Vacuum Coffee Maker brews coffee using two chambers where vapor pressure and vacuum produce coffee which is clean, crisp, rich and smooth compared to other brewing methods. This type of coffee maker is also known as vac pot, siphon or syphon coffee maker and was invented by Loeff of Berlin in the 1830s. These devices have since been used for more than a century in many parts of the world. Design and composition of the vacuum coffee maker varies. The chamber material is pyrex, metal or plastic, and the filter can either be a glass rod, or a screen made of metal, cloth, paper or nylon. The Napier Vacuum Machine, presented in 1840, was an early example of this technique. While vacuum coffee makers generally were excessively complex for everyday use, they were prized for producing a clear brew, and were quite popular until the middle of the twentieth century.
The principle of a vacuum coffee maker is to heat water in the lower vessel of the brewer until expansion forces the contents through a narrow tube into an upper vessel containing the coffee grounds. When the lower vessel has more or less emptied itself and enough time has elapsed, the heat is removed and the resulting vacuum will draw the brewed coffee through a strainer back into the lower chamber from which it can be decanted. The device must usually be taken apart to pour out the coffee.
An early variation of this principle is called a balance siphon. This implementation has the two chambers arranged side by side on a balance-like device, with a counterweight attached to the heated chamber. Once the vapor has forced the hot water out, the counterweight activates a spring-loaded snuffer which smothers the flame and allows the initial chamber to cool down thus creating a vacuum and causing the brewed coffee to seep in.