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.
How long to beat?
Recipes for soufflés and sponge cakes often say to whip the egg whites until soft peaks curl as you lift the beater. At this stage, the whites remain flexible, so they blend easily with other ingredients. But more important, the air bubbles are still elastic enough to expand in the oven. This allows the framework of a soufflé to stretch higher before its proteins coagulate and set in the heat of the oven.
For chilled or frozen desserts, like mousses, where there will be no further cooking after the eggwhite foam is added, creating a strong foam—as opposed to one that’s flexible enough to expand further in the oven—is the primary consideration. So beat the whites to the stiff (but not dry) stage. At this stage, the foam contains more tiny bubbles, and there’s strength in numbers.
Use ’em or lose ’em. Have you ever beaten whites to perfect medium-stiff peaks, turned away for a few moments to measure the other ingredients, and returned to fi nd your foam looking dry, clumpy, and overbeaten? That’s because egg-white foam exposed to air quickly begins to coagulate and lose its elasticity. So if you’re beating egg whites to soft peaks without sugar for a cake or soufflé, be sure to have all the remaining ingredients ready to go and add them as soon as the whites are beaten.
Overbeating makes foams flop. Beating makes foams expand, but it can’t go on indefinitely. If egg whites are whipped too long, the billowy foam becomes dry, clumpy, and too brittle to support a soufflé. Overbeaten cream poses another problem, as it separates into curds (butter) and whey (buttermilk).
Now that you know how foams work, the stage is set for the loftiest souffl és and lightest mousses you’ve ever made.
|Temperature||about 70°F (to warm eggs, soak them in warm water for 10 minutes)||the colder the better, 33° to 45°F|
|Volume||increase 6 to 8 times||increases 2 to 3 times|
|How to hold||not recommended||refrigerate, covered, in a cheesecloth-lined strainer, for up to 3 hours|
|Signs of overbeating||appear dry and lumpy; liquid separates out; hard to blend with other ingredients||no gloss, looks grainy and curdled|