Answers to Student Questions
(from the articles)

Ice, Cream… and Chemistry

What is the function of air in ice cream?
By adding air to the ice cream mix, you increase the volume of the ice cream which, in turn, increases the time it takes for the flavor molecules to trigger the taste receptors in the mouth and tongue.
What is meant by the term “overrun”?
The term “overrun” refers to the amount of air in ice cream. If the volume of ice cream without air is doubled by adding air, then the overrun is listed as 100%, the maximum allowable in commercial ice cream.
What difference in the melting rate is caused by the amount of air in ice cream?
The more air in ice cream, the quicker it will melt. Higher quality ice creams contain less air than less expensive brands and therefore, melt more slowly.
What is the relationship between the amount of air in ice cream and its density?
The amount of air in ice cream is inversely related to its density: the more air that is present, the lower the density.
What is an emulsion? Explain how ice cream can be considered an emulsion.
An emulsion is “a combination of two liquids that don’t normally mix together. Instead, one of the liquids is dispersed throughout the other. In ice cream, liquid particles of fat—called fat globules—are spread throughout a mixture of water, sugar, and ice, along with air bubbles.”
Why is sugar added to the ice cream mix when the milk in ice cream already contains the sugar, lactose?
Sugar is added because, by itself, lactose does not taste as sweet as glucose or sucrose, the two types of sugar added to the ice cream mix. Further, the cold temperature of ice cream makes the taste buds less sensitive to the sweet taste. So, more sugar (glucose or sucrose) is added.
What percent of ice cream must be fat?
The percent of fat in ice cream must be a minimum of 10%. Premium ice cream may have up to 20%.
What is the purpose of fat in ice cream?
Fat in ice cream adds flavor and provides a velvety rich texture in the mouth. Reducing the fat content reduces the creamy texture sensation.
What steps must be taken to have the fat in ice cream mix with the other non-fat, water-based ingredients?
To ensure mixing of fat and non-fat ingredients, emulsifiers are added if they are not already in the ice cream in the form of milk proteins called casein and whey. These emulsifiers connect the fat molecules to the water-based ingredients which normally don’t mix.
What are some other emulsifiers in ice cream beside the milk proteins, casein and whey?
Some other emulsifiers added to ice cream include lecithin, mono- and diglycerides, and polysorbate 80.
What purpose is served by adding stabilizers to the ice cream mix?
The stabilizers added to ice cream prevent the formation of large ice crystals in the ice cream; they also slow the rate of melting.