Dehydration is one of the oldest food preservation methods on earth. Take out the water, and micro-organisms cannot spoil the food. Everything else — flavour, colour, nutrients — depends on how the water is removed.

Sun-drying

The oldest method. Fruits and vegetables are laid on trays under direct sunlight for days. Cheap, energy-free, and traditional. Downsides: exposure to dust and insects, uneven drying, and loss of heat-sensitive vitamins like vitamin C.

Air (convection) drying

Warm, moving air passes over food in a controlled chamber (typically 40–65°C). Faster and cleaner than sun-drying. Most commercial dried fruits, mushrooms and vegetables are produced this way. Colour, texture and nutrients are better preserved than sun-drying.

Vacuum drying

Air is removed, so water boils at a much lower temperature. Gentler on colour and flavour than plain hot-air drying.

Freeze drying

The gold standard. Food is frozen solid, then placed in a vacuum where the ice sublimates directly to vapour — skipping the liquid phase entirely. Because temperatures stay below 0°C, virtually all colour, aroma, nutrients and shape are preserved. Freeze-dried strawberries, coffee and instant meals for astronauts all use this method.

Spray drying

A liquid is sprayed as fine mist into a chamber of hot air. Water evaporates almost instantly, leaving a fine powder. Used for milk powder, instant coffee, egg powder and many beverage mixes.

Which is “best”?

It depends on the goal. Freeze drying preserves the most nutrients and structure but is expensive. Sun and air drying are cheaper and give the classic “dried fruit” chewy texture that many people prefer.