Drying basics, step by step
Interactive lesson: why dried food keeps, the four things that decide every drying, temperatures by food, preparation, the dryness test and conditioning.
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The whole lesson as text
1. Why dried food keeps
Moulds, yeasts and bacteria need free water to grow.
- Fresh means lots of water — Fresh fruit and vegetables are 75–95 % water. An apple is 85 %, a carrot 88 %, a cep (porcini) about 90 %.
- What's left when dried — Dried food keeps 10–25 % water, depending on the kind. Fruit 15–25 %; vegetables, mushrooms and apple crisps under 10 %.
- Safe while it stays dry — Dried food is safe only as long as it stays dry. Conditioning, packing and storing are there to keep it that way.
- Mouldy stays poisonous — Drying does not destroy toxins. A mouldy pepper, fig or plum and an unidentified mushroom stay poisonous when dried.
Why: Once you draw most of the water out of food, the microbes stop and the enzymes work very slowly. The food is not sterilised: the germs stay alive but asleep, and they wake up as soon as the food takes up moisture again.
- Fruit may stay moister because sugar binds water. Vegetables and mushrooms must be dried until brittle.
- Everything you do after drying has one purpose: to keep the food dry.
2. The four things that decide
From the attic to the electric dehydrator, drying depends on the same things.
- Temperature — Too cool: the food ferments and goes mouldy. Too hot at the start: case hardening, dry outside, moist inside, mould in the jar.
- Airflow — Warm air picks up moisture, so it has to leave. Cool air comes in at the bottom, warm, moist air leaves at the top.
- Air humidity — Below 50 % outdoor humidity, drying in sun and shade goes well. Measure it with a cheap digital hygrometer.
- Thickness and time — Pieces of the same thickness, in a single layer, not touching. Don't interrupt drying while the food is still full of water.
Why: When something goes wrong, it is almost always one of them. Airflow matters more than high temperature.
- A damp, sourish smell in the dryer means there is too little air.
- Above 70 % air humidity (fog, rain, dew) the sun and shade don't dry: the food takes moisture back.
3. Temperatures by food · Locked
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4. Preparation · Locked
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5. When it is dry enough · Locked
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6. Conditioning and pasteurising · Locked
Buy the Drying basics module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.