How often have you beaten egg whites for a recipe? Soufflés, meringues, angel food cakes, and chiffon pies all depend on airy whites for their loft. And what about whipping cream? Not only is it the secret to ethereally light mousse (such as Raspberry & Blackberry Mousse) but whipped cream is also perfect for layering into strawberry shortcake, topping pie, or garnishing a simple ice-cream sundae.
As you whip egg whites or cream and the liquid billows into an airy mass, a similar transformation seems to occur in each. But plumes of whipped egg white and cream have less in common than you might think. They are alike in one important way, however: They’re both foams. Like soapsuds and the head on beer, beaten egg whites and whipped cream trap air in a soft network of stable bubbles.
Protein and fat stabilize bubbles
When you blow air through a straw into a glass of water, bubbles form and quickly disappear. But when you whisk air into egg whites or cream, bubbles form—and linger—because the proteins present in these viscous liquids stretch around bubbles and trap them.
Here’s where the foams differ: In whipped egg whites, proteins alone do all the bubble building. In whipped cream, proteins share the task with another substance—fat. This important distinction influences how cooks use beaten egg whites and whipped cream in recipes, so let’s take a closer look at how each forms.
Egg whites trap bubbles in a web of water and protein. Egg white is a mixture of protein (10%) and water. The action of beating creates bubbles and, at the same time, coaxes the coiled egg white proteins to uncurl and regroup into flexible mesh-like sheets that wrap around the bubbles. With continued whipping, the bubbles get smaller, and the froth thickens into a stable mass.
Fat: friend or foe? Whipped egg whites can billow up to eight times their original volume. But a drop of yolk or a little grease lingering in a mixing bowl can reduce the egg whites’ foaming power by two-thirds. That’s because the fat bonds with the egg proteins before they can bond with one another and form those mesh-like protein sheets necessary for trapping bubbles.
While the tiniest speck of fat is the downfall of whipped egg whites, in whipped cream, solid butterfat works with milk protein to build foam. Whipping chilled cream not only re orders milk proteins into films for bubble building, but it also causes the microscopic clusters of solid butterfat that are suspended in the cold liquid to surround and stabilize each bubble. If the butter fat gets warm and melts, however, the foam will collapse.
Foams are fussy
Egg whites whip to their greatest volume at about 70°F. When whites are warm, they don’t cling together as much, making it easier to incorporate air. Cream, on the other hand, whips best when the cream, the bowl, and the whisk are very cold (45°F or lower) and the butterfat is solid.
When it comes to choosing eggs for whipping, professional opinions differ. As eggs age, the whites become thinner and whip easily to great volume. Fresher eggs are more viscous so they take longer to beat, but some cooks think that the resulting foam is more stable. For making clouds of meringue in particular, we opt for older whites and extra volume and add a little cream of tartar to stabilize the foam. With cream, it isn’t age that affects fluffiness and stability, but fat content and temperature. Cream with more fat makes stiffer and more stable foam. Heavy cream, which is 36% to 40% fat, whips into stiff, stable foam; whipping cream, at 30% to 36% fat, makes a softer, less stable foam.