Two glass chambers, a heat source, and a vacuum. Water is driven upward into the coffee by vapour pressure, steeps as a full immersion, then gets pulled back down through a filter when the heat comes off. It is the most theatrical brewer in coffee and the one most often dismissed as theatre — which is a shame, because the cup it makes is genuinely hard to get any other way.

What it actually does

Every other brewer makes you choose. Immersion gives you body and forgiveness but muddies the high notes; percolation gives you clarity but the bed has to manage flow while you pour. The siphon refuses the choice: the coffee steeps fully submerged, like a French press, and then the entire brew is pulled through a filter in one go, under vacuum.

So you get immersion's even extraction — every particle sat in every gram of water for the same time — with a filtered cup at the end. Clean and round at once. On a delicate washed Ethiopia that's a combination a V60 can't quite reach.

How the physics works

Water goes in the lower bulb, over the heat.
As it heats, vapour pressure builds and pushes the water up the siphon tube into the upper chamber, where the coffee is waiting. A little water always stays behind — that's normal and necessary.
The brew steeps up top, at a temperature the heat source is still holding.
Remove the heat. The vapour in the lower bulb condenses, pressure drops below atmospheric, and the resulting vacuum pulls the brewed coffee down through the filter.

The drawdown is not gravity. It's the atmosphere pushing the coffee through the filter for you, which is why a siphon can use a cloth filter and still finish in under a minute.

The recipe

Ratio: 1:15. 20 g coffee, 300 g water is a comfortable two-cup brew.
Grind: medium — around your V60 setting, or a click coarser. Finer than French press.
Water: start with hot water in the lower bulb, not cold. Cold water means minutes of the burner running while the upper chamber and the coffee sit there heating up dry.
Steep: 60–90 seconds once the water is up.

The part that decides the cup

Stirring. It matters more here than anywhere else in filter coffee, and it's where most siphon brews are won or lost.

When water first arrives in the upper chamber it pushes the grounds into a dry raft floating on top. Left alone, a good part of your dose never properly wets. So:

Stir once, immediately, as soon as the water is up — enough to break the raft and sink the grounds. Gentle, a few strokes.
Stir once more just before you kill the heat. This re-suspends what has settled and evens out the last of the extraction.
Don't stir throughout. Constant agitation over 90 seconds of full immersion pushes you straight past the sweet spot into bitter, and drags fines into the filter so the drawdown stalls.

Two stirs. That's the whole technique.

Filters, and what each one costs

Cloth is the traditional choice and the one the Japanese kissaten tradition kept alive. It passes some oils, so the cup keeps a little weight. It also has to be stored wet, in the fridge, and replaced regularly — a dried-out cloth filter tastes exactly as bad as it sounds.
Paper gives the cleanest cup and no maintenance at all. If the ritual is not the point for you, start here.
Metal passes the most oils and some fines. Heaviest body, least clarity, zero upkeep.

Heat

A butane burner is cheap and works. A halogen beam heater is expensive, beautiful, and easier to control — it responds instantly when you move it away, which matters because removing the heat is a brewing step, not just the end of one. An alcohol lamp is the traditional option and the least controllable.

What goes wrong

Cold start. The single most common mistake. Everything after it is compromised.
Never stirring. Half your coffee floated. The cup reads thin and sour and you'll blame the grind.
Grind too fine. The vacuum drawdown stalls, the coffee sits in contact far too long, and you get bitterness with the cleanliness still intact — an oddly unpleasant combination.
Pulling the heat too late. The steep keeps running while you decide. Commit to a time and take the heat off on it.

When to reach for it

When you have a coffee whose aromatics you want and whose body you don't want to lose. When you're brewing for two and want it to be an event. When you already brew good pour-over and want a genuinely different axis to explore rather than another cone.

Not when you're in a hurry, and not as a first brewer. It rewards attention, and asks for it every time.

Siphon