What İs Freeze Drying?
Freeze-drying, sometimes called lyophilization, is a promising preservation method. In freeze drying, a product is first frozen, then the pressure is reduced and the ice is removed by sublimation. Sublimation is the conversion of a substance from a solid to a gas without first being liquefied. Unlike other preservation methods that use heat to evaporate the water, freeze drying removes the water in the form of ice.
The lower temperature provides a higher quality end product. The product not only retains its original shape, but the process is also very sensitive to vitamins. Therefore, freeze drying is mainly used in biomedicine and food processing, because nutrients and active ingredients are preserved particularly well.
Freeze Drying Stages
1- Freezer
There are several methods for freezing the product. Freezing can be done in a cold bath, in the refrigerator, or directly on a shelf in a freeze dryer. Cooling the material below its triple point allows the product to sublimate rather than dissolve. Thus, the shape of the product is preserved in the best possible way.
The large ice crystals formed by slow freezing are the easiest to freeze-dry. However, if the crystals are too large, they can destroy the cell walls of the product, resulting in a lower quality end product. To avoid this, the freezing process is carried out as quickly as possible.
2- Freeze-Drying Through Drying Cycles
The second stage of freeze drying is called primary drying (sublimation), where the pressure is reduced (a vacuum is created) and heat is applied to the product to allow the water to sublimate. Vacuum promotes sublimation. The condenser provides a surface for the water vapor, in the case of the ADK freeze dryer, the vacuum chamber wall is the condenser to which the water vapor adheres and solidifies in the form of ice. The condenser also protects the vacuum pump from water vapor. Too much heat at the same time can affect the structure and shape of the material.
This is followed by other stages of freeze drying, which is secondary drying (adsorption) in which ionically bound water molecules are removed. By increasing the temperature in small steps more than the primary drying phase, the bonds between the material and the water molecules are broken. These drying stages can take place at intervals of, for example, 10°C and can be flexibly adjusted using the automation control of the freeze dryer. Freeze-dried materials retain a porous structure. After the freeze-drying process is complete, the vacuum can be broken before the material is hermetically sealed. Thanks to this process, most materials can be dried to 1-5% residual moisture.
Time of Freeze Drying
The freeze-drying time is crucial to the use of a freeze-dryer. However, freeze-drying times vary greatly between different materials, as the water content is the main cause of the differences. But other factors also play a role. Oranges and tangerines, for example, have extremely waterproof skin and store water very well.
In this case, slicing the fruit is crucial - smaller pieces are easier to freeze-dry. Thick-skinned fruits are generally also good at storing water, for example blueberries. On the other hand, it is very easy to freeze-dry strawberries.
The table below shows the drying times for approximate medium-sized items. 10 mm at end temperature of 25°C, 40°C and 60°C.
The higher the temperature, the faster the drying process, but the slower drying preserves more vitamins and better structure. Therefore, temperatures and drying cycles must be adjusted individually depending on the desired quality of the final product, which can be guaranteed by the flexible user interface of the ADK freeze dryer.
Adk project continues to provide services in all processes required in FREEZE DRY, LYOPHILIZATION, FREEZE DRYING facilities.
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- Cold storage design and contracting,
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