Vacuum evaporation

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Vacuum evaporation is the process of causing the pressure in a container to fall until water's boiling point has been lowered to room temperature. When the process is applied to food and the water is evaporated and removed, the food can be stored for long periods of time without spoiling.

This process was invented by Henri Nestlé in 1866, of Nestlé Chocolate fame,^{[citation needed]} although the Shakers were already using a vacuum pan earlier than that (see condensed milk).

This process is used industrially to make such food products as evaporated milk for milk chocolate, tomato paste for ketchup and liquid malt extract or dry malt extract for beer.

Vacuum evaporation is also a form of physical vapor deposition used in the semiconductor, microelectronics, and optical industries and in this context is a process of depositing thin films of material onto surfaces. Such a technique consists of pumping a vacuum chamber to pressures of less than 10 ^{- 5} torr and heating a material to produce a flux of vapor in order to deposit the material onto a surface. The material to be vaporized is typically heated until its vapor pressure is high enough to produce a flux of several Angstroms per second by using an electrically resistive heater or bombardment by a high voltage beam.

See also

• Freeze drying
• Ultrasonic spray deposition
• Vacuum deposition

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