In broad strokes, we all know that gelato is denser and richer than American ice cream. Its flavor is intense and it forms swirly folds rather than pert round scoops. But what does that really mean, and how does it happen? There are three big factors at work:
American ice cream has way more butterfat—that is, fat from cream and milk—than gelato. Legally speaking, the FDA requires ice cream to be at least 10% by weight to be labeled as ice cream. Super premium ice cream brands climb as high as 16%, and home recipes—which rely on less efficient machines that require more texture insurance—can climb above 20%. By comparison, Italian law requires gelato contain a mere 3.5% butterfat. It can go higher than that, but doesn't need to.
Cold fat tastes like pretty much...nothing. It coats and dulls the tongue, impeding the sensation of flavor. Since gelato's so light in fat, it tastes more intense. The flavor hits you first, not the dairy.
Butterfat also affects texture; the more butterfat an ice cream mix contains, the more air it's able to absorb during churning, which translates into a billowy scoop that holds its shape and, paradoxically, registers in the mouth as super light. (Consider the light-as-air texture of whipped cream compared to the coarser froth on a carton of shaken milk.)
Since gelato's so light in fat, it doesn't suck in much air during the churning process. American ice cream can double in volume during churning, ballooning up with air. Gelato's overrun, in ice cream speak, is much lower, resulting in an ice cream that feels more dense and rich—because it is. But since that richness is less dependent on fat, gelato melts fast and clean on the tongue.
When you order a scoop from an ice cream shop, it's likely sitting in a service freezer that hovers around 0 to -10 degrees Fahrenheit, the temperature at which hard-pack American ice cream is scoopable but keeps its shape.
Gelato's served much warmer—a good 10 to 20 degrees—which helps keep it soft and dreamy despite its lower butterfat. Cold also dulls the tongue, and gelato's warmer serving temperature makes its flavor that much more immediate and aromatic.
The result? A scoop that's potent and pure-tasting and dense but not heavy.