Vacuum-brewed coffee has been a favorite of connoisseurs since the late 1700s. Originally stacked vertically, a heated vessel of water forces boiling water into another vessel filled with ground coffee. As the lower vessel cools once the heating stops, vacuum pressure draws the brewed coffee through a filter into the other vessel. It's related to the basic mechanism used in many modern automated vacuum coffeemakers.
Borrowing from scientific experimentation, they also moved away from all-metal designs to ceramic and glass flasks designed for laboratory use. When coffee had a major 19th-century resurgence as a fashionable drink, European inventors came up with the idea of using two globes stacked vertically. Soon artisans from Belgium to Vienna were experimenting with creating beautifully crafted versions of the device, sometimes nicknamed "French balloons." These innovations allowed guests to watch the process as it happened. The most popular types were entirely self-contained and portable. This allowed coffee making to move from the kitchen or hearth to any room in the home.
Coffee historian Brian Harris notes that the first known fulcrum and counterweight design innovation came in 1844, when Viennese inventor Louis Gabet patented a device with a counterweight mechanism. It proved so popular it was often called a Gabet. Freiderich Liesche's Balancing Siphon Apparatus was patented in the United States in 1866 and is nearly identical to Gabet's counterweight design.
The addition of a counterweight both made it fun to watch and made it idiot-proof, as the model extinguished its own heating element once the water had boiled, fully automating the process and eliminating the possibility of burning the coffee. The process is the same vacuum brewing as before, but it took coffee-making from being utilitarian to being its own form of performance art.
This removable element remains stationary during brewing and is the vessel into which the ground coffee or loose tea goes. These flasks evolved from utilitarian lab-like flasks to elaborate etched and gilded shapes over the 19th century.
Vacuum flask and siphon
The innovation in the device primarily lies in the metallic vacuum flask design. Rather than pushing boiling water upward exclusively, the thin tube is designed as a siphon, with the end of the tube lower than the flask. Once the water is pushed up and over the uppermost curve of the siphon, Bernoulli's principle kicks in, and the remaining heated liquid travels out of the vacuum flask into the brewing flask. The end of the siphon tube has a metal filter head, and many models add a reusable cloth filter that gets tied around the metal siphon head for better filtering. The siphon tube has a rubber seal that keeps the vacuum flask airtight, and the filter head rests on the dry coffee or tea at the start of the process.
Once all the water has left the vacuum flask and the heat is removed, it begins to cool, forming suction which draws the brewed beverage back into the vacuum flask, where it is stored until ready to serve. To serve, simply unscrew a valve on the top of the flask to unseal the vacuum, then open the spigot to serve the hot and tasty beverage.
Though some early models used oil lamps or candles as heating sources, spirit lamps became the most popular choice because of the cleaner, hotter flame. Glass lamps with wicks could be filled with either ethanol spirits, or more commonly, surgical spirit (isopropyl alcohol). Better to save the drinkable spirits for other uses! Spirit lamps are a precursor to Bunsen burners, developed later in the century for better consistency and heat.
The entire apparatus would work just fine as a stationary piece of equipment, one that would look right at home in any lab of the day. By adding a fulcrum and counterweight for the vacuum flask, Gabet found the device could extinguish its own spirit lamp during the brewing process. He added a cap to the spirit lamp with its own counterweight. The cap is held open when the vacuum flask is in the lower position. As soon as the boiling water empties from the vacuum flask, the counterweight raises the vacuum flask. This in turn causes the spirit lamp cap to close and the cooling process to begin. As the brewed coffee fills the vacuum flask back up, the vacuum flask returns to its original position.
For a wonderfully detailed history of 19th-century coffeemaker design with copious diagrams, please visit Brian Harris' Historical Development of the Vacuum Coffee Pot.