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How does a Vacuum Coffee Maker Work?

By Garry Crystal
Updated Feb 04, 2024
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A vacuum coffee maker uses a process that cooks up coffee with an extremely strong flavor. That said, the flavor and strength of coffee is usually determined by how much coffee you use. While a lot of coffee makers destroy the flavor by failing to mix the components properly, a vacuum one is said to mix the water and the coffee perfectly.

A vacuum coffee maker consists of two mixing units, usually made of glass: an upper and a lower pot. The upper pot sits directly on top of the lower one, and they are sealed together with a stopper. A filter and tube are attached to the upper pot, and the tube hangs between the two pots.

This type of coffee maker uses ground coffee, usually of a coarse texture. The coffee grounds are added to the upper bowl. How much coffee you use depends on how strong a taste you prefer. One rounded tablespoon of coffee per cup of water will usually suffice if you like your coffee extra strong.

Next, the lower bowl is filled with water and placed over a heating element until it is almost at boiling point. Then, the upper pot can be placed onto the lower pot and sealed. Increasing pressure in the lower pot caused by boiling will make the water rise through the hanging tube and flow into the upper pot, and the brewing process will begin.

The water and coffee should be left to mix for around three or four minutes. The brewing time depends on how strong you like the flavor of your coffee. If you are a beginner at using a vacuum coffee maker, experimentation with timescales should eventually produce the desired results.

Remove the coffee maker from the heating element, and the cooling process will cause a vacuum in the lower pot. The water will filter back down into the lower pot. As the water filters down, most of the coffee grounds will be filtered out, although some may remain in the water.

You can now separate the two pots, and the lower pot can be used to serve the coffee. The greatest benefit to taste when using a vacuum coffee maker is that the temperature used is perfect for brewing coffee. Unlike in some other brewing processes, such as the drip-brew technique, none of the oils and flavors of the coffee are lost.

The vacuum coffee maker is considered superior to many other coffee brewing processes. The famous Santos vacuum coffee maker, designed by Swedish designer Kass Kleeson, is a staple in nearly every Scandinavian home. The explosion in coffee in the past decade has returned this nearly forgotten process to popularity.

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Discussion Comments

By anon32132 — On May 16, 2009

To anon5304: Even at 145F the water would have a higher vapor pressure than when it was cold. In a sealed container this can provide more than enough head pressure to push a water column up a paltry few inches into the upper chamber.

By anon20290 — On Oct 28, 2008

To Garry, anon2080, and anon5304,

A few points:

1) it is mostly pressure from water vapor that forces the water up to the top pot. It is not due to the expansion of a heated gas (air or water vapor) but the conversion of liquid water to water vapor. The same amount of water takes up a much greater volume as a vapor than it does as a liquid. It is the need for all that extra space that cause the pressure.

2) It is best to *not* attach the top to the bottom until the water is almost at the point of boiling. Otherwise cooler water can be forced up the tube. You want the near-boiling temperature for proper extraction. As a related point: It is often recommended to use preheated water to shorten the overall process when using vacuum brewers that rely on small flames to heat the water.

3) You control the brewing time by leaving the heat source on the lower pot (keeping up the pressure) while the water and coffee mix in the top. The mixing is enhanced by the bubbling action of water vapor coming up the tube. This gives you just a much control over the process as you have with French Press and the resulting product has many fewer grounds in it making for a much cleaner brew.

4) Do not use a course grind. Ideally, all brewing methods would use a fairly fine grind for better extraction. This must be compromised with other brewing methods. Drip can't use too fine a grind or it slows down the drip process, perhaps even causing an overflow. French Press has trouble with grinds in the final result even with course grinds. Vacuum brewers usually have a better filter system since they can use the power of the vacuum to suck the coffee through the grinds and filter. All meaning that there are fewer compromises in the vacuum process. Kind of like the espresso process.

By anon5304 — On Nov 20, 2007

My vacuum coffee maker makes really good coffee, but I have found that the cold water in the bottom results in water entering the top chamber at about 145F. That's right, only 145. I measured with two separate thermometers, both reading the same. I can't explain it.

If you love coffee, you probably already know this: stick with the french press, it gives you more control and is a snap to clean. I still use the vacuum when I want to make more coffee, mild coffees (islands and centrals), or when I want to impress someone.

By anon2080 — On Jun 27, 2007

I was first introduced to vacuum coffee 35 years ago when I purchased an old Cory vacuum unit at an antique store. I find it the preferred way to make coffee, but I have to disagree with you on the procedure that you use to make vacuum coffee.

Rather than heating the water before putting the upper pot on, I put it on when the water is cold. The reason is this:

The vacuum system works because the heat generated in the bottom pot causes the air above the water to expand, forcing the water up the siphon tube into the upper globe. The benefit is that the water is forced into the upper globe before reaching the boiling point therefore keeping the temperature below that which would cause the extraction of the bitter acids from the coffee beans. With a candy thermometer I find that using this method steeps the coffee at about 195 degrees.

It seems to me that bringing the water almost to the boiling point first, will create an environment where the water is too hot for optimal coffee extraction. It would defeat the entire purpose of using the vacuum method.

At least that is my opinion.

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