Contrary to what you may have heard, fat is good.
One of the biggest factors in ice cream’s texture is the amount of “butterfat” (the fatty part of milk) that it contains. If there’s not enough butterfat, the ice cream tends to taste icy and not very smooth—which is fine if you’re making a sherbet or a sorbet, but not great if you’re aiming for your own version of Ben & Jerry’s. On the other hand, if there’s too much butterfat, it starts to taste greasy like lard, and it sticks to the inside of your mouth. Or in other words, it has bad “mouth feel”.
Another big factor that controls the texture is the amount of air in the ice cream. Companies with big fancy machines can control the amount of air they introduce into the ice cream, and adjust the mouth feel that way as well. But since our home machines add a fairly fixed amount of air each time, our main method of controlling the texture is by controlling the butterfat content.
- Homemade ice cream recipes often contain about 19% butterfat. See my post about Making an Ice Cream Butterfat Calculator  for more info.
- Super-premium ice cream contains about 14-16% butterfat.
- Premium ice cream like Ben & Jerry’s and Häagen-Dazs is probably in the 12-14% neighborhood.
- Ice cream in the U.S. has to contain at least 10% butterfat and less than 1.4% egg yolks, according to the FDA’s regulations .
- Frozen custard is similar to ice cream, and is defined by the same FDA regulation as ice cream. It also must contain at least 10% butterfat, but must also have at least 1.4% egg yolks. It’s made with a machine that adds less air so it tastes more dense, and it’s served fresh at a higher temperature so it’s usually softer.
- Gelato isn’t regulated in the U.S., but is usually about 3-8% butterfat and often contains more stabilizers  to compensate for a lack of cream and eggs. And like frozen custard, it’s also made with less air, and served warmer, than ice cream.
- Soft Serve is often around 3-6% butterfat. Dairy Queen, for example, is 5%.
- Ice Milk is about 3.5% butterfat, the same as whole milk.
- Sherbet is also defined by the same regulation as ice cream in the U.S., and must contain 1-2% butterfat.
- Sorbet usually contains no dairy at all, and is usually just frozen fruit juice, sugar, and water (and a great alternative for people that can’t eat dairy).
The percentages of butterfat listed above are by weight, not by volume. So if you took a gallon of 16% super-premium ice cream and pumped it full of enough air to make it into two gallons, it’d still be 16% butterfat by weight, but it’d taste entirely different (and terrible, probably). When you eat a super-cheap grocery store ice cream that tastes like you’re eating flavored air, that’s pretty much what it is. They’ve put too much air into it, so they can sell more of it without actually adding more dairy ingredients. Of course, the opposite can happen as well. If there’s not enough air in the ice cream, it tastes too dense, almost like a frozen block of cream. There’s a fine line between too much or too little air, and too much or too little butterfat.
The increase in volume of ice cream from adding air is referred to as overrun, and is calculated as a percentage of the original product. So if you started with a gallon of ice cream base and added the same amount of air to double it, it’d have a 100% overrun, which also happens to be the maximum allowed in the U.S. Some countries allow a maximum of 120% overrun.
Gelato and frozen custard are usually sold fresh, meaning they’re not stored like ice cream in a deep-freeze until they harden. This is partly because the butterfat content is low enough that the water in the mix would freeze into larger crystals, making it taste icy.
Most ice cream recipes I’ve seen use heavy whipping cream, light cream, milk, or half-and-half. The recipe I mentioned for the Sweet Cream Base  uses 2 cups heavy whipping cream and 1 cup whole milk. Most of the butterfat comes from the cream, and the milk is mostly just to increase the volume. You could even use skim milk if you wanted, and then just increase the cream a bit to compensate for the lost butterfat. Or use half-and-half with less cream. That particular 2-to-1 ratio is just the one Ben & Jerry’s picked because it’s easy to make and it comes out to the amount of butterfat they wanted, which if I calculated correctly , is about 19%.
- Heavy whipping cream is about 36% butterfat, and is not the same thing as “whipping cream” (which is 30-36%). In Australia I believe it’s called “pure cream”, although you can also get “thickened cream”, which has gelatin added to raise the viscosity and make it easier to whip. In the UK it’s called “whipping cream”.
- Light cream is about 20% butterfat. I believe it’s “light cream” in Oz and “single cream” in the UK.
- Half-and-half is typically about 12% butterfat, but can be between 10.5 and 18%. It’s made from a 50/50 mix of light cream and milk. If you wanted to make your own half-and-half from heavy whipping cream and milk, I calculate that you’d need to use about one part heavy whipping cream to three parts whole milk. But 12% is the number that’s important, and the fact that it has about a third the butterfat of heavy whipping cream. I believe half-and-half is called “half cream” in Australia and the UK.
- Whole milk is usually around 3.5% butterfat. Or in other words, about a tenth of the butterfat in heavy whipping cream.
- Skim milk has less than 0.5% butterfat.
Whole milk is what recipes usually mean when they say just “milk”. It has basically the same butterfat as raw milk straight from the cow. If you let raw milk sit for a while, it separates into milk and cream, which rises to the top. If you “skim” off the cream, you’re left with skim milk. If you add more cream to it, you get the creams listed above, with heavy whipping cream being pretty close to pure cream. If you mix the cream and milk together real well and basically smash all the little fat globules together, it’s homogenized, and won’t separate anymore. If you heat the milk to a specific temperature for a specific amount of time, it’s pasteurized, and won’t contain bacteria like salmonella  anymore.
By the way, ever wondered what 2% milk is two percent of? Well, it’s not 2% of the butterfat in whole milk, because that’d be 2% of 3.5%, or in other words, white water. :-) It’s 2% total butterfat, just like whole milk is 3.5% total butterfat. 2% milk is about 5 grams of fat per cup (240 ml) compared to 8 grams per cup in whole milk. Drink up.