The commonly used methods for vegetable dehydration and drying are hot air drying and freezing vacuum drying. The freezing vacuum dehydration method is currently an advanced method for vegetable dehydration and drying, which not only preserves the original color, aroma, taste, and shape of fresh vegetables, but also has ideal rapid rehydration properties. So today we will talk about the processing process of frozen vacuum drying varieties such as fruits and vegetables:
1. Raw material selection: Leaf vegetables should not exceed 24 hours from harvesting to processing, and the yellow and rotten parts should be manually selected; Rootstock vegetables are manually selected for substandard products, decomposed parts, and graded.
2. Cleaning: Remove soil and other impurities from the surface of vegetables. To remove pesticide residues, 1.55% -1% hydrochloric acid solution or 0.05% -0.1% Potassium permanganate or 600mg/kg bleaching powder should be used to soak for several minutes for sterilization, and then rinse with clean water.
3. Peeling: Rootstock vegetables should be peeled. Chemical alkaline solution has a low loss rate of raw materials for peeling, but exported fruits and vegetables generally require manual or mechanical peeling. After peeling, it should be immediately put into clean water or color protection solution to prevent browning.
4. Slicing and shaping: Cut vegetables into certain shapes (granules, flakes), and vegetables that are prone to browning after slicing should be immersed in a color protection solution.
5. Hot water blanching: Generally, hot water blanching is used, and the water temperature varies with the variety of vegetables, usually above 100 ℃; The time varies from a few seconds to a few minutes. When blanching, salt, sugar, organic acids, and other substances can be added to the water to change the color of vegetables and increase their hardness.
6. Cooling: After blanching, it should be immediately cooled (water cooled or ice cooled), and the shorter the cooling time, the better.
7. Drying: After cooling, some water droplets will remain on the surface of vegetables, which is detrimental to freezing and can easily cause frozen vegetables to clump, which is not conducive to the next step of vacuum drying. The method generally adopts centrifugal drying.
8. Freeze: The drained material quickly freezes rapidly, with a freezing temperature generally below -30 ℃, preparing for the next step of vacuum drying.
9. Vacuum drying: the pre frozen vegetables are put into a vacuum container, and the pressure in the window is reduced to below the Triple point with the help of the vacuum system, and the heating system is used to supply heat to the materials, so that the moisture of the materials gradually evaporates until the drying ends.
10. Inspection and measurement: After freeze-drying, products should be immediately inspected, impurities and substandard products should be removed, and accurately weighed according to packaging requirements. They should be bagged and sealed.
11. Packaging: Vacuum packing with double plastic bags. Due to the oxidation and browning of the product, it can be packed with nitrogen and stored in an outer cardboard box.