Year1
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In daily life, under one atmospheric pressure ( ), water boils at ℃. But the boiling point temperature of water is not static, it decreases (or increases) as the pressure decreases (or increases). For example, the boiling point temperature of water is ℃ when, has dropped to ℃ when, and has dropped to ℃ when. The lowering of the boiling point makes water easily vaporized. Since vapor water molecules have higher energy than liquid water molecules, water must absorb the latent heat of vaporization when it vaporizes, and its latent heat of vaporization increases as the boiling point decreases. According to this principle, the object to be processed can be placed in a closed vacuum box that can withstand a certain negative pressure and is evacuated by an appropriate vacuum system. As the vacuum degree in the vacuum box continues to increase, the boiling point temperature of water continues to decrease, and the water It becomes easy to vaporize. When water vaporizes, it can only absorb heat from the object to be processed, and the object to be processed can be quickly cooled.
2. Application of vacuum cooling
Since vacuum is everywhere, compared with traditional heat transfer methods (convection, conduction, radiation), vacuum cooling is not only fast and uniform, but also clean and hygienic, which is very suitable for Cooling of cooked food and pre-cooling of fruits and vegetables, etc.
Let us first take a look at the process flow of cooked food production
Raw material cleaning and processing (steaming, cooking, barbecue, etc.) Cooling and packaging of finished products
There is no doubt that cooked food must be cooled before packaging. Traditional cooling methods include indoor natural cooling, forced ventilation cooling, air-conditioning room cooling, cold storage cooling, etc. These cooling methods not only have long cooling times (several dozen hours), slow turnover, and occupy a large area, but also have uneven cooling, large temperature differences between the surface and the center, and more importantly, affect food hygiene and safety.
Nowadays, food processing generally adopts natural cooling method, which takes up a large area and takes a long time. Not only is it difficult to meet the requirements of rapid pre-cooling, it is also not suitable for industrial production. Some of them are directly placed in the cold storage for cooling, which is unreasonable and uneconomical, and cannot be cooled quickly and evenly.
When vacuum cooling is used to cool or pre-cool cooked foods, fruits and vegetables, bacteria in the air will inevitably stick to the food, causing secondary contamination of the food, especially between ℃, where bacteria are at high speed In the breeding area, quickly passing through this temperature range can greatly reduce bacterial breeding generations, and the bacterial load can be easily controlled, which will help improve food safety and extend the shelf life. This is of great significance for the implementation of food safety laws. It can be seen that samples used in the food processing industry also need an advanced method and equipment for rapid cooling.
Vacuum cooling is an ideal rapid cooling technology method that can meet the above requirements.
Therefore, the smaller the number of bacterial contamination before cooked food packaging, the better the antibacterial effect of modified atmosphere preservation packaging and the longer the shelf life. Generally, it is quickly cooled by vacuum and packaged with %%, %% controlled atmosphere preservation. The shelf life in supermarket refrigerated display cabinets can be up to days.
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