Freeze Vacuum Drying Variety Processing
1. Selection of raw materials Leafy vegetables should not be processed for more than 24 hours from the harvest, and the yellow and rotten parts should be manually selected; the root vegetables should be manually selected and rotted, and graded.
2. Cleaning Remove soil and other impurities from the vegetable surface. In order to remove pesticide residues, it is generally necessary to sterilize with 1.55% - 1% hydrochloric acid solution or 0.05% - 0.1% potassium permanganate or 600 mg / kg bleaching powder for several minutes, and then rinse with purified water.
3, peeled root vegetables should be peeled. The loss rate of chemical lye peeling raw materials is low, but the export products generally require manual peeling or mechanical peeling. After peeling, they must be put into clear water or color protection liquid immediately to prevent browning.
4. Cutting and forming The vegetables are cut into certain shapes (granules and flakes), and the vegetables that are easy to brown after being cut should be immersed in the color protection liquid.
5, Blanching Generally use hot water blanching, the water temperature varies with vegetable varieties, generally more than 100 ° C; time is a few seconds to a few minutes. When blanching, add some salt, sugar, organic acid and other substances in the water to change the color and increase the hardness of the vegetables.
6. Cooling After the blanching is finished, it should be cooled immediately (water or ice water). The shorter the cooling time, the better.
7. Drain After cooling, some water droplets will remain on the surface of the vegetables, which is unfavorable for freezing. It is easy to make the frozen vegetables into pieces, which is not conducive to vacuum drying in the next step. The method generally uses centrifugal drying.
8. Freeze The material after draining is quickly frozen, and the freezing temperature is generally below -30 °C, which is ready for vacuum drying in the next step.
9. Vacuum drying The pre-frozen vegetables are placed in a vacuum container. The pressure in the window is lowered to below the triple point by means of a vacuum system, and the heating system supplies heat to the material, so that the moisture of the material gradually evaporates until it reaches the end of the moisture.
10. Separate inspection and measurement The products after freeze-drying should be inspected immediately, and impurities and other foreign products should be removed, and accurately weighed according to the packaging requirements, and put into the bag to be sealed.
11. Packaging Vacuum packaging with double plastic bags. Due to the oxidative browning of the product, it can be packed in nitrogen-filled packaging, and then placed in an outer carton for storage.