Instant Ice Cream

Liquid nitrogen is the not-so-secret ingredient an engineering professor uses to make frozen treats for guests

One day every April, Tom Vandervelde, an associate professor of electrical and computer engineering, sets aside prep for classes and his research on renewable energy, and focuses on the lighter side of science: he makes instant ice cream. All he needs, in addition to a stand mixer, are half-and-half, heavy cream, sugar, and a special ingredient: liquid nitrogen—LN2 in the lingo—which causes rapid freezing on contact.

Ice cream day started ten years ago, when elementary school groups would tour his lab. “At the end of their visit, we would make LN2 ice cream as a treat for them,” Vandervelde said, impressing them with the powers of science. He and his students kept it simple for the kids—the choice was either vanilla or cookies-and-cream—but soon decided they’d like some ice cream themselves, and a bit more daring flavors.

On April 19, about fifty people dropped by the Renewable Energy and Applied Photonics Lab for this year’s celebration, with a dozen flavor choices that ranged from chocolate espresso and horchata to Lucky Charms and lemon ice box pie.

Freshly made ice cream, plus fog from the instant chill of the liquid nitrogen. Photo: Alonso NicholsFreshly made ice cream, plus fog from the instant chill of the liquid nitrogen. Photo: Alonso Nichols

There’s certainly no waiting around for the ice cream to set. “The simplest ice creams are just mixing half-and-half and heavy cream with sugar and vanilla in a mixer, then slowly pouring in LN2, which turns it into ice cream in about three to five minutes,” Vandervelde said. “For most of the fancier flavors, we have to make a custard base the night before and add flavors as it is cooling.” Technically, he said, most of the recipes are frozen custards or gelato, rather than ice cream, “but we don’t keep track.”

The customers, of course, were happy, and suggested Vandervelde should open a stand and sell his ice cream, “but I don’t think that is going to happen,” he said. “We might have a stand and give it away for Community Day—we’ll have to see.”

And Vandervelde’s favorite ice cream? He talks about visiting a gelato shop in Freiburg im Breisgau in Germany, when he was on sabbatical there. “My kids loved the Schlumpfe—Smurf—flavor ice cream. It tastes like blue moon ice cream, which is popular in the Midwest,” he said. “I really enjoyed their honey pine nut, but the jogurt mit cayenne was my favorite. It is a sweet, yet tangy, Greek yogurt flavored gelato with cayenne added to give it some heat—it is perfection.” Will it be on tap for his ice cream fans next year? Maybe, he said. “I have not been able to replicate it here . . . yet.”

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