A vacuum coffee maker brews

coffee Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...

using two chambers where

vapor pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

and

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

produce

. This type of coffee maker is also known as ''vac pot'', ''siphon'' or ''syphon coffee maker,'' and was invented by Loeff of

Berlin Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...

in the 1830s.

History and design

Since their invention, these devices have since been used in many parts of the world. 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. Vacuum coffee makers remain popular in some parts of Asia, including Japan and Taiwan. Design and composition of the vacuum coffee maker varies. The chamber material is

borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

, metal, or plastic, and the filter can be either a glass rod or a screen made of metal, cloth, paper, or nylon. The Napier Vacuum Machine by James Robert Napier, presented in 1840, was an early example of the vacuum brewing process. The

Bauhaus The Staatliches Bauhaus (), commonly known as the , was a German art school operational from 1919 to 1933 that combined Decorative arts, crafts and the fine arts.Oxford Dictionary of Art and Artists (Oxford: Oxford University Press, 4th edn., ...

interpretation of this device can be seen in

Gerhard Marcks Gerhard Marcks (18 February 1889 – 13 November 1981) was a German artist, known primarily as a sculptor, but who is also known for his drawings, woodcuts, lithographs and ceramics. Early life Marcks was born in Berlin, where, at the age of 18, ...

' coffee maker of 1925.

Balance siphon

An early variation of this principle is called a ''balance siphon'' or ''Belgian brewer''. 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 lowering pressure (creating a vacuum) and causing the brewed coffee to seep in.

Automated version

In 2022, Tiger Corporation released an automated coffee-maker based on the vacuum coffee maker principle, which was marketed as the ''Siphonysta''. The Siphonysta's heating is electrical. The chambers are made of plastic ("resin").

Brewing principle

A vacuum coffee maker operates as a

siphon A siphon (; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, abo ...

, where heating and cooling the lower vessel changes the

of water in the lower, first pushing the water up into the upper vessel, where the coffee is brewed, then allowing the brewed coffee to be strained as it is drawn back down into the lower vessel. Specifically, by heating (A) the water in the sealed lower vessel (B), the combination of its vapor pressure (the pressure exerted by the vapor component of a liquid) and the pressure from heating the air will exceed the ambient

standard atmospheric pressure The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level. History The ...

, causing some of it to boil, turning into water vapor. Since the density of water vapor is approximately that of liquid water, the mixture of air and water vapor in the lower vessel quickly expands as more liquid is boiled to vapor, increasing the pressure in the lower vessel. Water vapor pressure graph

Once the pressure in the lower vessel exceeds atmospheric pressure, the remaining water is pushed up through the siphon tube (C) into the upper vessel (D), where it remains, so long as the pressure difference between the upper and lower vessels is sufficient to support it, about . This pressure difference is maintained during brewing through the continuous heating of the lower vessel. Coffee grinds are added to the water in the upper chamber and coffee is brewed using the displaced water at slightly less than the boiling point, . When the coffee has finished steeping, the heat is removed and the pressure in the lower vessel decreases; when the combined force of gravity and atmospheric pressure overcomes the (decreased) pressure within the lower vessel, the brewed coffee is pulled into the lower vessel of the vacuum coffee maker, leaving the coffee grounds in the upper vessel. The iconic

Moka pot The moka pot is a stove-top or electric coffee maker that brews coffee by passing hot water driven by vapor pressure and Charles's law, heat-driven gas expansion through ground coffee. Named after the Yemeni city of Mocha, Yemen, Mocha, it was ...

coffee maker functions on the same principle but the water is forced up from the bottom chamber through the third middle chamber containing the coffee grounds to the top chamber which has an air gap to prevent the brewed coffee from returning downwards. (Additionally, because the water is forced up through packed grounds, the pressures are greater.) The prepared coffee is then poured off from the top.

References

External links

Vac Pot How-To pdf

{{coffee, nocat=1 Coffee preparation Vacuum Fluid dynamics Coffeeware