What is freeze-drying?
Lyophilization (freeze-drying) is a process which extracts the water from foods and other products so that the foods or products remain stable and are easier to store at room temperature (ambiant air temperature).
Lyophilization is carried out using a simple principle of physics called sublimation. Sublimation is the transition of a substance from the solid to the vapour state, without first passing through an intermediate liquid phase. To extract water from foods, the process of lyophilization consists of:
- Freezing the food so that the water in the food become ice.
- Under a vacuum, sublimating the ice directly into water vapour.
- Drawing off the water vapour.
- nce the ice is sublimated, the foods are freeze-dried and can be removed from the machine.
Lyophilization has many advantages compared to other drying and preserving techniques.
- Lyophilization maintains food quality because the food remains at a temperature that is below the freezing-point during the process of sublimation.
- The use of lyophilization is particularly important when processing lactic bacteria, because these products are easily affected by heat.
- Foods which are lyophilized can usually be stored without refrigeration, which results in a significant reduction of storage and transportation costs.
- Lyophilization greatly reduces weight, and this makes the products easier to transport. For example, many foods contain as much as 90% water. These foods are 10 times lighter after lyophilization.
- Because they are porous, most freeze-dried foods can be easily rehydrated. Lyophilization does not significantly reduce volume, therefore water quickly regains its place in the molecular structure of the food.
The freeze-dryer unit we use is of our own design. Each dryer is composed of a large air-tight cylindrical reservoir, equipped with shelves to hold the trays of food to be freeze-dried. Access is through a large door, made of 6 cm thick acrylic, strong enough to resist the high pressure created when air is withdrawn from the freeze-drying unit to produce a vacuum needed for the process of sublimation.