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Vacuum pre-cooling versus traditional pre-cooling methods:
1. Differential pressure pre-cooling:
The suction effect of the pressure differential fan can form a pressure difference on both sides of the product packaging that needs to be pre-cooled, so the product packaging needs to be set up with ventilation holes. Under the action of pressure difference, the cold air flows into the ventilation holes to directly exchange heat with the surface of the product, which significantly increases the heat exchange area and air flow rate and enables the product to be cooled quickly and evenly. The pressure difference pre-cooling makes the product distribution more reasonable, the cooling is even, the pre-cooling time is about 3~4h, compared with the traditional pre-cooling method greatly shorten the pre-cooling week, however, the pressure difference pre-cooling investment and operation cost is higher, the palletizing and stacking waste time, the labour cost is higher.
2. cold water pre-cooling:
Cold water pre-cooling is generally the product diffuse soak in cold water, or cold water to the product spray clinic water for cooling. A better design of the spray clinic water equipment can also get faster pre-cooling speed, and the day will not cause water loss dry consumption. However, water pre-cooling cannot be used for fruits and vegetables that are prone to spoilage when exposed to water. The water used for pre-cooling is recycled water, which can easily contaminate the product and cause secondary contamination if preservatives are added. This will become a fatal flaw in the constant pursuit of green and safe food.
3. Forced ventilation pre-cooling:
Forced ventilation pre-cooling is a more traditional pre-cooling method. Directly place the product in the cold storage, the use of ventilation equipment, promote cold air through convection to take away the heat. This pre-cooling method of cooling uniformity is poor, pre-cooling time is very long, generally applicable to the products picked from the field without packaging treatment and not easy to corruption, storage time is long. Forced ventilation pre-cooling is more widely used in China and is less expensive. The initial investment is the lowest in several pre-cooling methods, but the pre-cooling time of the product after packaging has increased significantly, and can even reach as long as 2 days.
4. vacuum pre-cooling:
Vacuum pre-cooling is currently the fastest way to cool down pre-cooling, most fruits and vegetables as well as cooked food can be used. Fruits and vegetables are generally pre-cooled to a suitable storage temperature of 0.5 to 5°C in 20 to 30 minutes. Cooked foods can be pre-cooled from a high temperature of 90-100°C to room temperature of 15-20°C in about 10 minutes. Vacuum pre-cooling uses a vacuum pump to remove gas from the vacuum chamber, which reduces the pressure in the chamber and speeds up the evaporation of water from the surface of the product, thus taking away most of the heat to achieve rapid cooling. Vacuum cooling can inhibit the growth of bacteria, cooling uniformity, the minimum temperature difference between inside and outside the product in a short period of time, very conducive to temperature control.