Welcome to Further Details, a series dedicated to ubiquitous but overlooked elements hidden on your favorite products. This week: the mysterious knob on a Chemex.
Since 1941, coffee nerds have used Chemex coffeemakers to make clean, delicious cups of pour-over coffee. The brewers are made of a single piece of borosilicate glass finished with a wooden collar and tie, serving as an insulated handle. The smooth glass is accented by a “button” with no discernible use that juts out on the bottom of the carafe below the pouring spout. Some have questioned the purpose of the button, and its usage is buried deep within Chemex’s brewing guide.
Peter Schlumbohm, Ph.D., designed the Chemex to look good, be easy to use, and, most importantly, brew a delicious cup of coffee. Schlumbohm was so obsessed with refining everyday tools that he developed over 300 patents during his career, the Chemex being his most famous. His invention was a success: the Chemex is a fixture at the Museum of Modern Art and the Smithsonian and remains a favorite among coffee enthusiasts and professionals. From the hourglass shape to the heat-resilient material, everything about the design is meant to produce a high-quality cup of coffee. So what’s the weird nipple-looking thing on the bottom of the brewer?
Per the manual: it marks where half the carafe’s volume is, with full volume falling at the bottom of the spout.
In Chemex vernacular, a “cup” of coffee is a humble 5 ounces, and not the standard 8 ounces. Therefore a six-cup Chemex holds 30 ounces of coffee and the button marks 15 ounces. (This is applicable to all Chemex sizes except the three-cup brewer, where the button denotes full volume.) The company’s brewing guide recommends one rounded tablespoon of coffee for every five ounces of coffee, so the button makes it easy to eyeball how much water you need to pour to achieve Chemex’s water-to-coffee ratio. So if you want a 15-ounce brew (in a six-cup Chemex), use three tablespoons of ground coffee, wait for the carafe to fill up to the button and toss the filter once it hits the mark.
For the coffee-obsessed, the button is a fruitless feature. Chemex’s maker likely didn’t expect at-home coffee geekery to escalate to a point where $150 kettles and scales were the norm. Modern coffee people will rarely eyeball their coffee measurements, instead brewing by weight rather than volume. Volume is a fickle measurement that is subject to irregularities in coffee beans, like varying densities and ragged shapes. This Reddit post shows how the same coffee bean at three roast levels can vary in volume but have the same weight. Weighing out coffee makes a final product that can be replicated and adjusted accordingly over multiple brews.
The Chemex button is a relic of its time, long before the third wave coffee movement, when coffee drinkers were less equipped at home, and most serious consideration pertained to the speed with which caffeine would transfer from bean to bloodstream. But hey, if you don’t have a scale, at least you can rely on a weird bump to guide your brews.