Pasteurize milk by holding all of it at 145°F (63°C) for 30 minutes, then cooling it quickly below 40°F; the factory equivalent holds 161°F (72°C) for 15 seconds. Each setting is a temperature and a time that only work together, so reaching 145°F for a moment, or holding for 30 minutes at a lower temperature, is not pasteurization, and a water-jacketed pot can deliver the 30-minute batch hold reliably but a pan cannot deliver the 15-second flash hold.
Part of Dairy Production at Scale
Pasteurization is a controlled heat treatment that kills the disease organisms in milk while leaving most of its food value; it is defined by a fixed temperature and hold time, not by how hot the milk feels.
Two Established Pairs, Each Meaningless Without Its Partner
The parent article gives two settings: batch pasteurization at 145°F (63°C) for 30 minutes, and flash pasteurization at 161°F (72°C) for 15 seconds. The companion article Dairy Fermentation lists the same two as the low-temperature long-time and high-temperature short-time options. These are also the standard public-health figures for pasteurized milk.
| Method | Temperature | Hold time | Practical in a village? |
|---|---|---|---|
| Batch (vat) | 145°F (63°C) | 30 minutes | Yes, with a water-jacketed pot and a checked thermometer |
| Flash (HTST) | 161°F (72°C) | 15 seconds | Not with a pan; see below |
Heat kills bacteria as a function of both temperature and time. The pairs were set so that the most heat-resistant disease organism then known in milk is destroyed with a margin. They are not a curve you may read between: a lower temperature does not become safe just because you hold it longer, and nothing in this wiki sources a third pair, so do not interpolate one. If the thermometer or the clock fails, boil the milk instead.
Fat and sugar protect bacteria from heat. Cream and other rich or sweetened products are held at a higher setting than plain milk in the public-health tables. This wiki has no sourced figure for that setting, so pasteurize the whole milk first and make cream from the pasteurized milk afterward. See Cream Separation Techniques.
What You Need
- A pot set inside a larger pot of water (a double boiler), or a water-jacketed vat, so the milk is heated by water and cannot scorch on a direct flame
- A thermometer you have checked against ice water (0°C) and boiling water (100°C at sea level, lower at altitude) before first use
- A lid, a clean stirring paddle and a clock
- A cold-water or ice bath for cooling; see Rapid Cooling Without Refrigeration
- A log sheet: date, batch volume, time at 145°F, time the hold finished
Method: Batch Pasteurization
Step 1: Fill the jacket and the milk vessel. Fill the milk vessel no more than three-quarters. Heat the surrounding water; milk heats slowly and evenly this way.
Step 2: Stir while heating. Stir frequently so the milk at the wall and the milk at the center are the same temperature. Stirring is not optional: the thermometer reads only where its bulb sits, and unstirred milk at the wall runs hotter than milk at the center.
Step 3: Start the clock only when the coldest milk reaches 145°F (63°C). Put the thermometer bulb in the middle of the milk without touching the pot, and read it during stirring. Heating time does not count towards the 30 minutes.
Step 4: Hold 30 minutes at 145°F (63°C) or above. Keep the lid on. The lid and the upper wall must also be hot, because milk splashed above the liquid line has not been treated; a hot lid dripping condensate back in is correct, a cold lid is a contamination. If the temperature drops below 145°F at any point, start the 30 minutes again from zero.
Step 5: Cool at once. Move the vessel to the cold bath and stir until the milk is below 40°F. Do not leave pasteurized milk warm: survivors and anything it meets afterward multiply as fast as in raw milk.
Step 6: Use clean containers afterward. Pasteurized milk poured into an unwashed bucket is raw milk again.
For cheese, stay near 145°F rather than far above it: milk heated well beyond the pasteurization setting sets a weaker curd.
Worked Example: The Fuel Cost Of 20 Liters
The constants are standard physical values rather than wiki figures: milk specific heat about 3.93 kJ per kg per degree and density about 1.03 kg per liter, water 4.19 kJ per kg per degree, and air-dry wood about 15 MJ per kg burned at roughly 30% useful efficiency in an open stove. Those last two are assumptions, not measurements.
- Milk: 20 L × 1.03 = 20.6 kg, heated from 15°C to 63°C (a rise of 48°C): 20.6 × 3.93 × 48 = 3,886 kJ.
- Water jacket: 20 kg heated from 15°C to 70°C (a rise of 55°C): 20 × 4.19 × 55 = 4,609 kJ.
- Total: 8,495 kJ, about 8.5 MJ.
- Wood: 15 MJ/kg × 0.30 = 4.5 MJ useful per kg, so 8.5 ÷ 4.5 = about 1.9 kg of dry wood per batch, plus whatever it takes to hold temperature for 30 minutes.
Why The Flash Method Is Not A Pan Method
The parent article says flash pasteurization is “harder to control temperature precisely over a fire”, which is correct, but it is also not a small-batch method at all. Factory flash pasteurization is a continuous flow: milk is heated in a heat exchanger and then travels through a holding tube that is sized so every part of the flow spends at least 15 seconds at 161°F.
Sizing that tube is the hard part. In smooth (laminar) flow in a pipe, the fluid at the center moves at about twice the average speed. A tube sized for a 15-second average transit would give the center only about 7.5 seconds, which is half the required hold. Commercial plants size the tube for the fastest-moving fluid and add a valve that sends under-heated milk back for reheating. A pan, a ladle and a watch can reproduce neither. If you stir a pan to 161°F and count 15 seconds, the milk near the wall is hotter and the milk near the thermometer is whatever the thermometer says. Use the batch method.
No Thermometer, Or A Thermometer You Do Not Trust
Bring the milk to a full boil, stirring, and take it off the heat when it foams. A boil is above both settings and needs no instrument; the Boiling article covers the method. It scorches easily and changes flavor, but it is the correct fallback. The reverse is not true: a thermometer that reads high by 3°C leaves milk at 60°C when you think it is at 63°C, and 60°C for 30 minutes is not one of the established settings.
Common Mistakes
- Quoting the temperature without the time. “Heat to 145°F” is not an instruction; “hold at 145°F or above for 30 minutes” is.
- Counting the heat-up time as part of the hold.
- Heating milk directly on the flame. It scorches, and scorched film insulates the milk from the heat.
- Pasteurizing then pouring into an unsanitized pot or cooling in a dirty bath.
- Treating pasteurized milk as shelf-stable. It spoils, and ordinary storage rules apply; see Milk Handling & Safety.
Safety
Under-heated milk is raw milk with false confidence
Raw milk can transmit tuberculosis, brucellosis and listeria, and the only protection is the full temperature held for the full time. Never state, log or teach a pasteurization temperature without its hold time, never shorten the hold, and never use a thermometer you have not checked. Hot milk and boiling water scald: lift lids away from your face and keep children out of the processing area.
What’s Next
- Learn next: Cream Separation Techniques — what to do with the pasteurized milk
- Combine with: Zoonotic Diseases — the diseases pasteurization is protecting against