National Ice Cream Month, recipes
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The Science of Ice Cream

Muffie Fulton is the founder and creative head of Bold Food, which offers classes in the science of cooking and modernist cuisine, as well as curated culinary tours all over the planet.  Join her at Feastly SF for some modernist pop-ups!

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Ice Cream College

Just about everyone loves cold, sweet, and creamy ice cream. I’ve done quite a lot of ice cream reading and making. But when I wanted to learn as much as possible about it, I decided to go to ice cream college, or more specifically, the famous (in ice cream circles, anyway) Ice Cream Short Course at Penn State University. Every January for the last 126 years, over a hundred people gather to learn just about everything there is to know about ice cream.

What defines ice cream?

Scientifically, ice cream is a partially-frozen emulsion of fat, sugar, protein, and air in water. Sounds delicious, doesn’t it? Believe it or not, the U.S. has a legal definition, and the FDA specifics which frozen desserts are allowed to be called “ice cream” so you know what you’re buying. How much milk fat and protein, the minimum weight of a gallon, its pasteurization, freezing methods, sweetening, and flavors are all part of the ice cream definition. But this definition doesn’t say a whole lot about what it actually is. There are seven main components: water, milk fat, milk proteins, sugar, air, stabilizers, and emulsifiers. Each ingredient has a specific purpose and amount.

Water

Coming from milk and cream, water is the most abundant ice cream ingredient and makes up 60-65% of the total weight. Everything in the ice cream is either dissolved or suspended in water, with much of the texture determined by the ratio of liquid to frozen water.

Milk Fat

Milk fat adds flavor and texture while contributing to the cold sensation you get while eating ice cream. The percentage ranges from 10-20%. As it is the most expensive ingredient, it is the main element that defines an ice cream’s quality. Premium brands like Häagen Dazs or Jeni’s will have 16-20% milk fat, while store brands will likely have only 10%, the minimum required by the FDA (unless the package specifics low-fat). 

Milk Proteins

8-12% of ice cream’s weight comes from milk proteins, which add flavor and powerful emulsification. They coat both the fat droplets and the air pockets, allowing them to be dispersed in the water. If you’ve ever had ice cream that leaves a greasy feeling in your mouth, it could be that there weren’t enough milk proteins to ensure fat droplets stay small and dispersed. The ice cream could also have been over-churned, which physically strips the proteins from the fat. This allows them to coagulate and make globules large enough to feel in your mouth.

Sugar

Sugar is another important ingredient, making up 12-20% of the ice cream’s total weight. Beyond the obvious sweet flavor it provides, sugar is also essential in depressing the freezing point and allows the ice cream to have a freezing range. Pure water has a freezing point, which  means at 33 degrees Fahrenheit it is liquid but at 32 degrees it is solid. Ice cream should not be either liquid or solid, which means it should have a freezing range a few degrees above or below the temperature at which we would like to eat it. Good ice cream will be the proper ratio of liquid water to solid ice.

Air

Air is ice cream’s cheapest ingredient, but it is no less important. Ice cream is agitated while being frozen, which incorporates air. The amount of air in ice cream is called “overrun.” Proteins and added emulsifiers coat air bubbles and help them stay dispersed. Lower quality ice creams have more air, sometimes 100% overrun, meaning that air takes up half the volume. Higher quality, higher fat ice creams incorporate less air and are denser, with overrun as low as 20%.

Stabilizers and Emulsifiers

Stabilizers and emulsifiers (SEs) are currently rather controversial ingredients among consumers. Even though the popular press often touts SEs as dangerous and added by big companies to make money, they are completely safe — most are isolated from plants like seaweed or soybeans. They’re also critical to making high-quality ice cream. The amount of fat and air incorporated into the ice cream plays a very important role in the texture and “scoopability.” Without them, you either get a soupy mess or a block of ice. SEs help coat fat globules and air pockets to keep them in suspension.

They also help control the water and ice. Smooth ice cream has tiny crystals that are too small to feel in your mouth. As the ice cream’s temperature fluctuates during shipping, purchase, and storage (yes, even in your freezer), some amount of the ice cream melts and refreezes, making larger ice crystals. You may have experienced this when tasting a forgotten (and potentially crunchy) pint of ice cream from the back of the freezer.

SEs actually help bind the water and ice crystals, separating them and limiting the crystal growth during thawing and refreezing. This helps maintain a soft texture and allows cold ice cream to be soft enough to eat with a pleasant mouthfeel. Häagen Dazs, for example, makes very high-quality and tasty ice cream. A major selling point is that they do not use SEs (only five ingredients). However, when you take it out of the freezer to eat, it’s very difficult to scoop!

What now?

With this knowledge, you can evaluate different ice cream brands based on what is important to you. Do you like rich, firm, and creamy ice creams? Or do you like fluffy, lighter ice creams that remind you of your childhood and are perfect for scooping into cones? Moral of the story: you may want to think about these components and look beyond flavor as the main method for choosing your ice cream…or you can make your own! Check out my recipe for sous vide, liquid nitrogen ice cream here.


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