Guide · Siphon coffee

Siphon coffee (vacuum brewer)

A siphon, also called a vacuum coffee maker, vac pot or syphon, brews in two stacked chambers. Heat pushes the water from the lower bowl up into the coffee; when the heat comes off, the cooling lower bowl pulls the finished coffee back down through a filter.

Updated 2026-10-21 · sources listed at the end

How a siphon works

The lower bowl is sealed by the upper bowl's tube. Heating the water raises its vapor pressure and the pressure of the trapped air; once that exceeds the air pressure outside, water is pushed up the tube into the upper bowl. Water vapor is about 1/2000 as dense as liquid water, so the mixture expands quickly. Continuous heat holds a small pressure difference, about 1.5 kPa (0.015 atm), and keeps the water up while the coffee steeps just below boiling. Take the heat away and the lower bowl's pressure drops: the vapor condenses and the coffee is drawn down through the filter, leaving the grounds above (Wikipedia).

That makes the siphon a full-immersion brewer, like the French press, with a filter at the end; HARIO Europe notes that the water stays hot throughout. The moka pot uses the same vapor-pressure lift, but forces the water through a packed bed of coffee at higher pressure.

Upper bowl, open at the top; the coffee steeps here.
Filter (cloth, paper, metal, nylon or a glass rod) with a chain or spring hooked down the tube.
Tube reaching almost to the bottom of the lower bowl.
Seal where the upper bowl sits in the lower bowl's neck; without it, no pressure builds.
Lower bowl: holds the water, and later the finished coffee you serve from.
Heat source: an alcohol lamp, butane burner, gas or an electric heater.

Heating raises the vapor pressure and air pressure in the sealed lower bowl.
Once that exceeds outside air pressure, water rises; about 1.5 kPa of difference holds it up (Wikipedia). A little water stays below.
With the heat lowered, the coffee steeps just under boiling: about 200 °F / 93 °C in Sprudge's method.
Heat off: the vapor condenses, pressure in the lower bowl drops and the coffee is drawn through the filter, leaving the grounds on top. In Barista Hustle's tests this began when the slurry was about 91–92 °C.

Drawn by pourxlab.com for this page from the operating principle described by Wikipedia (source 1), HARIO (sources 3–4), Sprudge (source 7) and Barista Hustle (source 8). Not to scale; a generic two-chamber brewer, not any maker's design.

Step by step

This method combines the published guides compared in the table below; the time on the heat is where they differ most.

Weigh. A starting point is 1:16: Sprudge uses 35 g of coffee for 560 g of water. HARIO Europe's 10 g per 120 ml (1:12) makes a stronger cup. See the ratio calculator for other sizes.
Grind medium to medium-fine. Sprudge describes a medium grind "like beach sand"; HARIO UK suggests medium-fine. On the grind size chart that sits with the medium rows, such as the SCA drip category.
Prepare the filter. Soak a cloth filter in warm water, or rinse a paper filter under hot water. Feed the chain down the tube and hook it to the bottom.
Fill the lower bowl with water already heated in a kettle; both HARIO Europe and Sprudge say this is faster. Dry the outside of the glass.
Heat and seat. Light the burner and rest the upper bowl in the neck at an angle. When small bubbles rise from the chain, set it straight and press down gently to seal (HARIO Europe); Sprudge twists it in when the water is near, but not at, a rolling boil.
Lower the heat as the water rises, so that it stays up: Sprudge turns the flame down until it is just visible.
Add coffee and stir. Start the timer and stir gently until all the grounds are wet; HARIO UK says 3–5 circular stirs is usually enough. Adding the grounds cools the water by 2–3 °C, and it recovers in about 30 seconds (Barista Hustle).
Steep. 40–60 seconds (HARIO Europe), 70 seconds (HARIO UK) or 2 minutes with a second gentle stir at 0:30 (Sprudge).
Remove the heat. Give a few gentle stirs (HARIO UK: three) and let the coffee draw down; Sprudge expects about 1.5 minutes. A hard stir builds a dome of grounds.
Serve from the lower bowl once the coffee has fully drained, after lifting off the upper bowl.

Published recipes side by side

Wide table — scroll sideways on a phone.

Source	Coffee : water	Grind	Time on heat with coffee	Notes
HARIO Europe	10 g : 120 ml per cup (1:12)	not given	40–60 s	water boiled in a kettle first
HARIO UK	17 g : 250 g (15–17 g suggested, ≈1:15–1:17)	medium-fine	70 s	3–5 stirs at the start, 3 after the heat is off
Sprudge	35 g : 560 g (1:16)	medium, "like beach sand"	2:00	205 °F water; brew about 200 °F; drawdown about 1.5 min
HARIO USA, Morgan Eckroth	36 g : 560 ml (≈1:15.6)	not given	about 2:30 total	—

For comparison, the lab's filter ratio band is 1:15–1:18; most siphon recipes sit inside it, and HARIO Europe's per-cup recipe is stronger.

Temperature in the upper bowl

Just under boiling. Wikipedia puts brewing slightly below 100 °C (212 °F); Sprudge aims for about 200 °F (93 °C) once the flame is lowered. Water boils at a lower temperature at altitude; the temperature converter estimates your boiling point.
Stable, not falling. Unlike a pour-over, the temperature stays flat through extraction (Sprudge). In Barista Hustle's tests it kept rising slowly until the water in the bottom chamber ran low.
More flame, more heat. A higher flame makes more steam and a hotter brew; seating the upper bowl too early or running the flame too low early on can leave the brew at the low end (Sprudge).

Filters

Siphon filters are cloth, paper, metal or nylon screens, or a glass rod (Wikipedia). HARIO's Technica siphons come with a cloth filter and its NEXT siphons with cloth and metal filters; paper filters are sold separately. Sprudge brews with paper and finds cloth impractical for regular use because of the cleaning involved. The glass filter rod was designed in 1932 by Raymond Kell of the MacBeth Evans Glass Company (Harris).

Safety

Leave a little water in the lower bowl. HARIO Europe warns against dry heating, and Barista Hustle warns that a bottom chamber left to dry out completely can shatter.
Do not fill an alcohol lamp to the top, put the flame out carefully and use oven mitts: the parts get hot (HARIO Europe).

Troubleshooting

Problem	Likely cause	Try
Water does not rise	Upper bowl not sealed in the neck	Set it straight and press down gently (HARIO) or twist to seal (Sprudge)
Water drops back too early	Heat turned too low; it is the heat that holds the pressure	Lower the flame only until it is just visible
Thin, sour, hollow	Under-extracted	Grind finer, keep everything else the same (Sprudge)
Bitter, harsh, astringent	Over-extracted	Grind coarser (Sprudge)
Drawdown stalls	Brewer filled near its capacity, or a hard stir domed the grounds	Brew a smaller batch; stir gently back and forth (Sprudge)
Brew seems cool	Upper bowl seated too early, or flame too low early on	Check with an instant-read thermometer before adding coffee
Lower bowl nearly dry	Too long on the heat	Take the heat away; never let it run dry

A short history

Year	Event	Source
1827	Johann Nörrenberg describes the vacuum coffee maker	Wikipedia
1830s	Earliest glass vacuum pots in use in Germany, including one by Loeff of Berlin	Harris
1835	Louis François Boulanger files a French patent for a vacuum pot	Harris
1840	Scottish engineer James Robert Napier presents the side-by-side Napier vacuum machine	Wikipedia, Harris
1841	Mme. Vassieux of Lyon patents her double-globe glass balloon in France	Harris
1915	Corning introduces Pyrex heat-resistant glass, solving the cracking of early glass pots; Silex brewers use it	Harris
c. 1925	Gerhard Marcks and Wilhelm Wagenfeld's Sintrax, made in heat-resistant glass by Schott in Jena, now in MoMA's collection	MoMA
1930s–1950s	The most popular brewing method in American homes, from the early 1930s to the mid-1950s	CoffeeGeek
1948	HARIO's first siphon, the beginning of its coffee range	HARIO Europe
c. 1950	A three-part Silex vacuum maker of this date is in the Corning Museum of Glass	CMoG
c. 2007	Renaissance among coffee professionals	Sprudge

Siphons fell out of everyday use in the West in the mid-20th century as too complicated for daily brewing, but stayed popular in parts of Asia, including Japan and Taiwan (Wikipedia).

Lab tip: time two things. Write down how long the coffee sits in the upper bowl with the heat on, and how long the drawdown takes. If the cup changes and the times have not, look at the grind.