Drying fruit and herbs: air, sun, oven

Microorganisms need freely available water. Drying removes so much water from the food that they can no longer grow. Warm air can hold more water vapour than cold air, and moving air carries away the moist air right above the fruit and replaces it with drier air. That is why the combination of warmth, air movement and dry air is so effective.

Water travels from the inside to the outside and evaporates at the surface. Thin slices have a short path and a lot of surface – they dry quickly and evenly. Thick pieces dry slowly, and if it is too hot, the surface can harden while moisture is still trapped inside.

The damper the air and the thicker the pieces, the slower it goes – and the higher the risk that mould is faster than the drying. The food is only done when it is dry inside as well.

Cleanliness first: clean hands, knife, board and rack, wash the fruit, and generously cut away bruised and rotten parts. Use sound, ripe fruit and herbs from shops or your own garden. Foraged wild plants without reliable identification do not belong on the drying rack.

Cut evenly thin slices so that they are all done at the same time, and spread them in a single layer with gaps. Light-coloured fruit such as apples turns brown in the air because the flesh reacts with oxygen. A short dip in water with a little lemon juice helps against browning – this is only for colour, not for safety.

When air-drying in the sun, cover the fruit with a fine cloth against insects and bring it in at night, because dew can form overnight. In the oven, work at a low temperature and leave the door slightly open so that moisture can escape. Hang herbs in small bunches upside down in an airy, shady place.

Fruit is done when it is leathery and pliable and no moisture appears at the tear when you pull a piece apart. Herbs rustle and crumble between your fingers. Let everything cool completely before checking, because warm fruit feels softer than it is.

Then comes an important intermediate step, conditioning: put the cooled dried food loosely into a jar and shake it daily for a few days. Some pieces are drier than others, and this way the remaining moisture evens out. If moisture forms on the glass, it was not dry enough yet and must be dried further.

Only then do you store it sealed, dark and cool, and label the jar with contents and date. Sealing too early is a common mistake that leads to mould in the jar.

Meat, fish and game are not simply dried in the air or sun. Pathogens can survive drying. Recognised bodies such as the US National Center for Home Food Preservation require an additional heating step following tested instructions. This entry deliberately gives no instructions for dried meat.

If dried food goes mouldy or smells musty, it is thrown away – not just the visible spot. Incompletely dried fruit can go mouldy in the jar, so it is worth looking into the jar even after weeks.

Sun drying works well in dry, hot climates. In damp Central European weather it often fails because the air is too humid and the nights too cool. Then an oven or dehydrator is the more reliable choice. A dehydrator with a fan and thermostat dries more evenly and independently of the weather, but needs electricity.

Dried food is light, compact and keeps without refrigeration – ideal for surpluses from the garden. Some of the vitamins are lost in drying. Exact temperatures and times for individual foods can be found in tested instructions from official bodies.