Engineering
Pasteurization Temperature-Time Calculator — HTST & LTLT
Calculate pasteurization equivalence using the Bigelow D and Z concept. Verify HTST (72°C/15s) and LTLT (63°C/30min) thermal process adequacy for dairy.
Formula
actualTime * Math.pow(10, (actualTemp - refTemp) / zValue)
actualTemp
Actual Process Temperature (°C)
actualTime
Actual Holding Time (seconds)
refTemp
Reference Temperature (T_ref) (°C)
zValue
Z-Value of Target Organism (°C)
Worked Example
1
Given:
actualTemp = 75
actualTime = 10
refTemp = 72
zValue = 5
2
Apply the formula:
actualTime * Math.pow(10, (actualTemp - refTemp) / zValue)
3
Result:39.81 seconds
HTST vs LTLT Pasteurization
India’s FSSAI and IS 1479 recognise two standard pasteurization processes:
| Process | Temperature | Time | Standard |
|---|---|---|---|
| LTLT (Batch) | 63°C | 30 minutes | IS 1479, FSSAI |
| HTST (Continuous) | 72°C | 15 seconds | IS 1479, FSSAI |
| UHT (Sterilization) | 135–150°C | 2–6 seconds | FSSAI |
| ESL (Extended Shelf Life) | 125–130°C | 4–16 seconds | International |
D-Value and Z-Value
- D-value: Time at a given temperature to reduce microbial count by 90% (1 log cycle). For Coxiella burnetii (the reference organism for pasteurization), D₇₁.₇ = 3 seconds.
- Z-value: Temperature increase to reduce D-value by 10×. For C. burnetii: Z = 5°C
Thermal Equivalence Formula
To find the equivalent time at a target temperature T_ref:
t_ref = t_actual × 10^((T_actual − T_ref) / Z)
Example: Is 75°C for 10 seconds more effective than 72°C for 15 seconds?
t_ref at 72°C = 10 × 10^((75−72)/5) = 10 × 10^0.6 = 10 × 4.0 = 40 seconds at 72°C
Yes — 40 seconds at 72°C is far more effective than 15 seconds.
Pasteurization Efficiency
A properly designed HTST system must deliver:
- ≥ 6D reduction of Coxiella burnetii (minimum regulatory requirement)
- Milk phosphatase test: negative (phosphatase inactivated = adequate pasteurization)
- Peroxidase test: positive (peroxidase should survive HTST — inactivated = over-heating)
Critical Control Points in HTST
- Flow Diversion Valve (FDV): Automatically diverts under-pasteurized milk if temperature drops below set point
- Temperature sensor calibration: Calibrate weekly against NIST-traceable reference
- Holding tube: Length sized to ensure minimum 15s at maximum flow rate
- Booster pump: Ensures forward pressure differential (product side > regeneration side)
Holding Tube Length Calculation
L (m) = v_max × t_hold
Where:
- v_max = maximum fluid velocity in tube (m/s) = Flow rate / (π/4 × D²) × correction for velocity profile
- For tubular flow with plug flow assumption, correction factor ≈ 2 (fastest streamline travels 2× average)
- t_hold = required holding time (15 seconds for HTST)