Interactive lesson

Clay pot cooler, step by step

Interactive lesson: a pot in a pot, wet sand and a little wind — how it works, what goes inside, the pots, making it, daily care and cleanliness.

Free sample Chapters 1 and 2 (8 steps) are free. The full lesson comes with the Clay pot cooler module. Already bought? Unlock

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The whole lesson as text

1. How it works

Two unglazed pots, one inside the other, with wet sand between them.

  1. A pot in a pot — An outer pot of unglazed, porous clay. Inside it a smaller pot for the food.
  2. Sand and hessian — The sand between the pots is kept wet all the time. The lid is wet hessian (burlap), cloth or a clay saucer.
  3. Shade and a draught — The cooler stands in the shade, in a draught. Wind carries away the damp air round the pot, and sun heats the pot faster than evaporation cools it.
  4. Dry or muggy — On a dry day roughly 5–8 °C below the air (8–12 °C in the dry interior of North America), on a muggy day only 1–3 °C; in a damp UK or Irish summer often 2–4 °C. The air inside is humid, so vegetables don't wilt.

Why: Water from the wet sand passes through the wall of the outer pot and evaporates from its surface. The heat for that comes from the sand, the inner pot and the food, so everything inside cools.

  • A clay pot cooler is not a fridge and will never hold 4 °C.
  • Measure first how much it cools where you live, and only then decide how much you rely on it.

2. What goes inside

Vegetables, fruit and leafy greens keep roughly 2–3 times longer than on the kitchen table.

  1. Tomatoes and peppers — Ripe tomatoes 5–10 days instead of 2–4. Peppers and aubergines 7–14 days, as whole fruits.
  2. Greens in a cloth — Lettuce, chard and leafy greens 2–4 days, in a damp cloth or basket. Put delicate greens along the wall, where it is coldest.
  3. Fruit apart — Ripe peaches, apricots, plums and tomatoes give off ethylene, which turns greens yellow. Keep fruit in a separate basket and use it first.
  4. Meat and milk: no — Meat, milk, fresh cheese, cream and cooked food don't go inside, not even “just until evening”. Inside it is 18–28 °C and damp in summer: ideal for bacteria.

Why: Vegetables are spoiled not just by heat but by water loss. In a clay pot cooler it is cooler and damper, so produce stays firm. In a damp climate that humidity is the main benefit.

  • Pick in the morning, while the vegetables are cool, and put them in the cooler at once.
  • Eggs don't go in a damp cooler, and onions, garlic and potatoes for storing need dry conditions.

3. Pots and sand · Locked

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4. Making it · Locked

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5. Daily care · Locked

Buy the Clay pot cooler module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.

6. Cleanliness and winter · Locked

Buy the Clay pot cooler module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.