The vacuum pot (also called the vac pot or siphon) method of brewing coffee is one of the oldest techniques still in use today—beautiful with its ornate design and sleek glassware. It revolutionized nineteenth-century coffeemaking in Europe after its invention in Germany in 1830. Much like the Chemex brewer, it fell out of favor in the mid-20th century for what came to be seen as unnecessary requirements in brewing: patience, practice and a steep learning curve. However, also like the Chemex, the vacuum pot is now enjoying something of a renaissance among fans of artisanal coffee.
While the vacuum pot was technically invented by Leoff of Berlin, it was a woman of Lyons, France known as Madame Vassieux who actually designed and patented the first commercially successful vacuum brewer in 1840. Her coffee brewer featured a glass “double balloon” held by a frame, featuring a metal crown and a serving spigot. It was a beautiful piece of work, but its design suggests that it may have been more suited to display than brewing, with too much emphasis on form over function.
What is certain is that there was room for improvement. The earliest siphons were tricky to use—1830s-era glass did not contain the heatproof qualities of today’s glass, and tended to crack or even explode from temperature changes. As a result, this version of the siphon eventually fell out of favor, leading to the development of the next significant advancement in vacuum pot technology— the balance brewer (or balancing siphon). This new variation placed the glass balloons next to (instead of atop) one another, and was designed to automatically extinguish the flame on the burner—a constant issue with the original vac pot—when the water chamber was empty by use of a spring-loaded lid.
By the time the vacuum pot reached America in 1894, it had undergone yet more shifts in design. The apparatus now featured a wider, flat bottom so it could rest on a burner, and a narrower upper globe for better balance. By 1915, the vac pots were being made from Pyrex, the Corning Glass Works’ newly introduced ovenproof glass, and were marketed under the name "Silex.” This basic 1915 design has been altered only slightly in its journey to today’s incarnation.
The Siphon In Action
Water sits in a bottom container; grounds are added to a top container. A siphon tube and filter connects the top and bottom containers. As the water heats, the resulting vapor forces it to rise up through the tube into the top chamber. The water mixes with the coffee grounds and extracts their flavor. The magic of the vac pot method is a trick of physics; the temperature at which sufficient water becomes vapor is the same temperature that makes for perfect coffee extraction. As the concoction cools, gravity sucks the freshly brewed coffee down into the lower chamber, leaving the dry grounds in the top chamber.
How To Brew With A Vacuum Pot