the principles used to extend shelf-life and the methods that apply them: heat, cold, drying, irradiation, chemicals, pH control, water activity control and packaging.
Core rules and concepts
- Preservation principles are: asepsis, removal of microorganisms, inhibition of growth, and destruction of microorganisms.
- Blanching inactivates enzymes before freezing or drying; it is not a sterilisation step.
- Pasteurisation kills vegetative pathogens and reduces spoilage organisms but does not make food commercially sterile. It usually needs refrigeration.
- Sterilisation and commercial canning destroy or inactivate spores; low-acid canned foods need high-temperature processing, often around 121°C.
- Freezing stops microbial growth but does not kill all microorganisms; thawed food can spoil.
- Drying lowers water activity; salting and sugaring also reduce available water.
- Irradiation is a cold process that reduces pathogens and insects but does not make food radioactive.
Worked example
A small unit wants bottled orange juice with fresh flavour and about three weeks of chilled shelf-life. Choose a preservation method. Reasoning: high-heat sterilisation would destroy flavour and brown the juice. The product is acidic, so vegetative pathogens are easier to control. Pasteurisation at about 72°C for 15 seconds, hot filling or clean filling, and strict chilled storage fits the target. Freezing would change the product form; chemical preservatives alone would not assure safety.
Traps that cost marks
- Calling pasteurisation sterilisation; spores can survive.
- Believing freezing kills all microbes; it only suspends growth.
- Forgetting that low-acid canned foods need much stronger heat treatment than acidic foods.
- Using blanching only for colour; its main roles are enzyme inactivation and cleaning.