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Press play to hear Banger's explanation of freezing-point depression.
Try the activities below for more about physical and chemical changes in cooking
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Ice cream is an excellent example of the whole tasting better than the sum of its parts.
According to legend, the Roman emperor, Nero, was the first person to make ice cream. He ordered slaves to bring snow from the Alps, which was used to freeze a flavoured cream mixture. The secret was to lower the freezing point of ice in order to freeze the cream mix. Notice that ice cream melts differently than ice. Ice stays hard until it melts; but ice cream gradually get softer and softer. Ice is a pure substance but ice cream is a mixture. In other words, there are other chemicals that get in the way of ice freezing. So you have get colder than 0°C to get it to freeze. About 30% of the water in ice cream never freezes because of the high level of dissolved solids like sugar, fats, and proteins. How? The scientific secret is salt! From a physical chemistry perspective, ice cream has a colloidal structure: tiny air bubbles and ice crystals are dispersed among liquid water and a network of fat globules. This structure contributes to how the flavour is released into your mouth. Similar foods with a colloidal structure include milk, butter, jelly, marshmallow and many more.
Ice crystal size and freezing rate also affect the texture and flavour of the ice cream. For a smooth consistency, ice crystals should be small: large crystals give a coarse, grainy texture. Slow freezing creates a small number of large crystals, whereas fast freezing promotes a larger number of small crystals- which is what you want in really good ice cream. In addition to getting the mix to freeze, there are other reactions and processes involved in making ice cream. Ice cream consists of:
Also, by volume, approximately 35% of ice cream is air, whipped into the mix during the early stages of the freezing process. This interactive animation demonstrates freezing-point depression: Visit this site to find out more.
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