Question
Pasteurization
Answer
Pasteurization is a moist-heat process that kills pathogenic and most spoilage microorganisms in a liquid (classically milk) using a temperature and time combination well below 100°C — sufficient to destroy vegetative pathogens while preserving the nutritive/organoleptic quality of the product; it is disinfection, not sterilization (spores and some heat-resistant organisms survive).
Methods:
- Holder (batch) method — 63°C for 30 minutes.
- Flash (HTST — High-Temperature Short-Time) method — 72°C for 15–20 seconds; the method most widely used commercially, as it is faster and causes even less change to taste/nutritive value.
- Ultra-High-Temperature (UHT) method — 135–150°C for a few seconds, giving a longer shelf-life product (“long-life” milk) that can be stored without refrigeration until opened.
Organisms targeted: primarily milk-borne pathogens such as Mycobacterium tuberculosis (historically the key target organism, given its relatively high heat resistance among vegetative pathogens and its transmissibility via unpasteurized milk — M. bovis), Salmonella, Brucella, Coxiella burnetii, and Listeria monocytogenes.
Verification: the phosphatase test — alkaline phosphatase, naturally present in raw milk, is destroyed by adequate pasteurization; a positive phosphatase test after processing indicates inadequate/failed pasteurization, providing a simple quality-control check.