Why removing water preserves
The same mechanism as salting, arrived at from the other direction. Microbes need available water; drying takes the water away entirely rather than binding it up.
The threshold matters. Partly dried food is not preserved food — it is food with less water in it, which is a very different thing, and a semi-dried fruit or an under-dried piece of meat can support growth perfectly well. This is the main way domestic drying goes wrong, and it goes wrong invisibly, because half-dry looks a lot like dry.
Drying also stops most enzyme activity, which is the other reason dried food keeps its character: the reactions that would otherwise turn it brown, soft and stale need water to proceed.
What drying does to flavour
This is the interesting part, and the reason to dry things you could easily buy fresh.
- It concentrates. Everything dissolved in the water is left behind at a higher concentration — sugars, acids, savoury compounds. A dried tomato is intensely sweet and savoury in a way a fresh one never is.
- It creates new compounds. Slow drying allows enzymatic and browning reactions to run, and the results are often the defining flavour: this is most of why a dried mushroom, a dried chilli or a dried grape smells of something the fresh one does not.
- It destroys the volatile top notes. The lightest, freshest aromas leave with the water. Dried herbs lose exactly the qualities that made fresh basil or coriander worth having, which is why those two dry so badly.
- It changes the texture permanently. Rehydrated food never returns to what it was — cell walls have collapsed and cannot be uncollapsed.
- The soaking liquid becomes an ingredient. Dried mushroom or tomato soaking water carries most of what came out, and pouring it away wastes the best part.
What dries well, and what does not
- Excellent — mushrooms
- Dry beautifully and gain enormously in savouriness. Dried porcini and shiitake are arguably better ingredients than the fresh.
- Excellent — chillies
- Change character completely, developing fruity, smoky and raisin-like notes. Every dried chilli is its own ingredient.
- Excellent — hardy herbs
- Oregano, thyme, rosemary, bay, marjoram, sage. Their aromatic compounds are relatively heavy and survive.
- Excellent — fruit
- Apricots, figs, grapes, apples, plums. Sweetness concentrates dramatically.
- Poor — soft herbs
- Basil, coriander, parsley, chives, dill. Their aroma is in volatile compounds that leave with the water, and dried versions taste of hay.
- Poor — most fresh vegetables for eating as vegetables
- They dry fine and rehydrate into something disappointing. Dry them for stock and seasoning rather than to reconstitute.
- Needs care — meat and fish
- Drying meat safely depends on salt, temperature and rate as well as on the drying itself, and is a curing question rather than a drying one.
How to dry things at home
- Cut evenly and thinly. Uneven pieces dry at different rates, and the thickest piece decides whether the batch is safe to store.
- Give everything space and airflow. Pieces touching each other stay wet where they touch. A rack beats a tray.
- Use gentle heat if any. Low oven with the door ajar, an airing cupboard, a dehydrator, or a warm dry room. High heat cooks the outside and seals moisture in — the exact opposite of what you want.
- Dry herbs in the dark. Light degrades the aromatic compounds and bleaches the colour, and it is why a jar of grey oregano tastes of nothing.
- Test for dryness properly. Properly dried fruit is leathery and does not release moisture when squeezed; herbs crumble; mushrooms snap rather than bend.
- Condition fruit before storing it. Loosely jar it for a few days and shake it daily — any remaining moisture equalises, and condensation on the glass tells you it is not dry enough yet.
- Store airtight, cool and dark. Check jars in the first fortnight, and if there is any condensation, dry the contents again.
Common questions
Do I need a dehydrator?
No. A low oven, a warm airy room or a rack in an airing cupboard all work. A dehydrator is more consistent and more convenient, not more effective.
How do I know when it is dry enough?
By texture, not by time. Leathery and non-sticky for fruit, brittle for herbs and mushrooms. If in doubt it is not dry enough — condition it in a jar and watch for condensation.
Why do my dried herbs taste of nothing?
Either they were a soft herb that does not dry, or they were dried in light or in too much heat. Dry hardy herbs, in the dark, gently.
Can I dry in the sun?
In a hot dry climate, yes — it is traditional for a reason. In a British summer, generally not: too slow and too humid, and slow drying in damp air is how things go mouldy instead.
Should I use the soaking water?
Almost always. It carries a large share of the flavour. Strain it, because grit settles at the bottom.
Try this next
- Salting the same idea by another route
- Mushroom the food drying improves most
- How to use herbs dried against fresh
- How to choose a preservation method when drying is the right answer