In a healthful diet, ice cream definitely falls in the “once in a while” category. The process that creates this highly regarded treat is fascinating. Even a basic understanding may help you appreciate the indulgence more when “once in a while” rolls round.
X-Ray Vision If asked to name the ingredients in ice cream, you might say “cream, milk, sugar, and eggs.” A food scientist might say “fats, milk solids, sweeteners, emulsifiers, and stabilizers.” Moreover, the scientist might add that ice cream is a foam and an emulsion.
This approach—looking past the foods and into their functions—is a good way to understand ice cream’s complex inner life. The ingredients in ice cream play roles that are similar to their purposes in baked goods. Because they are frozen rather than baked, heat is removed, not added. They don’t react chemically with each other, yet they still work together. Each one influences the effects of the others.
Fats. Fats provide a rich, buttery “mouthfeel” to ice cream, even more than they do in baked goods. They bind to aroma-carrying compounds to spread flavor. They also hold air when whipped.
In freezing, fat serves another function. Ice cream is about 50 percent water by weight. As water freezes into ice crystals, a pleasing degree of firmness results. Large crystals feel gritty, however. Fat globules coat the ice crystals, limiting their growth.
As you may have guessed, cream—specifically, butterfat—is the main source of fats in ice cream. Like other fats, butterfat melts over a narrow range of temperatures, not all at once, which helps produce a pleasantly gradual “meltdown” in the mouth. This too gives the sensation of smoothness.
Milk solids. Milk solids include proteins and minerals. You may recall that proteins build foams by trapping air, as in meringues and soufflés. In this way, they aid the action of fats. At the same time, proteins surround fat globules in a thin membrane. This keeps them from combining into larger globules and making the ice cream taste “fatty.” Meanwhile, minerals like calcium and magnesium help control ice crystallization. Milk solids may be added dry or in whole or sweetened condensed milk.
Sweeteners. Besides sweetness, sugars soften ice cream’s consistency. As sugars dissolve in the water, they lower its freezing point. Some water never freezes, which keeps the ice cream from hardening completely. Honey and corn syrup, which have a simpler structure than sucrose (table sugar), achieve this effect especially well.
Emulsifiers. You’ll notice that the list of ice cream ingredients includes both fats and liquids. Emulsifiers are needed to keep these naturally repellant substances together. Milk proteins do some of this work. Homemade recipes use eggs (cooked for food safety). The food industry uses glycerides, members of the lipid family. Unlike their “relatives,” the fats, glycerides have a component that bonds with water.
Stabilizers. When you carry ice cream a distance from the store to your freezer, it begins to melt and then later refreezes. Stabilizers keep water locked in the ice cream. Otherwise, when melting occurs, the water would separate from the other ingredients, forming larger crystals each time it happens. Eventually the crystals would coarsen the ice cream’s texture.
Many stabilizers are gums, jellylike starches with great water-holding capacity. As their name suggests, they also add a slightly chewy quality to the texture.
Churn Up the Volume Ideally, ice cream is an even blend of tiny particles of nonliquids, like fats and milk solids, in liquids. The ingredients named above all contribute to that end. Processing is just as important.
After the ingredients are mixed, the ice cream is aged in a refrigerator, but only briefly—about four to 12 hours. Aging allows the solids to absorb water for added body. During this time, the fatty end of emulsifiers partly replaces the protein film on fat globules, so the fats can be broken down even more and more finely dispersed.
The ice cream mixture is churned as it freezes. Like beating cake batter, churning distributes ingredients. To keep ingredients small, churning breaks up ice crystals as they form. Equally important, churning adds air, which is as essential to ice cream as it is to cakes and soufflés. You might even say that it’s air, as much as cream, that puts the “cream” in ice cream. Just the right amount is needed to achieve a soft, “scoopable” consistency. Economy brands may be close to 50 percent air by volume. Premium brands are about 15 percent air, making them dense and mousse-like. With less air, there’s more ice cream, so you really do get more for your money than a famous name and a fancy package.
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