Ask Dr. Universe – Ice Cream

How is ice cream made? –Israel, 7

Dear Israel,

It just so happens that July is National Ice Cream Month. To celebrate, I decided to whip up some homemade ice cream. You can try it at home, too.

Put milk, sugar, and vanilla into a freezer bag and seal it up tight. Fill another gallon freezer bag with ice and rock salt. Place the liquid mix bag inside the ice bag and give it a good long shake. Some scientists might call this part “agitating.” After five minutes or so, you’ll notice the liquid mix in your bag becomes solid. Then you can dig in with a spoon. Find all the instructions for Ice Cream-in-a-Bag at

After making my own homemade tuna-flavored ice cream, I decided to take a trip to the Washington State University Creamery to see how the professionals make ice cream for Ferdinand’s Ice Cream Shoppe.

I met up with our friend John Haugen, the creamery manager. Each year at the WSU creamery, students make more than 18,000 gallons of ice cream. That’s a lot of scoops.

Just like our Ice Cream-in-a-Bag recipe, their recipe uses a mix of milk, cream, and sugar that’s frozen in a way to prevent crystals from forming and incorporates enough air to make it soft. At the creamery, milk flows through pipes into big stainless steel tanks that have been specially engineered.

The students add a bit of fat to the mix in the form of cream, which gives the ice cream a smooth texture. When the fat mixes with air, it helps create small pockets in the ice cream. It makes the texture smoother. In fact, a scoop of ice cream is about half air.

When making ice cream, we need to keep the ingredients blended together. With all the liquids going in the vat, we also add a few solids like dry milk, followed by the sugar. Then, we heat it up to 155 degrees to pasteurize the milk and kill any bad bacteria that might have snuck into the mix.

We also don’t want the cream to rise to the top or different parts to separate. This is where we add in what’s called an emulsifier. One of the original emulsifiers that did the trick was actually egg.

We also want to keep the ice cream from getting too many ice crystals. So, we add in a bit of carrageenan, a kind of seaweed. But it’s just a tiny bit. It helps keep the ice cream from forming those tiny ice crystals.

The liquid goes through a homogenizer, forcing the mix through a small opening and breaking down milk fats into smaller pieces to make the ice cream even smoother.

Finally, the mix goes through a specially engineered machine to bring the temperature down. Then it gets sent through a freezing barrel and packed into boxes until it’s ready to eat. The best part of the job is eating the ice cream, Haugen adds.

Sometimes there’s no better way to find out how something is made than to give it a try. Tell me about your ice cream experiments sometime at

Dr. Universe

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