Food Freeze Drying
Freeze drying is a very gentle dehydration process used for preservation of high quality foods, fruits, vegetables, dairy, nutrition and probiotics.
Freeze drying is a very gentle dehydration process used for preservation of high quality foods. Begins in 1950s, food freeze drying industry now is rapidly growth. The global freeze-dried food market is growing at 7.4% a year. Fruits comprise the largest portion of the global freeze dried food market.
Freeze drying is the process by which the water is crystallized at low temperature and is removed by sublimation. Sublimation is the direct transition of water from solid state to gaseous state, without pass through liquid state (melting). No liquid water involves in freeze drying means no high temperature is needed to boil/vaporize the water. So, freeze drying is a low temperature dehydrate way.
There are three stages in the process: Freezing, Sublimation drying (Primary drying), and desorption drying (Secondary drying).
The freezing phase is the most critical in the entire freeze-drying process. It is the base of a success freeze drying. It is important to freeze foods completely to avoid water boiling during vacuum drying. In addition, rapid freeze food can avoid large ice crystals form, which may deteriorate the final product quality.
During the primary drying phase, the pressure is lowered through the application of a high vacuum, and heat is applied to provide the energy needed for the ice to sublime. This initial drying phase removes about 95% of the water present in the food. This step can take several hours to days.
Secondary drying phase is to remove unfrozen water molecules remaining after primary drying. During this phase, the temperature is raised higher than in the primary drying phase in order to vaporize the water molecules. Pressure is frequently lowered during this phase, but not in all cases.
The final freeze-dried food typically contains between 1% and 5% moisture. The ultra low moisture contain makes they can be stored in room temperature more than 2 years and up to 25 years.
Freeze dried foods with superior quality as compared with other dehydration methods. The high quality is due to the absence of a liquid phase, as well as the low temperature of the process. Freeze-drying preserves flavor, color, and appearance, while minimizing thermal damage to heat-sensitive nutrients. In addition, the texture is well preserved due to the process occurring in solid state. Freeze-dried products are typically crisper and have rehydration ratios four to six times higher than conventional air dried foods. Other key benefits of freeze-drying include the high recovery of volatiles, retention of structure and surface area, high yield, long shelf life, and reduced weight for storage, shipping, and handling.
Freeze drying now used a lot in coffee, fruit, vegetables, herbs, food flavorings, fish, seafood, eggs, and dairy industries. Individual food types can be freeze-dried, as can dishes with multiple ingredients, such as stews or soups. As a result, freeze-dried foods can be used for backpacking, camping, military rations, survival food storage, and space exploration. Generally, larger-sized foods (such as fruit or meat) need to be cut into smaller pieces prior to freeze-drying. Thermally sensitive materials, such as fruits, are good candidates for freeze-drying. These have become popular as snacks and ingredients in other foods, such as breakfast cereals. Meat and seafood require cooking before freeze-drying.