Ice Cream Delight

Most of us have made ice cream or seen ice cream being made. Milk, eggs, sugar, and flavorings are slowly chilled. Terri likes to make ice cream in a simpler and more efficient way. Practicing proper safety precautions, she pours liquid nitrogen directly into the ingredients in a metal bowl. About equal volumes of liquid nitrogen and the mixture are used for ice cream or sorbet, and she stirs while adding the coolant until the ice cream is nicely stiff. Why does this method produce absolutely marvelous ice cream, and what is the physics here?

Answer

Good ice cream contains abundant air bubbles to keep it light with very small ice crystals so that the texture is smooth. There are several good small appliances for making ice cream and sorbet. Some ice cream makers rely on human muscle power to turn a large spatula to control the ice cream texture; others are electric. But with an abundant supply of liquid nitrogen at –196°C and about an equal volume of ice cream mixture, the freezing of the ice cream occurs so fast that only small crystals have time to grow. As the nitrogen furiously boils, plenty of small gas bubbles form in the mixture. All these effects make for a delicious treat.