Chemex Basics: What the Thick Filter Does
The Chemex was designed in 1941 by a chemist who borrowed the shape from laboratory glassware. The form has barely changed since, and not only for looks: each part of it does something to the coffee.
What the thick filter does
The defining feature is the proprietary filter paper, twenty to thirty percent thicker and considerably denser than ordinary filter papers. That thickness essentially sets the character of Chemex coffee.
A thick paper traps far more of the coffee oils and fine particles. The result is a very clear, clean cup with a tea-like transparency, and acidity comes through distinctly because there is little else muddying it.
There is a cost. Removing the oils also removes body and the weight that fills the mouth. If you like heavy, syrupy coffee, a Chemex will taste thin to you. That is the character of the brewer, not a defect.
A standard recipe
A Chemex is usually used to brew several cups at once. The figures below are for roughly two.
Grind coarser than you would for a V60, because the thick paper slows drainage. At the same grind, the longer contact time pushes you into over-extraction.
Folding the filter and the air channel
Chemex filters fold into four layers. What matters is putting the three-layer side towards the spout.
There is a groove on the spout side of the glass that lets air escape. Block it with paper and pressure builds inside, and the water refuses to drain properly. The thick side keeps that channel open.
Rinsing matters more here than elsewhere. A thicker paper carries a stronger paper taste, so run plenty of hot water through it and discard that water before you start.
When it will not drain
The most common Chemex complaint is a brew that slows to a crawl or stops altogether. The thick paper makes this easy to trigger, and it is nearly always one of three things.
When a Chemex is the right choice
It is not a universal brewer but one with a clear personality, and it rewards being used deliberately.
It pairs particularly well with light to medium roasts that have acidity, because removing the oils lets that acidity read cleanly. For the weight of a dark roast, a French press serves better.
It also shines when you are brewing for several people. The brewer and server are one piece, so nothing needs decanting, and it looks presentable on a table.
Recording grind and time keeps the slow drawdown repeatable. Optimal grind differs between a Chemex and a V60 for the same coffee, so log them separately.