What's the freezing phase in the freeze-drying process?

Freeze-dried foods taste almost the same as they did before with a minimal loss of taste or smell, moreover the freeze-dried process doesn't shrink or deform the substance therefore maintaining the structure of the substance.

Freeze-dried food cost considerably much more than wet food because the costs of the freeze-dried process and the expanses attached to it, including expansive machinery, energy expanses, etc.

The secondary drying phase purpose is to remove the remaining unfrozen water molecules. In this phase the temperature rises above 0, unlike the primary phase, in order to break any interactions that have formed between the water molecules and the frozen material.

During this process the pressure is lowered and head is inserted to the material in order to make the water sublime. In this slow process, about 95 percent of the water is sublimed. Furthermore the temperature during the primary drying phase is around -50 Celsius.

The pretreatment phase includes concentrating the product, adding components to increase stability. In many cases the decision to pretreat a product is based on the theoretical knowledge on the freeze-drying process. There are many method of pretreatment including freeze concentration, formulation to stabilize reactive products, formulation to Increase the surface area etc.

There are four main stages in the freeze-drying process, the pretreatment, the freezing, the primary drying and the secondary drying phases.

The freeze-drying process was first used in World War 2 in order to avoid spoiling serums sent from far way to treat wounded soldiers by freezing it and keeping the serum molecule composition in the optimal state.

Yes there is, in freeze-drying process they use a cold temperature and in dehydrated food they use warm temperature. In the freeze-frying process the fresh foods are frozen first then the moisture removed in a vacuum chamber and since the food remains frozen during the process, the food's cell structure don't change.