As early as the 15th century, it was known what freeze-drying is. This method was already used by the Incas – they kept their crops in the cold environment of the Machu Picchu highlands, where they froze and the water evaporated slowly due to the sparse and low air pressure of the highlands.
Freeze-drying or lyophilization. During freeze-drying, the berries and fruits are dried under vacuum (0.05 ATM) and very cold (up to -80 ° C). Depending on the moisture content, the temperature is slowly raised. The process can take several hours (even days) until the fruits gradually dry out. The process takes so long that the absorption of the liquid does not cause overheating, which can change the composition and structure.
During this process, the water in the berries goes to the ice and the vacuum system removes the ice from the fruit and converts it into steam without going through a liquid state. This phenomenon is called sublimation – the conversion of water from a solid to a gaseous form. It is for this reason that berries, fruits, vegetables and herbs do not change their shape, volume or color after freeze-drying. The natural taste, aroma, appearance and nutritional value (including vitamins) of fruits and herbs are also preserved.
As there is no more diluting water in the plants, only the taste of very sour and sweet berries and fruits has slightly intensified. The textures of all freeze-dried fruits become specific – airy and crunchy. By using this method, cell breakdown is minimal and the nutritional value of the food is preserved. Since the plants are dried to below 39 ° C, the fruits dried in this way are also called raw food.
Virtually all the water is removed from the fruit (depending on the plant and its size, about 1-5% of water can remain in the plant) – this also prevents the growth of bacteria and the nutrients can be stored for up to 20 years. The actual shelf life depends on the type of packaging, storage temperature and plant. Thus, there is no need to add preservatives or other additives to the product.
Because virtually all of the liquid has been removed from the freeze-dried food, the result is an extremely light food that weighs up to 90% less than fresh fruit. Therefore, such foods are perfect for hikers and mountaineers, for example, to take with them when they have to carry their own food supplies.
After the nutrients have dried to be porous and sponge-like, when they come into contact with water (liquid), they quickly absorb the liquid and recover almost completely and acquire the original properties.
Freeze-drying makes it possible to obtain the best quality products compared to the use of known drying methods.
Read about other storage methods here.
Freeze-drying technology is not only used to dry nutrients. This technology is also used, for example, to dry books and works of art that have been damaged by water.
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