A very sophisticated procedure is to prepare a powder through freeze-drying. Since boiling or hot-air dehydration frequently impairs the chemical composition of a medicinal product, this method produces a very complete dehydration without much heat. Freeze-drying is frequently used in the commercial manufacture of antibiotics, vaccines and many nutritious and food products, since by using very low temperatures and high vacuum, it avoids overheating and perhaps deteriorating the organic product.

Under 0º C, water becomes solid (ice), which is a form in which food can be preserved. Under normal conditions, when water is defrosted by applying heat, it passes through the liquid state to end in the gaseous one (vaporization). There is, however, another form of extracting water from a frozen product, which is called sublimation. We call sublimation the direct passing from the solid into the gaseous state, without first going through the liquid state, in the case of water, from ice to steam. Freeze-drying is based on this principle, to quickly extract humidity from a product with a minimum of alteration of its molecular structure.

To attain this, the above-named principle is applied: the relationship between atmospheric pressure and vaporization. If a product contains frozen water and is exposed to a very low atmospheric pressure – a virtual vacuum – the water vaporizes directly. As it does not go through the liquid state, steam requires a minimum of space to get out. If the freezing process is done adequately, the structure of the organic matter is not altered. A further explanation is maybe required: when a food product is frozen, the water forms ice crystals, whose size is very small. This permits that when heat is applied in vacuum, the tiny crystals are sublimized, they convert directly to steam, without, by so doing, breaking the molecular structure, i.e. , without altering the composition of the organic matter.