Well and spring cooling, step by step
Interactive lesson: how cold your water is, a trough with running water, the spring house, the well, the stream and milk from milking to the pan.
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The whole lesson as text
1. How cold the water is
Water coming out of the ground is roughly the temperature of the soil at the depth it comes from.
- Hill spring — A capped spring is roughly 8–12 °C (46–54 °F) in summer; limestone springs are often 8–10 °C. It is the steadiest water.
- Dug well — A well 6–15 m deep is roughly 10–14 °C in summer. A shallow well is warmer in summer.
- Stream and river — A woodland stream is 12–18 °C and changes with the weather and rain. A river or pond is 18–25 °C in summer and no good for cooling.
- Measure your water — In the hottest week of July, measure the water with a liquid thermometer, where the containers will stand.
Why: Water cools much faster than air, but never below its own temperature. A difference of 3–4 °C between your spring and your neighbour's well decides what you can cool.
- A spring is the same all year; only the air round it changes. For cooling, only the summer figure matters.
- These are rough figures. Your water may be warmer or colder.
2. Why water cools fast
Water carries heat away about twenty times faster than still air at the same temperature.
- Air or water — A churn of milk in the air of a cellar takes 6–10 h to reach 15 °C, too slow. In running water, with stirring, 1–1.5 h.
- Smaller containers — Two 10 L churns cool much faster than one of 20 L. Bottles and jars of 1–2 L faster still.
- Water up to the neck — The water comes up to the neck of the churn, but not over the lid. The more of the container stands in water, the faster.
- Stir — Stir the milk with a clean ladle every 10 minutes. The warm middle comes to the cold wall.
Why: The closer the milk gets to the water temperature, the slower it cools, so the last two degrees take as long as the first fifteen. Water at 11 °C will not get milk below 12–13 °C.
- In still water without stirring, the water round the churn warms quickly: it takes 3–4 h to reach 15 °C.
- If you cannot let the water run, change it once: 4 L of water per litre of milk, in two fills.
3. A trough with running water · Locked
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4. The spring house · Locked
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5. The well and the stream · Locked
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6. Milk from milking to the pan · Locked
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