The Chemex
A funnel and a carafe blown from a single piece of glass, a thick paper folded into a cone, a groove to let the air out: the Chemex is a laboratory device that moved into the kitchen. It makes a filter coffee of several cups, served in the very vessel it dripped into.
Why does the Chemex need a groove?
Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.
The funnel and the carafe form a single piece, with no gap between the two. Nothing leaks anymore, but the air in the carafe has no way out.
Read the stages without animation
- A single piece of glassThe funnel and the carafe form a single piece, with no gap between the two. Nothing leaks anymore, but the air in the carafe has no way out.
- The coffee drives out the airEvery drop that falls takes the place of a little air in the carafe. With no outlet, the air pushes upward and slows the flow.
- The grooveA groove cut into the wall connects the carafe to the open air and also serves as a spout. The air escapes, the coffee goes down.
- The thick side of the paperThe three layers of the filter sit against the spout and keep it from blocking the groove. The air passage stays open to the end.
- ServeThe paper and its grounds are removed, and the coffee is poured from the same groove. The carafe becomes the server.
To remember: A one-piece carafe has to let the air out: the groove does it, and the thick side of the paper keeps it open.
In history: Peter Schlumbohm, in New York, from 1939 to 1941.
Read the full article and its sources ↓History
Peter Schlumbohm, a chemist based in New York, files on April 13, 1939 a “filtering device” that claims a German priority of April 13, 1938; US patent 2,241,368 is issued on May 6, 1941. He assigns half of his rights to Isaac Hatter, of Akron, Ohio. The text states the idea in one sentence: to join in a single piece the funnel that holds the paper and the flask that receives the filtrate, and the patent specifies that the device can also be used in the laboratory (source 1).
The discovery the patent recounts is unexpected. A funnel set on a flask always leaks enough to let the air out; once the two are welded together, the device no longer works, because the air driven out by the coffee has no outlet. Hence the groove cut into the upper wall, which serves both as an air passage and as a pouring spout. The flask has the well-known shape of the Erlenmeyer, chosen for stability, serving and cleaning with a brush (source 1).
A claim of the patent sets the angle: the walls of the funnel spread apart by sixty degrees, to firmly support a sixty-degree cone of paper (source 1). The same angle will give Hario's V60 its name, sixty-three years later.
Today's manufacturer, a family business in Massachusetts, presents Schlumbohm as the author of more than three hundred patents, inspired by the Bauhaus and by laboratory glassware; it says the glass is borosilicate, and the wooden collar and its leather tie are fitted by hand, and it recalls that the Illinois Institute of Technology ranked the Chemex among the hundred best-designed objects of modern times (source 2, according to the manufacturer). The presence in museum collections, which the manufacturer claims, has not been verified in the catalogs.
The motion
The round filter is folded in half then in four and opened into a cone, three layers on one side, one on the other. The thick side is placed against the spout: it keeps the paper from collapsing into the groove, which must stay free for air throughout the brew (source 2). This is exactly the role the patent gave to the groove (source 1).
The manufacturer recommends a medium to coarse grind: too coarse, the water rushes through; too fine, the grounds clog the filter (source 2). It counts the cup at five ounces, about 15 cl. Once the water has passed through, the paper is lifted out by its edges and thrown away, a motion that the patent presented as a new convenience for the housewife (sources 1 and 2).
The settings
- Grindmedium to coarse (source 2)
- Dosenot documented in the manufacturer's pages read (source 2)
- Brew rationot documented in the sources read; plate XV, section 04, uses 1:16 to 1:17
- Temperaturenot documented by the manufacturer; in 1921, Prescott preferred water at 85 to 93 °C to boiling water (source 6)
- Timenot documented in the sources read
- Pressurenone: gravity alone
What it has going for it
- Borosilicate glass imparts no taste, and glass already headed the list of materials recommended by Prescott in 1921 (sources 2 and 6).
- The device serves as a carafe: the coffee drips and is served from the same piece, with no transferring from one vessel to another.
- The cone is a single smooth piece, without crevices, designed to be cleaned with a brush (source 1).
What is held against it
- The slow Chemex paper drips more slowly than a V60 paper: 7.2 mL per second for the bleached Chemex against 11.0 for a tabbed Hario, in the same setup (source 3).
- The water passes through only a small zone of a large paper, which exposes the Chemex to clogging (source 4).
- If the paper collapses into the groove, the air no longer escapes and the flow stops (source 2).
- It needs filters shaped to the device, and the glass breaks.
What it gives in the cup
The Chemex gives a clear cup, with no sediment, low in oils: this is the effect of the paper, whose porosity governs what passes through (source 7). The manufacturer speaks of a “laboratory” paper of “heavy weight” (source 2); Gagné's measurements do not confirm that it is thicker, 210 microns for the bleached Chemex against 206 for a Hario, but do confirm that it is slower (source 3).
A slow paper lengthens contact and pushes extraction further if the grind is not coarsened in proportion, hence the manufacturer's advice. No published measurement of yield or concentration specific to the Chemex was found.
Anecdotes
- In Ian Fleming's novel From Russia, with Love (1957), James Bond makes his morning coffee in London, very strong, in a Chemex. The passage is reported by a specialist site; the novel itself was not reread (source 5).
The sources for this sheet
- Peter Schlumbohm, US patent 2,241,368 “Filtering device,” filed April 13, 1939 (German priority of April 13, 1938), issued May 6, 1941 · online · primary
- Chemex Corporation, pages “About Us,” “Materials & Process,” “FAQ” and “How to brew with Chemex” (according to the manufacturer), accessed October 21, 2026 · online · secondary
- Jonathan Gagné, “An in-depth analysis of coffee filters,” Coffee ad Astra, August 4, 2019 · online · secondary
- Jonathan Gagné, “The four rules of optimal coffee percolation,” Coffee ad Astra, March 4, 2021 · online · secondary
- The James Bond Dossier, “The Spy Who Loved Coffee,” accessed October 21, 2026, reporting Ian Fleming, From Russia, with Love, 1957 · online · secondary · reading: yes (novel not reread)
- William H. Ukers, All About Coffee, New York, 1922, ch. XXXVI (report by S. C. Prescott, MIT, November 1921) · online · primary
- M. Y. Rendón, M. B. dos Santos Scholz, N. Bragagnolo, “Physical characteristics of the paper filter and low cafestol content filter coffee brews,” Food Research International, 108, 2018, p. 280-285, doi:10.1016/j.foodres.2018.03.041 · online · primary · reading: abstract