Culinary Technique - Freeze drying

Freeze-drying, also known as lyophilisation, is a sophisticated industrial preservation technique used in the food sector. The process begins by freezing the product at extremely low temperatures, typically between -30 and -80 °C. The pressure is then reduced to create a vacuum environment. As the temperature is gradually increased, the frozen water inside the product sublimates — meaning the ice turns directly into vapour without becoming liquid. This removes virtually all moisture from the food.

The result is a dried product that is significantly lighter and smaller in volume, while largely retaining its original shape, vitamins and flavour. Because of the absence of moisture, the development of micro-organisms is prevented, considerably extending shelf life.

Although instant coffee is the most familiar example, freeze-drying is widely applied to vegetables, fruits, herbs and even edible flowers. It is particularly useful for herb and vegetable blends used in soups, as well as for various fruit preparations.

Despite its many advantages — including preserved taste, reduced weight and extended storage life — freeze-drying does alter the product’s structure, often making it more fragile or porous. In addition, the process remains technically complex and relatively costly compared to other preservation methods.

Technique:

Freeze drying is a sophisticated drying technique. The food is first frozen at a very low temperature, between -30 and -80 °C. Pressure is lowered in the freezer, which produces a vacuum. Then the temperature is gradually increased, more or less slowly depending on the type of product being freeze-dried, and the ice becomes vapour. This ensures that all the water in the product is extracted. One obtains a dried product that is smaller and lighter, but has kept its shape, vitamins and taste. The advantage is that it takes up less room, weighs less and keeps for a long time. This technique is used in particular for certain herb or vegetable mixes for soups, as well as for various fruits. Instant coffee is a familiar example of freeze-drying.