Sunday, September 27, 2009

Vacuum-brewed coffee

Vacuum coffee-makers are supposed to reveal the whole taste of coffee. We bought the vacuum coffee maker by Bodum, to our knowledge the most affordable.

Water in the closed lower chamber is heated. With heat and evaporation, the volume of the air increases in the lower chamber and pushes water through a tube to the upper chamber. Water brews the coffee in the upper chamber. When the temperature of the lower chamber decreases, the liquid is sucked back to the lower chamber and thus separated from the coffee grounds. (see on Wikipedia)

Our first try rendered an awfully diluted coffee. The tube plundges down to 1 cm above the bottom of the lower chamber. The Bodum vacuum coffee maker is designed for regular electric or gaz stove, so the bottom is flat, and a lot of water remains there when the air finds its way into the tube. Although the coffee ended up very diluted, its taste was promising.

We extended the tube with aluminium paper. Aluminium does not react with air, water or coffee, even at water boiling temperature, so it preserves the taste, drinkability and remains unaltered. Furthermore it transmits heat as well as water, so its presence does not alter heat exchanges. We rolled an aluminium sheet around the round handle of a wooden spoon. We introduced the spoon into the tube, leaving 5 cm of foil outside. We rolled another sheet around the tube to cover it from its base to the exterior end of the inside foil. Finally, we squeezed the aluminium into a steady 1 cm extension of the tube, while keeping the spoon handle inside the tube to avoid cloging it with foil. We somehow twisted the fixation of a spring designed to grasp the end of the tube in such a way that it handles a longer extension in a tighter diameter.

As a result, virtually all the water is sucked up into the upper chamber. More caution is required though, not to leave the coffee maker unattended on the stove. Without boiling water to evacuate heat, the glass could explode.

Vacuum-brewed coffee looks relatively transparent and lean, about like tea. However, its taste is rich like an excellent espresso. Some say vacuum brewing is the best way to prepare coffee, because water penetrates coffee just below boiling temperature. I tend to disagree. In my opinion, water penetrates coffee at a wide range of temperatures. It starts to be pushed up long before boiling. When air goes from the lower chamber through brewing coffee, the temperature of these bubbles can be above 100°C. Using French press shows that water at different temperatures extract different aroma. My opinion is that vacuum brewing extracts all the aroma with the wide range of temperatures and without boiling the coffee.