The cappuccino’s name has nothing to do with foam looking like a monk’s shaved head. It comes from the brown robes of Capuchin friars. In the late 1700s, Viennese coffee houses under the Habsburg monarchy served the Kapuziner, black coffee with a few drops of cream to match that shade, alongside the lighter Franziskaner for the Franciscans. The drink passed into Italian through the port of Trieste and appeared as cappuccino in 19th century texts. The modern version needed two inventions: commercial refrigeration, which let cafes keep fresh milk instead of long-lasting heavy cream, and the espresso machine with its steam wand.

That wand turns milk into microfoam. Baristas steam to 55 to 65 degrees Celsius, since past 70 the milk smells of sulfur; heat unfolds whey proteins whose water-hating ends wrap around injected air bubbles and armor them, while warming lactose makes the milk taste sweeter with no added sugar. Italy locked in the math at one third espresso, one third steamed milk, and one third foam, starting from 25 milliliters of espresso in a cup of 180 milliliters at most. Stretched into a 20-ounce cup, the balance collapses, which is why variations get their own names: the macchiato, the Spanish cortado, and the flat white, which lacks the stiff dome of foam.

• World Barista Championship rules demand a single espresso shot, a 150 to 180 milliliter cup, and at least one centimeter of foam.
• The Greek freddo cappuccino whips cold skim or low-fat milk into a dense foam called afrogala, because fat blocks cold foaming.
• Italians avoid cappuccino after 11 a.m. and after big meals, a rule rooted in 19th century beliefs about digesting hot dairy fat.
• New York’s Caffe Reggio claims it introduced the cappuccino to the US in 1927.
• Oat milk lacks the whey proteins that armor bubbles, so barista blends add vegetable oils and stabilizers to mimic them.