Milk Pasteurization — Complete Technical Guide for Dairy Engineers
A complete technical guide to milk pasteurization — HTST, LTLT, UHT processes, time-temperature combinations, equipment, and quality effects.
What is Pasteurization?
Pasteurization is a heat treatment process that destroys pathogenic microorganisms in milk while preserving nutritional and sensory quality. Named after Louis Pasteur, it has been used commercially since the 1880s.
Goal: Destroy all pathogens (especially Mycobacterium tuberculosis and Coxiella burnetii) without damaging the product.
FSSAI/IS 1479 Pasteurization Standards
| Method | Temperature | Time |
|---|---|---|
| LTLT (Batch) | 62.8°C (145°F) | 30 minutes |
| HTST (Continuous) | 71.7°C (161°F) | 15 seconds |
| HHST | 89°C | 1 second |
| HHST | 90°C | 0.5 second |
| HHST | 94°C | 0.1 second |
| HHST | 96°C | 0.05 second |
HTST Pasteurization (Most Common)
HTST (High Temperature Short Time) is the standard commercial process for large dairy plants.
How HTST Works
- Raw cold milk enters from balance tank
- Milk preheated in regeneration section by outgoing hot milk (~90% efficiency)
- Milk heated to 72°C+ in heating section (hot water circuit)
- Milk flows through holding tube — 15-second hold time
- Temperature sensor at holding tube exit: if < 72°C, FDV diverts milk back
- Pasteurized milk cooled in cooling section by cold/chilled water
- Milk exits at 4°C for storage or further processing
Key HTST Parameters
- Flow rate: Fixed by feed pump (positive displacement)
- Holding time: = Holding tube volume / Flow rate
- Regeneration efficiency: 85–94% (reduces energy consumption)
- FDV (Flow Diversion Valve): Critical safety device — must be fail-safe
UHT (Ultra High Temperature)
UHT processing at 135–150°C for 2–4 seconds produces commercially sterile milk with 6-month ambient shelf life.
- Indirect UHT: PHE or tubular HX (no direct contact)
- Direct UHT: Steam injection or steam infusion (very rapid heating)
UHT requires aseptic packaging — typically Tetra Pak cartons or aseptic bottles.
Quality Effects of Pasteurization
| Parameter | LTLT | HTST | UHT |
|---|---|---|---|
| Vitamin B1 loss | 5–10% | 3–7% | 10–20% |
| Vitamin C loss | 5–30% | 10–25% | 20–40% |
| Vitamin B12 loss | <10% | <10% | 10–20% |
| Flavor change | Minimal | Minimal | Cooked/caramel |
| Shelf life (refrigerated) | 14 days | 14–21 days | N/A |
Phosphatase Test
The standard test to verify pasteurization is the alkaline phosphatase (ALP) test. The enzyme is inactivated by pasteurization. Positive ALP = under-pasteurization or post-pasteurization contamination.
Critical Control Points (CCP) in Pasteurization
- Pasteurization temperature — monitor continuously
- Holding time — verify via flow rate and tube dimensions
- FDV operation — test weekly
- Regeneration contamination — ensure pasteurized milk pressure > raw milk pressure
- Post-pasteurization contamination — hygienic equipment design