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Vacuum cooling is a rapid cooling technique for any porous product that has free water and uses the principle of evaporative cooling.Vacuum cooling is generally used for cooling food products that have a high water content and large porosities, due to its efficacy in losing water from both within and outside the products.
When the process is applied to food and the water is evaporated and removed, the food can be stored for long periods without spoiling. It is also used when boiling a substance at normal temperatures would chemically change the consistency of the product, such as egg whites coagulating when attempting to dehydrate the albumen into a powder.
Boiling is the method of cooking food in boiling water or other water-based liquids such as stock or milk. [13] Simmering is gentle boiling, while in poaching the cooking liquid moves but scarcely bubbles. [14] The boiling point of water is typically considered to be 100 °C (212 °F; 373 K), especially at sea level.
Because the cooling water, which is chemically treated fresh water, is at a temperature of 70–80 °C (158–176 °F), it would not be possible to flash off any water vapor unless the pressure in the heat exchanger vessel is dropped. A brine-air ejector venturi pump is then used to create a vacuum inside the vessel, achieving partial evaporation.
The liquid entering the circulation evaporator will boil in the separator, not on a heating surface, hence minimising fouling, whereas with plate evaporators, boiling will occur on a heating surface. [15] It is for this reason that circulation evaporators are preferred for liquids with a higher tendency to foul.
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(By contrast, in the boiling pot example, the water vapor pushes the air out of the pot before it can reach the lid.) At a typical pressure of 10 −4 Pa, a 0.4-nm particle has a mean free path of 60 m. Hot objects in the evaporation chamber, such as heating filaments, produce unwanted vapors that limit the quality of the vacuum.
The oil layer is the method of heat transfer between the burner and the food. Water vapor is a critical component of how pan frying works. Raw meat products contain up to 73% water. [4] The meat is cooked by the evaporation of this water. When the water is vaporized it leaves the meat through pores in the surface of the meat.