Vacuum Coffee Maker: How It Works and Why Glass Matters
A vacuum coffee maker uses heat and pressure to brew coffee inside sealed glass. Water in the bottom flask is heated until vapor pressure pushes it up into the funnel above, where it meets the coffee grounds. When the heat is removed, the flask cools, a vacuum forms, and the brewed coffee is pulled back down through a filter into the flask below.
The Kazumi vacuum coffee maker (also called a siphon or syphon brewer) does this entirely in borosilicate glass - from the flask, through the condenser and funnel, all the way through the glass filter. Nothing else touches your coffee.
This is the purest way to brew coffee.
How the Kazumi vacuum coffee maker works
The Kazumi has three glass pieces that stack into one brewing system.
The flask sits at the bottom. It holds the water.
The condenser sits in the middle. It is a Kazumi-designed piece - a coiled borosilicate glass channel that helps keep the brewing water at the ideal extraction temperature (just below boiling) for the entire brew. No other siphon coffee maker has this. Without it, the water temperature drifts and extraction is inconsistent. With it, every brew stays in the ideal range.
The funnel sits at the top. It holds the coffee grounds. At its base is a fused borosilicate glass filter - no paper, no cloth, no metal. This is a Kazumi-only design.
Here is what happens when you brew with the Kazumi vacuum coffee maker:
Heat the flask. As the water heats, vapor pressure builds inside the sealed flask. Once the pressure exceeds atmospheric pressure, water is pushed up through the condenser and into the funnel, where it meets the coffee grounds. The condenser helps keep it at ideal temperature the whole time. Brewing lasts about 90 seconds.
Take the brewer off the heat. The flask cools. A vacuum forms inside the flask. The vacuum pulls the brewed coffee downward through the glass filter and back into the flask. The grounds stay in the funnel above.
Start to finish, brewing takes 5 to 8 minutes depending on your heat source.
Every drop of your coffee touched only glass. No plastic. No paper. No metal.
The history of vacuum brewing
Vacuum brewing is one of the oldest coffee methods still used today. Invented by Loeff of Berlin in the 1830s, the vacuum coffee maker was already producing the cleanest cup in Europe when drip coffee makers, moka pots, and pod machines were still a century or more away. Reference: Wikipedia - Vacuum coffee maker.
In Japan, vacuum brewing became the cornerstone of coffee craft. Nearly 200 years of refinement of the same original method - because the physics that produced the cleanest cup in 1840 still produces the cleanest cup today. The Kazumi is the modern expression of that same 200-year-old method, refined into an entirely glass system that brings the same purity into your home kitchen.
What makes the Kazumi different
Every part of the Kazumi that touches water or coffee is thick borosilicate glass - the same material used in medical syringes, pharmaceutical vials, and surgical equipment. Chemically inert. Non-reactive. Non-porous.
- The flask is thick borosilicate glass
- The condenser is thick borosilicate glass (Kazumi-only design)
- The connecting tube is thick borosilicate glass
- The funnel is thick borosilicate glass
- The filter at the base of the funnel is fused borosilicate glass - the only glass filter of any vacuum coffee maker made anywhere
No plastic anywhere. No metal in the brew path. No paper filter to buy or throw away. No cloth filter to wash or replace.
Why glass matters for your coffee
Plastic parts in a coffee maker leach chemicals and microplastic particles into the water. A 2025 study on plastic kettles, published in npj Emerging Contaminants (Nature), measured approximately 3 billion nanoplastic particles released into a single 250ml cup on the first boil. Even after 150 uses, plastic kettles were still releasing 205 million particles per cup. Read the study.
Metal filters change the taste of your coffee. They leave a faint metallic edge and pass fine sediment through into your cup. Paper filters strip coffee oils out of the brew - and that is where much of the flavor lives - then get thrown away after every use. Cloth filters strip oils the same way, pass sediment through, and hold onto residue that stains over time and eventually needs replacing.
Borosilicate glass does none of that:
- Chemically inert - it does not release anything into water, hot or cold
- Non-porous - it does not absorb coffee oils or carry flavors between brews
- Does not stain - warm-water rinse is enough
- Does not stick - grounds and residue release cleanly
- Reusable indefinitely - the same glass filter serves you for a lifetime
We covered the full case for glass over plastic and metal in our guide to glass coffee makers. The short version is: only glass adds nothing to your coffee, and only a fully all-glass brewer removes every non-glass surface from the brew path.
The Kazumi works on any stove
The Kazumi vacuum coffee maker runs directly on any regular stove - gas, electric, or induction. No dedicated equipment. Or pair it with the Kazumi Toki, a compact ceramic stove built specifically for it.
Traditional vacuum coffee makers require alcohol or oil burners. Those need well-ventilated setups (often outdoor or with specialty exhaust), extra fuel to keep in the house, and one more step every time you want to brew. The Kazumi eliminates that. It sits on your stovetop like a kettle.
Frequently asked questions
Is a vacuum coffee maker the same as a siphon coffee maker?
Yes. Vacuum coffee maker, siphon coffee maker, syphon coffee maker, and vac pot all describe the same brewing device. The names describe different aspects of how it works. The Kazumi vacuum coffee maker is built from three glass pieces: the flask (bottom), the condenser (middle, Kazumi-only), and the funnel with its built-in glass filter (top).
How long does the Kazumi vacuum coffee maker take to brew?
Start to finish, 5 to 8 minutes depending on your heat source. The actual contact between water and coffee grounds is around 90 seconds.
Do you need a special stove for the Kazumi vacuum coffee maker?
No. The Kazumi runs directly on any regular stove - gas, electric, or induction. You can also pair it with the Kazumi Toki, our compact ceramic stove designed for it. Traditional vacuum coffee makers require alcohol or oil burners, which need ventilation (often outdoor or with specialty exhaust) and add an extra step to every brew. The Kazumi removes that step entirely.
Are Kazumi vacuum coffee makers hard to clean?
No. Borosilicate glass is non-porous, so coffee oils rinse straight off with warm water. It does not stain, does not stick, and does not absorb flavors between brews. No detergent, no scrubbing. The glass filter rinses clean the same way and lasts a lifetime.
How much coffee do you use in the Kazumi vacuum coffee maker?
The Kazumi uses 55 grams of medium-ground coffee to 800ml of water. Adjust to taste - stronger with a little more, milder with a little less.
Is a vacuum coffee maker worth it?
Yes. The Kazumi is the purest way to brew coffee. No other brewer keeps every part of the brew path in glass, including the filter. If you want to taste your beans without plastic, without metal, and without paper in the way, the Kazumi is the answer.
Bottom line
The Kazumi vacuum coffee maker is the purest way to brew coffee. No plastic in the brew path. No metal. No paper. No cloth. Just glass, water, and coffee.
If you want the cleanest, most complete cup your beans can produce - the taste of the coffee itself, with nothing added and nothing subtracted - the Kazumi is the answer.
Shop the Kazumi Vacuum Coffee Maker
Learn how siphon brewing works
Why glass beats plastic and metal