A two-chamber glass brewer that uses vapour pressure and then a vacuum. Water in the lower globe is heated until expanding vapour pushes it up a tube into the upper chamber, where it steeps with the coffee at close to full immersion. Taking the heat away cools the lower chamber, the trapped air contracts, and the resulting vacuum draws the brewed coffee back down through a filter — cloth in most traditional models — leaving the grounds behind.
Coffee-to-water ratio
55–70 g per litre (typically 65)
Grind
Medium to medium-coarse. Finer than a French press despite the full immersion, because the filter is doing real work rather than just holding a plunger.
Water temperature, as commonly used
88-96 celsius (typically 92)°C
Contact time
60-120 seconds (typically 90)
Skill level
advanced
Descriptive grind labels like this are illustrative starting points, not precise measurements — the same label can mean different particle sizes on different grinders. See the grind size guide for how to dial this in on your own equipment.
In short
A siphon, or vacuum pot, is two glass chambers joined by a tube, with a filter between them and a heat source underneath. Water starts in the bottom, rises to the top to brew, and returns to the bottom as finished coffee.
It looks like theatre, and the theatre is real physics. The useful thing to understand is that a siphon steeps the coffee fully and then filters it as a separate step, which is why it gives an unusually clear cup for an immersion brewer.
The journey up and back down
Widely documented
1
Heat the lower chamber
Water in the sealed lower globe is heated. As it warms, the air and vapour above it expand and press down on the water's surface.
2
The water rises
That pressure pushes the water up the tube into the upper chamber. A little always stays behind below the end of the tube, which is normal.
3
Add coffee and steep
Grounds are stirred into the hot water in the upper chamber. The heat stays on low, holding the water up and at a steady temperature while the coffee steeps.
4
Remove the heat
As the lower chamber cools, the vapour inside it contracts and the pressure falls below that of the room.
5
The draw-down
The pressure difference pulls the brewed coffee down through the filter into the lower chamber, leaving a dome of grounds above.
An explanatory diagram of the sequence, not a timed recipe. How long each stage takes depends on the heat source and the size of the brewer.
Why the cup is clear and full at once
CoffeeHQ explanation
Most brewers make one mechanism do two jobs. A French press steeps well but filters coarsely, so it is full and silty. A paper pour-over filters finely but extracts as the water passes, so it is clean and lighter. A siphon steeps the whole dose at a stable, fairly high temperature and then draws the liquid through a filter with some force.
With the traditional cloth filter, more oil passes than through paper, while most fine particles are still caught. The result tends to be clearer than a press and rounder than a paper pour-over. With a paper or metal disc, expect it to move towards those brewers' characteristics.
Starting figures for a siphon
Typical range
Starting figures for a siphon
Variable
Typical range
What moving it does
Coffee to water
About 55–70 g per litre (roughly 1:14 to 1:18)
Grind
Medium to medium-coarse
Finer than for a French press, because the steep is short.
Water temperature in the upper chamber
About 88–96 °C
Kept there by low heat. Too much heat makes the brew bubble hard and turn bitter.
Steep time
About 1–2 minutes
Counted from when the coffee is stirred in, before the heat comes off.
Conventional starting points. The draw-down adds time that these figures do not include, and it varies with the filter and the grind.
What to change first, and what to leave alone
CoffeeHQ explanation
A siphon has more to watch than most brewers and fewer things worth changing. The steep is short and fully immersed, so it behaves more like a press than a pour-over, with one addition: the heat is still on while it brews.
Brew one and watch three things. Whether the water rose cleanly and stayed up, how hard the surface bubbled during the steep, and how long the draw-down took once the heat came away. Then taste it.
Change the heat first. Once the water is up, the heat only has to hold it there. A surface that boils and churns is the usual reason for a harsh cup, so turn the heat down before touching anything else.
Then the steep time. Weak or sharp with a calm steep: let it steep a little longer before taking the heat away. Heavy or bitter: a little less. Keep the stir the same each time, since stirring changes the brew as much as time does.
Then the grind. The grind sets how the draw-down goes as well as how the cup tastes. If the draw-down drags, grind a step coarser; if it rushes and the cup is thin, a step finer.
Check the filter before blaming the recipe. A stale note that returns whatever you change is usually the cloth, not the coffee. Wash and store it as its maker describes, and replace it when it stops sealing or will not come clean.
Make the amount the brewer is built for, following the levels its instructions give, and let the glass cool before taking it apart. The siphon maker page covers handling hot glass and the burner.
Faults particular to vacuum brewing
CoffeeHQ explanation
The water rises only part of the way, or falls back early
Usually because: The seal between the chambers is not airtight, so pressure escapes instead of lifting the water.
Change first: Reseat the upper chamber squarely and check the rubber gasket.
The draw-down stalls with coffee stuck above
Usually because: The grind is too fine or the filter is clogged with old oils, so liquid cannot pass.
Change first: Grind coarser, and clean or replace the cloth filter.
Harsh and bitter
Usually because: The heat was left too high during the steep, so the coffee was boiled and agitated instead of held.
Change first: Turn the heat down as soon as the water has risen.
Usually because: A cloth filter that was allowed to dry out holds coffee oils that have gone off.
Change first: Store the rinsed cloth wet in clean water in the fridge, and replace it periodically.
A European invention kept alive in Japan
Accounts differ
Vacuum coffee makers appeared in Europe in the first half of the nineteenth century, with early designs and patents associated with Germany and France in the 1830s and 1840s. Accounts differ on who should be credited with the first, and the device was reinvented several times.
It fell out of everyday use in most places once simpler brewers became common, but it remained a fixture of Japanese coffee houses, where the careful, visible preparation suited the style of service. That history is why the siphon is often assumed to be Japanese in origin.
What to do next
Japanese siphon coffee — How the method is practised in the coffee houses that preserved it.
Siphon or pour-over? — Compares the two if you are choosing between effort and convenience.
Cloth coffee filters — Care of the filter is the part of siphon brewing most often got wrong.
Compare brewing methods — Places the siphon beside other brewers on body, clarity and skill.
The siphon as an object — Burners, filters and their upkeep, and what one maker's instructions say about handling hot glass.
Become a barista — A structured programme from dose and grind through milk, drinks and maintenance.
How this method is usually described
Full immersion at a stable, comparatively high temperature extracts efficiently, and the filter then removes the fines — so the cup is unusually clear for an immersion brew and fuller-bodied than paper pour-over, particularly with the cloth filter most traditional models use. Clarity and body at the same time is what the method is valued for, and it is a genuine consequence of separating the steep from the filtration rather than making one do both.
A description of the usual expectation, not a measured result. The coffee, its roast, the water and how it is brewed change the cup at least as much as the brewer does.
Water rises only partly, or falls back before brewing
A dry crust of grounds floating on top, so only part of the dose extracts
The draw-down stalls with liquid stuck in the upper chamber
Bitterness from leaving the heat on during the steep
Seat the upper chamber squarely so the seal holds, and stir when the water arrives so nothing floats dry. If the draw-down stalls, the filter is clogged or the grind is too fine. Take the heat away as soon as the steep is done rather than holding it there.
Rinse both chambers immediately; a cloth filter must be rinsed thoroughly with no detergent and then kept wet — stored in clean water in the fridge, or frozen. A dried-out cloth goes rancid from the oils it holds and will taint the next brew.
Glass is the fragile part: the chambers crack from thermal shock or from being over-tightened. Replace the filter cloth and its spring clip when the cloth stops sealing against the rim.
Each step links to its own page; this is the order they belong in.
I have coffee and a brewer
You own something to brew with and want a good cup from it.
Find your brewer's page, start from its recipe, and change one thing at a time. The later steps are for when the cup is not right, and for finding out why a change worked.
1Find your brewerWhat it does to the coffee, and a starting recipe labelled as a starting point.
2Work out the amountsCoffee and water for the cup you are making; the recipe scaler follows from it.
3If the cup is not rightChoose the brewer, tick what you noticed: the quickest check, and one change.
4One change per brewThe same loop written out for filter coffee, from the first brew to a recipe you keep.
5Why the change worksStrength and extraction as two numbers, and what a taste can and cannot tell you.
6Test it yourselfHow to compare two cups so the difference is the thing you changed.