The Vacuum Coffee Brewer
Perhaps the most elegantly scientific way to brew coffee in existence, vacuum coffee makers come in a variety of styles, able to operate via candle power, stove, or electricity if the correct model is chosen.
Based on the principle of vacuum extraction, the vacuum coffee brewer is renowned for producing amazing coffee in a very extravagant fashion. Through a clever two chambered design, the vacuum brewer looks more like a spaceship than a coffee maker, and requires a relatively high amount of care and preparation in its use. Largely a centerpiece for a collection, the regular use of a vacuum brewer will often result in breakage. Being made entirely of borosilica glass, they are not as resilient as a metal coffee pot, or an espresso machine. They do however make a phenomenally good coffee.
Due to the requirements for the formation of a siphon powered by vacuum, and the use and demonstration of the principle of convection within water the design of the vacuum brewer is inherently fragile. A glass bulb with a long glass stem is filled with coffee, placed on top of the glass brew pot and sealed in place with a large rubber bung. This contraption is then placed on a heat source and heated until the water in the base has boiled.
Through the process of boiling, the water will expand. As the water vaporizes, it fills the air cavity above the water, and being a sealed cavity, the pressure increases. This increase in pressure results in the forcing of water up the long glass stem into the bulb above. Once the water has boiled and a suitable pressure differential has built up between the outside world and the internal glass bulb, the heat is removed. The pot can then be placed on a cork mat. Care should be taken when moving the contraption, as it is full of nearly boiling water and can be very hot to the touch.
As the machine cools, the water in the top vessel, now mixed with ground coffee, is drawn back down the stem and into the base, through the equilibration of the pressure. The simple application of physics here is an elegant one that is characteristic of the European design tradition from which the device hails.
Once the water has been drawn back down into the base, with the coffee grounds left behind in the top, the top is removed and cleaned, then stored for safe keeping. Take extreme care when removing the top, as the bung can seal rather tightly. If there is a sudden jerking motion used to remove the bung and vessel the delicate glass stem that extends into the lower vessel can hit the walls, causing breakage. As these units are retro antiquities, they are not easy to replace, and breakage can be an expensive mistake.
Once the top is cleaned, and placed back in a safe place, the coffee pot can be taken to the table and the exquisitely tasty coffee poured into cups for all to enjoy. Again, take care, as the pot is hot and fragile.