Cool Chemistry: Stretchy Ice Cream

In addition, because the process may be as important as the ingredients, the group has tried stirring their ice cream with anything available: a spade used to dig up dandelions, a restaurant-quality mixer and even an electric drill with a flat bit. The mixer eventually won, along with a lot of old-fashioned elbow grease.

To make a fresh batch, the lab group heats milk and adds the ingredients at different temperatures. After boiling, the thickening mixture is beaten in the mixer and then stirred by hand for at least 30 long and fatiguing minutes in a canister surrounded by dry ice, crushed ice and salt. The freezing process continues in a freezer overnight. When the group pulls it out of the freezer the next day, the ice cream is a solid block that has to soften before it can be pulled and beaten to the desired stretchiness.

Johnson describes the final product as “cold like ice cream, but with a lot more elasticity.” A glob on the tongue won’t melt as uniformly as other ice cream; the inside remains frozen, even as the outside turns to something barely thicker than cream. It’s basically ice cream you can chew.

In the future, the group hopes to actually quantify the stretchiness using precise machines, such as a rheometer to measure the ice cream’s viscosity, or resistance to flow. And in the coming months, they will begin testing a possible substitute for salep. While orchids are common in the Mediterranean region, some species are rare and are sometimes harvested along with the abundant ones.

“I think that it is quite a serious conservation problem,” says Andrew Byfield, a landscape conservation manager at the British conservation charity Plantlife International, who has lived and worked in Turkey. Trade restrictions apply to all orchid varieties, making one of the ice cream’s crucial ingredients hard to obtain in the United States.

Kirshenbaum says he might have a good stand-in for these little orange-ish orchid roots that are slightly shriveled before they’re ground. It’s called konjac flour, used in some Japanese noodles and gelatinous Japanese candy. Ronald Kaufmann, an associate professor of marine science and environmental studies at the University of San Diego who sits on the boards of several orchid organizations, says of the candy’s springiness: “You bite into it, and it bites back with a vengeance.”

Konjac flour is made from a plant called Amorphophallus konjac. Kaufmann says this plant can be six feet tall and “smells like a garlicky, decomposing elephant”—not at all like most orchids. One thing that salep and konjac do have in common, though, says Kirshenbaum, is that they contain the polymers called glucomannans. So, again, it makes sense that these polymers give the ice cream its entertaining stretchiness.

“It’s all totally consistent with polymer science,” Kirshenbaum says.

However, some people from Turkey may be reluctant to give up salep, an alleged aphrodisiac. In fact, the word “salep” means “fox testicles,” apparently because of the way the orchid roots look. Harold Koopowitz, a retired ecology professor from the University of California at Irvine who is involved with multiple orchid societies, says that some people believe salep has medicinal properties. They make a hot drink with it in Turkey, he says, like the chicken soup made here in the United States.

But for now, it’s back to the mixing bowl in the group’s new workspace in the food studies department. Here, Kirshenbaum and the students enjoy an intimate relationship between science and food. As Silver, one of the students, puts it: “It’s cool. It’s definitely chemistry.”

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