Food Processing and Preservation Technology
Domain 4 examines processing and preservation technology: the unit operations and hurdle principles used to make food safe and shelf-stable.
Core rules
- Preservation works by heat, low temperature, reduced aw, acidification, redox control, irradiation, competitive microflora or packaging.
- Blanching inactivates enzymes and removes surface air; it is not a sterilisation step.
- Pasteurisation kills vegetative pathogens and reduces spoilage flora but leaves spores; the product usually needs refrigeration.
- Sterilisation and UHT aim at commercial sterility; UHT plus aseptic packaging gives ambient shelf-stable milk.
- Drying lowers aw; freezing lowers temperature and water availability but does not kill microorganisms.
- Hurdle technology combines mild preservative factors so no single harsh treatment is needed.
Worked example
Milk heated at 72°C for 15 s is HTST pasteurised. Reasoning: the time-temperature combination is enough to destroy Coxiella burnetii and most vegetative pathogens, but not heat-resistant spores. The product is therefore filled hygienically and kept cold. If the same milk were UHT-treated at about 140°C for a few seconds and aseptically packed, the spore challenge would be controlled and ambient storage would become possible.
Traps
- Calling pasteurisation sterilisation; surviving spores matter.
- Believing blanching makes food sterile; it mainly stops enzymatic browning.
- Assuming freezing kills pathogens; it only stops multiplication.
- Ignoring post-process contamination, which can spoil a correctly retorted can.