With the rise of health-conscious consumption trends, freeze-dried fruit has gradually become a new favorite in the market. Many customers, when inquiring about freeze-drying equipment, often ask the same question: Does fruit need to be pre-treated before freeze drying? The answer is yes. Pre-treatment is a critical step that determines the quality of the final freeze-dried product.
Why is pre-treatment necessary before freeze-drying fruit?
Pre-treatment is recommended for almost all fruits prior to freeze drying. Its main purposes are to prevent browning, shorten drying time, protect nutrients, and enhance the quality of the final product. Different fruits require different pre-treatment methods due to their unique characteristics.
For fruits such as apples, bananas, and peaches, once cut, the enzyme polyphenol oxidase in the cells is exposed to air and oxidizes phenolic compounds, turning the fruit brown. Since freeze drying is a low-temperature process, it cannot deactivate this enzyme. Without proper pre-treatment, the finished product will appear dark and brown, making it unappealing in appearance.
For fruits with skins, such as blueberries, grapes, and cranberries, the dense waxy or cuticular layer on the surface severely hinders the sublimation of moisture. If left untreated, moisture cannot escape, leading to excessively long drying times, and the internal expansion of water during freezing may even cause the skin to burst, or the center may never fully dry.
Freeze drying is an energy-intensive and time-consuming process. Without pre-treatment, the uneven moisture distribution and high surface resistance of the fruit can extend drying time by 20%–50%. The pre-treated fruits can reduce drying time by 15%–20%; piercing treatment can shorten the drying time of blueberries by nearly half; and osmotic dehydration pre-treatment can improve the drying efficiency and crispness of strawberries. Clearly, pre-treatment is a core strategy for reducing costs and increasing efficiency.
What does the pre-treatment process involve?
1, Fruit Selection and Washing: Select fresh fruits free from disease and rot. Rinse thoroughly with clean water or wash with a 100–300 ppm sodium hypochlorite solution, then rinse again with water.
2, Trimming and Cutting: Peel, pit, and remove stems as needed, then cut into uniform slices according to specifications.
3, Color Protection and Soaking: Depending on the type of fruit, soak in an appropriate color-preserving solution or impregnation solution.
4, Draining and Tray Loading: Remove the fruit, drain excess surface moisture, and arrange evenly in a single layer on freeze-drying trays.
5, Pre-Freezing: Transfer the trays to a quick-freeze room and freeze at –30°C to –40°C until the core temperature of the fruit reaches the required level.
How KEMOLO Freeze Dryers support the pre-treatment process
In actual production, an efficient and smooth pre-treatment workflow relies heavily on well-matched supporting equipment. KEMOLO freeze dryers are designed with several features that integrate with the pre-treatment stage. KEMOLO freeze dryers come with a quick-freezing capability. When not used for freeze drying, they can serve as a freezer storage unit, enabling fast, large-scale pre-freezing of pre-treated fruits. This is far more efficient than conventional freezers and ensures the formation of fine, uniform ice crystals. Combined with the subsequent sublimation drying process, this yields high-quality finished products.
For KEMOLO's large-capacity equipment, pre-frozen batches can be easily and smoothly transferred to the drying chamber via rail and trolley systems. This significantly reduces manual labor and minimizes cold loss during transfer, making it particularly suitable for large-scale production.
