How you prefer your frozen treats says a lot about a person. Are you dipping your extra-large, soft-serve cone in chocolate and sprinkles, stacking scoops of rocky road in a waffle cone, or delicately indulging in a cup of stracciatella gelato?
But no matter how you enjoy this summertime staple, there’s no doubt it’s born from a magical experience that transforms humble concoctions of cream and sugar into works of art. In other words, chemistry.
The chemistry of ice cream, soft serve, and gelato is a result of ingredients. These both ignite the process that leads to texture and variety and contributes to overall healthiness. However, if you’re looking for the “most healthy” treat, the answer has more to do with what ingredient you’d prefer to remove, rather than a clear favorite.
For chemists like Matt Hartings, an associate professor of chemistry at American University, understanding the science behind this icy treat only makes it better.
In addition to researching biological systems and anti-cancer drugs, Hartings also teaches AU’s “Chemistry of Cooking” course (aka, the science of ice cream). He tells Inverse the science-backed tips for making world-class ice cream right in your own home and explains why the same handful of ingredients, used in different measures, can result in a range of delicious options.
What is the science of ice cream?
First, names: In this article, we’re using “ice cream” as the encompassing term for gelato, soft serve, and “hard” ice cream (the ice cream you likely know best).
Modern ice cream shops will jam-pack their pints full of a wide array of mixins, from crushed Oreos to ripples of brown butter or pockets of jam. But in its simplest form, Hartings says that ice cream only requires four simple ingredients:
- Cream or milk (which contains both water and fat)
- And a stabilizer, like egg yolk or xanthan gum
Gelato — Italy’s ice cream — is creamier, silkier, and most elastic. This is because it uses more milk and sometimes uses egg yolks as the stabilizer.
Soft serve, meanwhile, is fluffier as a result of incorporating air during the internal freezing process (more on that later). It also uses less milk fat than typical ice cream.
Ultimately, and across the board, cream, sugar, and a stabilizer of your choice are mixed together and heated to form a liquid base for your ice cream, explains Hartings, and then whipped together with air at low temperatures (between 23 and 19.4 degrees Fahrenheit) and chilled to form something solid and scoopable.
Even though it’s not adding flavor or calories, air is the star of this process. You could think of it as being similar to making a meringue or whipped cream — without air, these toppings would be a wet mess.
But air is not the only ingredient responsible for this transformation, explains Hartings. He says that fat and protein in the mix also undergo a change through the base heating and freezing process.
“People do their Ph.D. thesis on this stuff,” says Hartings. “It's kind of wild what actually happens to the fat globules.
“If you think about what the fat looks like just floating around in milk it's just this tiny little contained balloon of liquid and as it freezes that liquid turns into a solid and when it does that it gets these spiky parts on it and that starts to interact with proteins in interesting ways,” he says.
Before the protein can interact with these spiky fat globs, however, it goes through its own glow-up during the heating process of a custard base.
“The egg proteins unravel [in heat] and then start grabbing hold of one another, making a sort of a mesh-like network inside of your cream and sugar base that you're using,” explains Hartings. “And that is in the end, what makes your ice cream creamy.”
What ice cream is healthiest?
This comes back to ingredients. The chemistry between these ingredients is what leads to the differences between treats like ice cream, gelato, and soft serve.
If you want lower amounts of certain ingredients — in other words, less milk and sugar — then you might want to go with soft-serve or gelato. Gelato contains less butterfat and less sugar compared to typical ice cream, while soft-serve includes less milk fat than typical ice cream.
Comparing calories, meanwhile, is an inaccurate process because there are so many varieties of regular ice cream to choose from. Soft-serve might feel lighter as a treat because it literally is — a fact that goes back to air. Air, research shows, leads to less creamy products.
How to make ice cream extra creamy
Even with the highest quality ingredients and beautifully aerated ice cream, you might still find that your final product has an unpleasant icy crunch when you sit down to enjoy it.
This has to do with another ingredient, Hartings says: time.
“The longer it takes to freeze your ice cream, the bigger your ice crystals are going to be,” says Hartings. “If you can shorten the time it takes to freeze, you're going to have a creamier, less gritty ice cream.”
One way to do this in a chemistry lab or commercial kitchen — though, probably not at home — is by rapidly cooling down your churned ice cream using liquid nitrogen. This brings the ice cream’s temperature down without leaving much time for ice crystals to form, Hartings explains.
But if you’re looking for extra creamy ice cream — like a gelato — Hartings says you may need to tweak a few other parts of this basic ingredient list. Unlike hard ice creams, which can be filled with up to 50 percent air, gelato is less aerated. Soft serve, meanwhile, is mostly air: You can think of it as melted ice cream whipped up with air.
“The higher the temperature, the sweeter the sugar will taste.”
Gelato in particular also typically has lower fat content than ice cream because it uses more milk than cream. Combining this with warmer freezing temperatures and slightly less sugar makes for a super creamy treat with flavors that pack a bit more punch, Hartings explains.
“The higher the temperature, the sweeter the sugar will taste,” he says. “So if you use the same amount of sugar in your gelato as say you do in an ice cream, that is going to be a super sweet gelato.”
As a result, sugar and flavor go further in the Italian treat.
As for soft serve, Hartings says that watching the thick swirl unfurl from a machine truly is chemical magic. Without a need for churning, cooling tubes on the soft serve machine itself work to semi-solidify the liquid base and inject air.
Tips for making your own ice cream
Armed with your new chemistry knowledge, Hartings has a few tips for aspiring ice cream makers who want to try making the sweet stuff at home. When it comes to flavor, Hartings recommends getting creative with how you flavor your base.
“My favorite ice cream, both that I make at home and that I can get when I go out if I know they make it well, is coconut,” he says. “I always toast my coconut first and then I steep that in the base that I'm making — the toasted coconut flavors are just awesome.”
Another tip for achieving ultra-creamy ice cream is to perfect how you heat your liquid base. For custard-based ice creams that use egg yolk as a stabilizer, Hartings says you want to cook your mix low and slow until it reaches about 170 degrees Fahrenheit.
But if that you’re still struggling with a scrambled base or icy ice cream, Hartings says there’s no harm or shame in using a stabilizer like xanthan gum instead of traditional egg yolk. Made from fermented sugar, this stabilizer can now be found at grocery stores sold by brands like “Bob’s Red Hill.”
“You'd be better off using some of these other stabilizers, like xanthan gum,” says Hartings. “You don't have to get to control the temperature so much, so they are technically very easy to use.”
“People tend to worry about some of the other stabilizers and think ‘oh it’s a chemical additive’,” Hartings continues. “To put that to rest, a lot of the additives that do get used are made by organisms. They come from nature.”
But ultimately, no matter how you churn, scoop, or lick it, any ice cream you make is going to be scientifically delicious.
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