This Coffee Machine Makes Cold Brew That Looks Like a Frothy Pint of Guinness

But, a word on oxygen. The device essentially pumps pure air (79 percent nitrogen, 20 percent oxygen) into the coffee rather than fuss with nitro cartridges. This is cool, but oxygen exposure is the known enemy of fresh-tasting coffee. After the nitro evaporated, side-by-side taste tests did show more flabby oxidation flavors in the nitro than the basic non-nitro.

But fresh off the machine, this doesn’t show up much. What you notice is bracing, fun bubbles that also add perceived sweetness. Those bubbles cover a lot of sins, building a dense head atop cold brew that looks for all the world like a well-poured Irish stout.

A WIRED editor, looking at a photo of Cumulus’ abundant nitro, jovially suspected chicanery. “I’d swear they used Guinness for the promo shots,” he wrote.

The espresso is likewise effervescent—endowed with a thick and genuine crema, formed through the pressure exerted by the device’s powerful compressor. It was the Cumulus espresso’s own natural frothiness that led to my handsomely foam-topped martini—a result that eluded me with chilled hot espresso.

A strong hat tip to cocktail consultant and educator Josh Seaburg, of Virginia’s Model Citizen Cocktails, for a good espresso martini recipe to try this stuff out on. For the record, this involved 1.5 ounces of vodka, 0.75 ounces of coffee liqueur such as Mr. Black, and a half-ounce of simple syrup, mixed with an ounce of cold espresso. Mix, shake, pour. The device makes only double shots, so one capsule provides enough cold espresso for two cocktails.

Who’s the Cumulus For?

On the one hand, the Cumulus is an impressive piece of engineering—one that succeeds on multiple fronts where other device makers have failed.

But it is not a device for coffee snobs. It lends itself best to those who prize the convenience of a Keurig and aren’t overly fussy, or those who’d naturally load up their cold brew with milk and sugar or other flavors. Cumulus doubles down on this with flavored syrups ranging from Orange Piloncillo to Cinnamon Demerara.