Ice cream isn’t gelato because of additional air, fat and cold
My third-grader said she has a preference for ice cream over gelato, which is interesting since they’re nearly the same mix of sugar, fat, ice and air. Gelato actually means ice cream in Italy, but the rise of what some people call “American ice cream” has prompted some examination of the differences between the two desserts, even beyond third-graders. The same flavoring may seem to taste a bit different, despite similar ingredients. The key is how the frozen treats are prepared, and the specific balance of fat, temperature and ice you’ll find in each.
Ice fixed with fat
At their core, ice cream and gelato both share the same basic formula. By volume, each sugary scoop is mostly ice, but that ice has been prepared to keep it from behaving like a hard, solid block in your mouth. Through a process known as emulsification, the ice crystals are kept as small and separated as possible so that no single piece of ice stands out. They’re suspended between milk fat, sugar and in the case of custard-based ice creams, egg yolk proteins which makes for a cold but smooth and creamy texture, rather than something as hard and crunchy as a snow cone.
Getting the fat and ice balance right is a big part of what makes ice cream delicious. Richer ice creams tend to have more fat, and products labeled “ice cream” in the United States are even required to be at least ten percent fat. Gelato, on the other hand, is made with more milk than cream, and so it has less fat per serving.
Inflated with air
To further soften the fat and ice, air is also whipped into both ice cream and gelato. Ice cream has air whipped in more vigorously, leaving more air bubbles trapped inside the fat, ice and sugar and increasing the volume of the finished product. That change in volume due to air is called overrun, and it can vary a lot depending on the recipe being used. Premium ice creams tend to avoid adding more than 25 percent overrun since it means less fat, sugar and flavor per scoop, but cheaper ice creams really fluffs things up. At the far end of the spectrum, soft-serve ice cream can have 100 percent overrun, making for a very spongy dessert that can melt pretty quickly.
Again, gelato follows the same formula, but in different amounts. Gelato overrun amounts are generally much lower, as it’s churned more slowly than other ice creams. The result is a denser scoop that can pack a lot of flavorings (versus air) into each bite. With less cream and less air, it seems like gelato should be getting closer to just freezing into a single block of ice, but that’s where temperature comes into play.
Ice cream is produced and stored at lower temperatures than gelato. Commercial ice cream is sometimes churned in drums cooled with ammonia to -22° Fahrenheit, which helps keep the emulsified ice from moving around too much. It’s generally served at around 10° Fahrenheit so that it’s cold enough be structurally stable while starting to soften enough to let the tasty fats and sugars interact with your tongue.
Gelato avoids freezing up by being churned and served at higher temperatures. Even though there’s less fat, no egg yolks and less air to keep the ice from congealing, the warmer temperatures help maintain the pleasant, creamy texture. It can get soupy pretty quickly, although both gelato and ice cream recipes often include various gums or gelatin to help keep the structure stabilized.
Sugar and salts are of course two more important ingredients for these frozen treats, but they vary so much by recipe that they’re not useful to differentiate ice cream from gelato. Both help keep ice crystals separated while lowering the water’s initial freezing point, but the amount of sweet or salty is usually more about the desired taste rather than the defining the exact amount of creaminess. Perhaps the sweetness does play another role though, which is to add to one’s motivation to finish dessert before finding out when their ice cream or gelato is going to fall apart.
Source: What's the Difference Between Gelato and Ice Cream? by Max Falkowitz, Serious Eats