Freeze drying, also known as lyphilization, is a method of dehydrating food for preservation and storage. During freeze drying, food products are dehydrated in a frozen state, preserving taste and nutrition as well as preventing microbial growth from occurring. Freeze drying preserves both raw and cooked foods. As with most methods of food preservation, there are advantages and disadvantages to freeze drying. Depending on your priorities and goals, you can decide if freeze drying is the right choice for your food products.
During the freeze drying process, food products are flash frozen and then placed in a large vacuum chamber. Inside the vacuum chamber, temperatures reach as low as negative 10 degrees C. Minimal heat is then applied, causing ice in the food to evaporate without ever reverting back to liquid form. All moisture is thereby removed from the food product. Freeze dried foods quickly reconstitute with the application of warm water, regaining their original texture and appearance. The flavour and aroma of the food is also not affected.
One of the main disadvantages of freeze drying is the expense. The equipment need for the freeze drying process, which requires very low temperatures, can be quite costly. "It is usually carried out under vacuum, at absolute pressures that readily permit ice to change directly from solid to vapour," according to The National Sustainable Agriculture Information Service.
Not all foods are able to withstand the freeze drying process. Freeze drying is only cost-effective for select foods like fruits and meats. Even foods that are able to endure the process can become damaged during the initial freezing. Freeze drying will preserve the colour properties of foods, although this is not true in every case. Certain foods such as carrots need to be pretreated so they are not subject to colour loss.
Storage problems can be another disadvantage to freeze drying foods. During the freeze drying process, foods keep their original shape and size, meaning that they may require extra storage space compared to other preserved foods. If freeze dried foods are not stored correctly, or if they are subject to humidity, they will deteriorate very rapidly. Freeze dried foods require storage in airtight, moisture-tight containers such as cans or bags. These products are also very frail, crumbling easily if not handled and stored with care.