There are two types of dehydration drying methods: natural drying and artificial dehydration. Artificial dehydration includes hot air drying, microwave drying, puffing drying, infrared and far infrared drying, vacuum drying, etc. At present, the application of vegetable dehydration is more hot air drying dehydration and freeze vacuum drying dehydration. The freeze vacuum dehydration method is currently an advanced vegetable dehydration drying method. The product can retain the original color, aroma, taste, and texture of fresh vegetables. Shape, but also has the ideal rapid rehydration. The technological process and method of hot air drying dehydrated vegetables and freeze vacuum dried dehydrated vegetables are introduced as follows.
Processing flow and method of hot air drying varieties
1. Selection of raw materials Choose vegetables with rich meat quality. Before dehydration, you should strictly select the best and remove the bad ones, and remove the parts with diseases and insect pests, rotten and shriveled. Eighty percent of the maturity is appropriate, and those that are overripe or underripe should also be picked out. Except melons with seeds removed, other types of vegetables can be washed with clean water, and then placed in a cool place to dry, but should not be exposed to the sun.
2. Cutting and blanching The cleaned raw materials are cut into slices, shreds, strips and other shapes according to product requirements. When pre-cooking, it varies with different raw materials. The easy-to-cooked ones are boiled in boiling water, and the hard-to-cooked ones are boiled in boiling water for a while. The general blanching time is 2 to 4 minutes. Leafy vegetables are best not blanched.
3. Cooling and draining The pre-cooked vegetables should be cooled immediately (generally by showering with cold water) so that they can quickly drop to room temperature. After cooling, in order to shorten the drying time, you can use a centrifuge to shake the water, or you can use a simple manual method to drain it. After the water is drained, you can spread it out and let it cool for a while, so that you can put it on a plate and bake it.
4. Drying Different temperature, time, color and moisture content during drying should be determined according to different varieties. Drying is generally carried out in a drying room. There are roughly three types of drying rooms: the first is a simple drying room, which uses countercurrent blast drying; the second is a drying room with two layers of double tunnels and a combination of forward and countercurrent; The drying temperature ranges from 65°C to 85°C, drying at different temperatures and gradually cooling down. When using the first and second drying rooms, spread the vegetables evenly in the tray, then put them on the pre-set drying rack, keep the room temperature at about 50°C, and keep turning them at the same time to speed up the drying. The time is about 5 hours.
5. Sorting and packaging After the dehydrated vegetables have been inspected to meet the requirements of the Food Sanitation Law, they can be packed in plastic bags, sealed, packed, and then put on the market.
Freeze vacuum drying varieties processing flow
1. Selection of raw materials Leafy vegetables should not exceed 24 hours from harvesting to processing. Manually select the yellow and rotten parts; root vegetables manually select out-of-grade and rotten parts and grade them.
2. Cleaning Remove soil and other impurities on the surface of vegetables. In order to remove pesticide residues, it is generally necessary to soak in 1.55%-1% hydrochloric acid solution or 0.05%-0.1% potassium permanganate or 600 mg/kg bleaching powder for several minutes to sterilize, and then rinse with clean water.
3. Peeling Root vegetables should be peeled. Chemical lye peeling has a low loss rate of raw materials, but export products generally require manual peeling or mechanical peeling. After peeling, it must be put into clean water or color protection solution immediately to prevent browning.
4. Slicing and shaping Cut the vegetables into certain shapes (grains, flakes), and the vegetables that are easy to brown after cutting should be immersed in the color protection solution.
5. Blanching Generally, hot water is used for blanching, and the water temperature varies with the variety of vegetables, generally above 100°C; the time ranges from a few seconds to a few minutes. When blanching, some salt, sugar, organic acid and other substances can be added to the water to change the color and increase the hardness of the vegetables.
6. Cooling After blanching, it should be cooled immediately (water cooling or ice water cooling). The shorter the cooling time, the better.
7. Drain. After cooling, some water droplets will remain on the surface of the vegetables, which is not good for freezing. It is easy to make the frozen vegetables agglomerate, which is not conducive to the next step of vacuum drying. The method generally adopts the centrifugal drying type.
8. Freezing The drained material is quickly frozen, and the freezing temperature is generally below -30°C, which is ready for the next step of vacuum drying.
9. Vacuum drying Put the pre-frozen vegetables into the vacuum container and use the vacuum system to reduce the pressure in the window below the triple point, and the heating system supplies heat to the material, so that the material moisture gradually evaporates until it is dried to the end of the moisture.
10. Sorting and measuring The freeze-dried products should be sorted immediately to remove impurities and off-quality products, and accurately weighed according to the packaging requirements, and put into bags to be sealed.
11. Packaging Vacuum packaging in double-layer plastic bags. Due to the oxidative browning of the product, it can be packed with nitrogen, and put into an outer carton for storage after packing. Vegetable dehydrator production process