1 / An answer to the problem of food preservation: Freeze-dried foods are those which keep the highest level of freshness; quality nutritional capacities; and a small volume to obtain quantities and varieties.

2 / The theory: Take a frozen food and dehydrate it under vacuum, changing it from a frozen state to that of perfectly dehydrated and preserved.

3 / The technique: In the vacuum technique used in lyophilization, water exists in solid form (ice) gas (vapor). The ice turns to vapor during the slow heating. Steam escapes from the product and increases the pressure inside the freeze-drying chamber. Without a way to contain this vapor, the vacuum pump would fill with water. In this case, the product could melt and it would then appear as air dried (shriveled, sagging and brown). To control the steam, panels refrigerated at -30 ° C are used. The vapor attracted by the cooler temperature of these panels condenses into ice on contact. This process reduces the amount of steam inside the chamber, so the vacuum remains at the same level throughout the process. The reheating of the chamber is crucial: if there is too much heat too quickly, there is release of steam. If the refrigeration system cannot condense it fast enough, the pressure rises and the product melts. The products are always freeze-dried from the outside to the inside. This means that it takes longer at the same temperature to dry the inside of the product. 80% of the drying time is used to dehydrate the center 20% of the product. Ex: it takes 14h to 16h to freeze-dry a whole strawberry!

4 / The most gentle method for the product: As the temperature remains low, the product remains intact, the sugars are not overheated and do not caramelize. This preserves taste and fragrance in the finished product. There is no reduction. A freeze-dried strawberry retains the same shape and volume. The water is gone leaving the fibers and solids in the product. The cell structure did not collapse allowing complete rehydration of the product. The downside: exposed to air, they absorb water, so the packaging must be waterproof. The advantage: it makes the use of preservatives and additives unnecessary. This method is used to treat plants that cannot be exposed to heat.