How to Make Coffee With a Vacuum Brewer (and Its Physics)

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For my daily morning coffee, I use a French press. But for the special occasion, I break out the Cona Vacuum Brewer which makes an even better coffee in my opinion. This is the Cona D Size Vacuum brewer which can make up to 32 ounces of coffee. My normal tumblers are 16 oz so I can get two good mugs out of this. Cona also makes a C Size, which is 24 ounces.

The Cona Vacuum brewer consists of a large glass bowl connected to a siphon tube at the bottom with a rubber seal, and inside the tube is a filter that looks like a little glass rod. I call it a filter because it prevents the coffee grounds from entering the pot. There's the glass pot and the stand that holds all of the components, and finally, a spirit lamp that consists of a suffer lid, the part that holds the wick, and the glass dish that holds the fuel.

To actually get the water to a boil, I won't be using the spirit lamp to do so. You can if you'd like, but it would take a long time to bring it up to temperature. I personally use an electric kettle, but you can boil it in a pot on the stove, or microwave the water to boiling temperatures if you want. Since my mug is 16 ounces, I'll pour two mugs and start the kettle.

In the meantime, it's important to make sure that the glass rod filter isn't stuck to the upper glass bowl before pouring the grinds into it. This can happen when you're air drying the components with the filter in the bowl, and you let it sit for too long. When that happens, the water may not be pulled out through the filter and you're stuck with a bowl full of coffee with grinds in it.

Let's consider the coffee. It's recommended that you add one scoop (or one tablespoon) of coffee per 4 ounces of water. That would mean 8 scoops for 32 ounces, which is what I'm making. However, I've found that to be a little too strong for my taste, so I just use seven slightly overfilled scoops. The number of scoops is entirely up to your taste.

Let's talk about the level of grind. You will want to use between a medium and fine grind for your coffee beans. If you grind it too fine, you run the risk of the vacuum not being able to suck the water through the siphon tube because the grinds can clog the filter. If you make it too coarse, the water pulls through too quickly and you could get a weaker coffee. I'm using pre-ground coffee that was ground to medium. When I grind the beans myself, I usually set my burr grinder in between medium and fine.

You'll want to make sure that the spirit lamp is filled, because that will be the main method to maintain the temperature of the heated water. You'll want to use denatured alcohol, which is available at any home improvement store. Replace the wick and lid.

Once the water comes to a boil in the kettle, pour it into the glass pot. Make sure that the outside of the pot is completely dry. The temperature difference between the boiling water inside the pot and any water droplets outside the pot can cause thermal stress in the glass and shatter it. Place the pot back into the stand.

You'll now want to light the spirit lamp. Take off the lid and start up the lighter. The lamp should light up immediately. After a minute or so, the water will start to bubble a bit at the bottom of the pot.

Re-arrange the bowl to be on top of the pot, making sure that the siphon tube goes into the water. While holding onto the pot's handle, gently push the upper bowl while slightly twisting it into the opening of the pot. Now you just wait for the water to flow up to the top. The clock at the bottom right will show the time it takes for the water to seep up from the pot to the bowl.

The basic principle is that as the water boils, it's forced by temperature and pressure through the siphon tube, even when the glass rod is in that tube. Once the water has traveled to the top bowl where the coffee grinds are, you snuff out the flame, which causes a drop in temperature and a negative pressure in the pot. At that point, the water should seep back down through the siphon tube around the tight tolerance of the glass rod, and into the pot - leaving the grinds in the top container and resulting in pure coffee in the pot.

You'll notice the water slowly seeping into the grinds, making a muddy mixture. Unlike a French press, not all of the water is in contact with the coffee grinds at the same time. With a French press, you’re supposed to let it brew for about four minutes. However, I've never run across a recommended number of minutes for a vacuum brewer. Through trial and error, I find that a medium grind results in a total time of seven to eight minutes where there's at least some water in contact with the coffee.

At the five minute mark, all the water that CAN go up to the bowl is out of the pot. Not only do you see and hear the bubbling of the water in the pot, you can see it at the surface of the mixture in the top bowl.

I'm now gonna snuff out the flame with the lid. I'll restart the timer in the bottom right to show you how long it takes for the vacuum to pull the water down.

Notice that there's a little bit of water that remains in the bottom. That's because there's a clearance between the bottom of the siphon tube and the bottom of the pot. This means that if you make less than the full 32 ounces for this size brewer, you'll end up with a more diluted cup of coffee, because the volume of water that remains in the bottom is always a constant, no matter how many ounces you make.

You can see the coffee in the top bowl travel down to the pot. Unlike a French press, where you almost always find some residue of the grinds at the bottom of your cup, there's none, or almost none, with the vacuum press.

At the one and a half minute mark, you'll hear the gurgling sound of the water as the vacuum finds itself with no more liquid to pull down. At this point, the water's been in contact with the coffee grinds for a total of a little less than seven minutes, but as I said before, not all of the water is in contact with the grinds for the full seven minutes.

When the bubbling stops, you'll know that the coffee's fully extracted into the pot. While holding the pot's handle, you can now remove the upper bowl by gently twisting it off the pot's mouth, and returning it to its place in the stand.

So that's it. I find that the coffee isn't bitter at all, and you can really taste the subtle flavors of the type of coffee beans you're using. Since every component is made of glass, the only contact that that the coffee has - during the brewing process itself - is with the glass, as opposed to other types of brewers which may have some components made of stainless steel. My taste buds aren't as sensitive as others to stainless steel, but I've heard that it can make a difference.