Freeze-drying is a technique for the preservation of food that is based on the drying of certain compounds by means of the sublimation of the water contained in them.
A lyophilizer is the apparatus used to carry out lyophilization. It consists of the following parts: dry chamber or lyophilization chamber: it is the place where the substance to be lyophilized is placed, condenser with a refrigeration circuit: it communicates with the dry chamber and it is where the vapor that is produced in the sublimation is condensed and finally a vacuum system.
Through this technique, the physicochemical structure of the product is not altered and it allows its conservation without a cold chain, because its low percentage of humidity allows it to obtain great microbiological stability.
Freeze drying allows the extraction of 95% of the water contained in a food, which in turn translates into a great benefit in relation to the cost of transport, since it allows to load a greater quantity of merchandise without resorting to the cold chain. At the end of the freeze-drying process, the food becomes a rigid structure that preserves its shape and volume, but with reduced weight, maintaining its nutritional and organoleptic characteristics. By rehydrating it, they recover the original texture, aroma and flavor.
Operation of a food freeze dryer
You should know that to introduce any material into the lyophilizer, it first needs to be frozen, in order to maintain its molecular structure. To achieve this, a freezer capable of reaching sub-zero temperatures is used. The frozen material is introduced into the lyophilizer, where there is a vacuum pressure, thanks to the action of a vacuum pump, which allows it to function correctly. Due to the vacuum, 95% of the water present in the sample is sublimated. In this way, the product dries without the need to use temperatures above room temperature.
The heat contained in the lyophilizer provides the necessary energy to the water to turn into a gaseous state, accelerating the process. And the gas that remains loose is condensed at low temperatures, returning to a solid state again.
Freeze drying process
Food freeze drying involves four main stages:
- Primary desiccation
- Secondary desiccation
Benefits of lyophilization compared to other techniques:
- You get products that can be regenerated very quickly.
- The shape and characteristics of the final product are essentially the original ones.
- It is an ideal process for drying thermolabile substances.
- Oxidizable constituents are protected.
- The final moisture content is very low.