Monday, January 3, 2011

The Vacuum Coffee Makers

The parts

Though it is a kitchen appliance, a vacuum coffee maker could easily be mistaken to a chemistry lab equipment. It consists of two overlapped glass bowls (containers), that communicate through a syphon tube; the upper container has at its bottom a filter(cloth, metal, glass, or plastic and paper mixtures).

The operating principle

The water is placed in the bottom container, the ground coffee in the upper one, above the filter. The equipment comes placed over a stove top. When the water is heated enough, it turns to vapors, that tend to expand and pass through the syphon tube in the upper chamber. The process lasts about three minutes - a complete brewing cycle. When the heat source is removed, the vapors cool off, they turn back to liquid and their volume contracts, creating a vacuum that forces the liquid back to the bottom container, through the filter.

Types of Vacuum Coffee makers

  • the two globe type - dates back in the 1920's and the first model was provided by the American company, Silex;
  • the balance type (the first automatic device) - works on the same principle as the two globe brewer, only with the two chambers placed side by side;
  • the Napier (or the one way) vacuum brewer - is a less common device that changes a bit the brewing process: most of the water is placed in the same chamber with the ground coffee, and only a small quantity in the other-side bowl. When heat is applied, the water in the side-bowl expands more quickly through the syphon tube, and agitates the coffee and water mixture; when heat is removed the vacuum is formed and coffee pushed through the syphon into the side-bowl;
  • the modern-automatic type - the first model provided by Farberware had the bottom made of a copper and chrome alloy and kept the glass top; it added a heating element tied to a primitive thermostat, that would suppress the heat when the brewing cycle was over; however, the cycle repeated as the installation cooled off,over and over, until it was unplugged; the first really modern automatic device was put up by Sunbeam.


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