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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.
The vacuum evaporation treatment process consists of reducing the interior pressure of the evaporation chamber below atmospheric pressure. This reduces the boiling point of the liquid to be evaporated, thereby reducing or eliminating the need for heat in both the boiling and condensation processes.
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.
Evaporation is an essential part of the water cycle. The sun (solar energy) drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. Evaporation of water occurs when ...
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.
(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 increased dissolved solids act to increase the boiling point well beyond that of pure water. Seawater with a TDS of approximately 30 g/L exhibits a boiling point elevation of less than 1 K but saturated sodium chloride solution at 360 g/L has a boiling point elevation of about 7 K. This boiling point elevation is a challenge for vapor ...
Braising – combination cooking method using both moist and dry heat; typically the food is first seared at a high temperature and then finished in a covered pot with a variable amount of liquid, resulting in a particular flavour. Coddling – food is heated in water kept just below the boiling point.