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Compare eating a popsicle, scoop of vanilla ice cream, and a slice of semifreddo. They are pretty different in texture. A popsicle is hard, a scoop of vanilla ice cream is softer and can be scooped, a semifreddo is even lighter and airier.
One of the main differences between these styles of ice cream is the amount of air they contain. Yes, air, pretty much like the air around you. A lot of ice cream styles contain air. Air is crucial to ensure you can scoop many ice creams, but it also makes ice creams taste warmer. Sound contradictory? We’re going to explain it all.
Your ice cream pints can be 50% air, for a reason
Next time you buy a pack of ice cream, weigh it. Eat it and then fill that pack with the same amount of water. Probably, your ice cream pack full of water is a lot heavier than that same pack filled with ice cream.
Why? Because most ice creams contain a lot of air. In store-bought ice cream, half of the ice cream’s volume may be made up of air. It’s why a 1-liter carton of ice cream may only weigh 500g, whereas that same carton filled with ice cream weighs 1000g when filled with water.
Yes, ice cream manufacturers are literally selling you air. But, they don’t just do this to save money, since air is cheap. Air plays some very beneficial and crucial roles in ice cream.
Air improves scoopability
Ever tried scooping a popsicle? Probably not, they tend to be too hard to scoop. One of the reasons it’s hard to scoop popsicles is their lack of air. They are pretty much dense frozen sugar solutions full of ice crystals. It is very hard to scoop into an ice crystal. However, it’s not that hard to scoop through an air bubble. If your ice cream contains a lot of tiny air bubbles spread throughout, these make it a lot easier to scoop through.
Air insulates your tongue
Some ice creams just feel a lot colder when you eat them than others. Despite both of them coming from the exact same freezer. Compare popping a solid ice cube in your mouth vs. a scoop of gelato. Again, air plays a key role here.
Frozen ice cream contains a lot of ice crystals. When these ice crystals touch your tongue they melt. To do so, they extract heat from their surroundings, making you feel the cold. If your whole tongue is covered with a smooth sheet of ice crystals, that would be pretty cold. However, if that sheet now contains a lot of air bubbles, not all those ice crystals will be able to touch your tongue. Instead, the air serves as an insulating layer between your tongue and the ice.
Air bubbles serve as an insulator, making an ice cream seem less cold.
How to incorporate air into ice cream
Air clearly serves a purpose, but how do you incorporate it into your ice cream? You can do so in a few ways:
- Incorporate air into an ingredient that can hold onto air well
- Heavy cream
- Incorporate air while freezing the ice cream
Whisk cream or eggs
Whisk some cream or eggs and within a few minutes you’ll have a light and airy foam. Both ingredients are great at holding onto air if you force air in using a whisk or mixer. Simply fold in the other ingredients, and you’ve got an ice cream base, ready to be frozen.
In cream, it’s the fat molecules that make it great at holding onto air. The fats organize themselves around the air bubbles, stabilizing them. We use it to make a simple 2-ingredient ice cream. In the case of eggs, it’s the proteins that excel at holding onto air bubbles. We use those to make a light and airy semifreddo.
Cream nor eggs can hold onto air forever though. Over time, they’ll slowly collapse, deflate, into a puddle. But, they don’t need to either. Once the ice cream is frozen, it becomes so firm that the air bubbles are locked in place.
Freeze & mix
It isn’t always possible to use an ingredient to hold onto the air. Also, ice creams made that way tend to be a little less stable over time. You can’t store them for as long.
In these instances, you’ll have to incorporate the air while freezing the ice cream. During freezing the ice cream becomes firmer, making it harder for air to escape. There’s a sweet spot during this process where the ice cream is not yet too solid to be mixed, but firm enough to hold onto the air.
This is what ice cream machines do in a process called churning. The machine both freezes and mixes the ice cream simultaneously. If you don’t have an ice cream machine, you can also do this by freezing an ice cream base and taking it out of the freezer at regular intervals, stirring it, to incorporate air.
In ice cream factories they use more advanced equipment, but the principles are pretty much the same to those you use at home. Learn more about factory-scale production here.
Thicker ice cream bases = More air?
Custard-based ice creams are a style of ice cream in which you first make a thickened custard, which you’ll then churn. One of the reasons an ice cream base like this works so well is that its increased viscosity (it’s thicker), helps it hold onto air during churning.
Air is just one of the components that makes your ice cream a success. Want to learn all about the science of ice cream? Why not take our 4-week ice cream course? Not yet ready for a course, scroll through our ice cream archives. I’d suggest learning more about the freezing point depression or the role of emulsifiers next!
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