Vacuum Brewing and the Vac Pot 2005/06/11
by Mike Nachaj

According to many, including myself, the vacuum coffee brewing method produces the best tasting filter coffee. The resulting brew is crystal clear with great purity of flavour and no bitterness added by the brewing process.

However, any faults in the coffee bean flavour also shown up with great clarity. So make sure to use good quality beans for this method.

A Little History
Once one of the most popular method of making coffee during the first half of the 20th century, the vacuum brewer, a.k.a. the "vac pot", almost completely disappeared from the North American marketplace by the end of the 1950s.

While other parts of the world continued to use vacuum brewers, most notably Europe and Japan, percolation, auto drip and instant coffee have replaced vacuum brewing altogether.

Vacuum brewed coffee was initially invented and introduced to France in the early 1840s. Mme Marie Fanny Amelne Massot of Lyons, who used the name of Mme Vassieux on her patents, is widely credited as the inventor of the vacuum brewer with the introduction of her reliable and commercially viable vacuum brewing device patented and manufactured in 1842. Although several devices and patented designs predate her invention, none really made it off the drawing board. Of note, some of Mme Vassieux original devices still exist today.

Throughout the latter half of the 1800s, various brewing devices based on the vacuum brewing method surfaced in Europe. Many were based on the Mme. Vassieux's designs, but a few, notably the side by side design by John Napier (called a Napierian) were truly remarkable contraptions.

These were somewhat dangerous devices, due to the very nature of the brewing process and the composition of the material used. Remember, these were the days before heatproof glass was perfected and the glass bubbles were prone to crack and explode when under pressure.

(For an interesting article covering some of the early vacuum brewing devices, check this out.)

Nevertheless, the vacuum brewer soon became very popular in North America and by the middle of the 20th century, companies like Silex, Sunbeam, Westinghouse, General Electric, and Cory had entire lines of vacuum brewers during this period.

But by the beginning of the 1950s, the vacuum brewing method began to lose favour in the convenience-obsessed Americas with the introduction of instant coffee and filter drip coffee makers. By the end of the decade, the vacuum brewer virtually vanished from the North American marketplace altogether.

In other parts of the world, vacuum brewing (also called siphon brewing) remained popular. In Japan for instance, vacuum brewing coffee is more popular than auto drip and probably accounts for the reason that there are several excellent Japanese and Taiwanese manufacturers of vac pots, including Tayli, Hario and Yama.

Today, the vacuum brewing method and vac pots are experiencing somewhat of a resurgence in interest, a quiet renaissance. A few companies offer remarkable good quality brewers, notably Cona (Britain UK), Bodum (Switzerland), and Hario (from Japan).

How the brewing method works
The vacuum brewer consists of an upper and a lower chamber that fit together with an air-tight seal fitted with a small filter. The lower chamber also contains a small siphon or tube that acts as a conduit between the two chambers. Incidentally, the lower chamber usually doubles as a decanter for the finished brew.

Coffee grounds are placed in the upper chamber while the water is pored into the lower.

When the lower chamber is heated to the boiling point, some of the water begins to change into water vapour (a gas) that gradually increases the relative pressure in the lower chamber. As more water vaporizes, the pressure increases to the point where there is sufficient pressure in the lower chamber to force the heated water up the siphon, through the filter and into the upper chamber containing the ground coffee.

This process continues until almost all of the water in the lower chamber is eventually forced up into the upper chamber where it is allowed to mix with the coffee grounds. The process usually takes from one to three minutes to complete.

The pressurized water vapour left in the lower chamber is also allowed to escape up thru the siphon and act as a heat source for the upper chamber brew and remains at the near ideal extraction temperature - between 185F and 200F.

Once all the water has made this pressure induced trip, the heat source is removed (or turned off). This allows the water vapour that is left in the lower chamber to gradually cool, (gas contracts) decreasing the relative pressure in the lower chamber and thus (in effect, creates a partial vacuum) allowing all of the brewed coffee to be drawn or sucked back down though the filter into the lower chamber. This suction occurs quite abruptly and is fun to watch!

The upper chamber is then removed and the freshly brewed coffee is poured out of the lower chamber which usually doubles as a handy-dandy decanter for the finished brew.

The beauty of this process is that the coffee is brewed by extended contact with water at a near perfect brewing temperature (185F to 200F) throughout the brewing process and the coffee brew is immediately separated from the grounds once the brewing is completed.

Question or comments? Send me an email at: mike@coffeebeatcafe.com

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Created by Mike Nachaj Last updated: Aug 1, 2004