Ice cream may seem like a simple treat, but achieving the perfect creamy texture requires a careful balance of chemistry and the three states of matter: solid, liquid, and gas.
Commercial ice cream contains a variety of ingredients including air, water, milk fat, milk solids, sweeteners, stabilizers, emulsifiers, and flavors. These ingredients are mixed and pasteurized for safety. Homemade ice cream typically consists of milk, heavy cream, sugar, and flavorings such as fruit or chocolate.
When the ice cream mixture is cooled, small clusters of water molecules form tiny ice crystals. The size of these crystals determines the smoothness of the ice cream. To ensure small ice crystals, ice cream makers agitate or beat the liquid as it freezes. Mixing also incorporates air, which gives ice cream a lighter texture.
The fat in milk exists as globules surrounded by proteins. These proteins help keep the fats suspended in the mixture. Homogenization breaks down large fat globules into smaller ones, ensuring even freezing and preventing fats from sticking to the machinery. Freezing the fat globules causes them to clump together, creating a creamy texture.
Sugar and other dissolved ingredients in milk also play a crucial role in the texture of ice cream. The presence of sugars lowers the freezing temperature of the mixture. As ice crystals form, the concentration of sugars increases, further lowering the freezing point. This concentrated liquid, known as the “serum,” bridges between the ice crystals, fat globules, and air bubbles, adding flexibility to the mixture.
Not all frozen desserts can be legally called ice cream due to regulations governing milk fat content. Variations like gelato and sorbets have different ingredients and proportions but undergo similar steps of ice crystal formation, fat solidification, and serum phase separation.
Soft serve products contain less air than traditional tub ice cream due to constant agitation during freezing. “Water ices” like icy poles or freeze pops are frozen in molds or plastic tubing without stirring, resulting in less controlled ice crystal formation.
Ice cream has been enjoyed for centuries and offers endless flavor variations. It evokes feelings of happiness, comfort, indulgence, and nostalgia, all while involving plenty of chemistry.