Order a latte in an Italian cafe and you may get a plain glass of milk, because latte simply means milk; you need caffè latte or caffè e latte. The drink itself is precise: one or more shots of espresso topped with steamed milk in a glass of about 230 milliliters, milder and milkier than a 140 milliliter cappuccino and without its stiff foam cap. The key is microfoam. A steam wand unfolds milk proteins, which wrap around microscopic air bubbles in a stable emulsion, and heating to around 140 to 150 degrees Fahrenheit makes the milk taste sweeter. That velvety texture pushes the espresso’s crema around, which is what makes latte art possible.

Mixing coffee and milk is old. American writer William Dean Howells described a caffè latte on a steamship from Trieste to Venice in his 1867 Italian Journeys, but that was a proto latte. The modern drink waited for 1903, when the commercial espresso machine was patented with a steam wand that could aerate and heat milk at once. In Italy, milky coffees stay at breakfast, with straight espresso after 11 a.m. In the U.S., paper cups of 12, 16, and 20 ounces meant more milk, darker and more bitter espresso roasts to punch through it, and then sugar and syrups, turning a morning staple into an all-day sweet drink.

• Latte art requires dense microfoam that neither sinks nor floats passively like cappuccino foam.
• Hand whisking or heating milk on a stove cannot create a stable microemulsion.
• A latte macchiato reverses the build: milk and foam first, then espresso poured gently on top.
• The espresso in a latte macchiato settles in its own layer between the milk and the foam.
• American lattes are frequently sweetened with 3 percent or more sugar, artificial sweeteners, or agave syrup.