Folding is a simple yet artful and essential technique used for incorporating an ingredient that has had air bubbles whipped into it, such as whipped egg whites or whipped cream, into a heavier mixture like a batter, so that it retains its light and airy quality. It can be used to create a cloudlike quality for all manner of desserts.
When combining the two ingredients, you want to keep as much of the aeration from the light ingredient as possible. Whisking or beating the two together would knock the air and fluffiness straight out of the mixture. Folding, however—using the lightest hand possible—allows the mixture to remain well aerated. The best tools to do this with are a large rubber spatula or large metal spoon and a large bowl. The technique is simple and an essential for any cook.
METHOD FOR FOLDING
1. Place the heavier mixture in a large bowl.
2. When folding a light ingredient into a particularly heavy mixture, take about one-quarter of the light ingredient and gently stir it into the heavy mixture to lighten it up a bit.
3. Place the remaining light ingredient on top of the heavier mixture.
4. With a rubber spatula or large metal spoon (the large surface of a spoon is useful as it means you need fewer passes to fold the two mixtures together), cut through the mixtures with the side edge of the spoon or spatula until you reach the bottom of the bowl, then draw the spoon along the bottom of the bowl. Turn your wrist to bring the spoon up the side of the bowl, lightly bringing the mixture from the bottom to the top, and as you do so, turn the bowl about 45 degrees and lightly overturn the spoon to gently fold the mixture on top of the light ingredient. Turning the bowl as you fold will incorporate the mixtures more efficiently. Continue cutting into the mixture and folding until just incorporated. I find that twenty turns are almost always the right number, so I count as I fold.
Always work slowly and gently. Do not be tempted to overmix and unnecessarily knock extra air out of the mixture. If necessary, err on the side of underfolding. When adding a light-colored mixture to a darker mixture (such as whipped egg whites to a chocolate mixture), be sure to fold until no streaks of white remain.
WHIPPING EGG WHITES
Egg whites can be beaten or whipped with a whisk, electric hand beater, or heavy-duty mixer using the whisk attachment. Beating raw egg whites vigorously makes the egg proteins uncurl, and as air bubbles are beaten in, the uncurled proteins link together, enclosing the bubbles and locking them in, resulting in a light and extremely airy opaque foam. Egg whites form undulating waves with soft peaks, when the tips of the peaks curl over on themselves, or stiff peaks, when they hold themselves straight upward, clinging tightly to the whisk when lifted up. The stiff peak stage (or just before) is required if you are folding egg whites into a heavier mixture and then baking in the oven.
Tips for Whipping Egg Whites
• Eggs are easiest to separate when cold, but whites will beat to their fullest volume at room temperature. So plan ahead!
• Use a large bowl, since egg whites can grow 10 to 12 times their volume when beaten.
• If you have a copper bowl, use it; the copper reacts with the egg whites, helping to create a more stable protein structure. But you can whip egg whites very successfully in stainless steel or glass bowls. Avoid plastic bowls, as the surface can hold grease that keeps the whites from whipping properly.
• Make sure your bowl is clean and dry before starting. If you notice any kind of greasy film on the surface of the bowl, use lemon juice or vinegar to clean the bowl before you begin.
• Make sure your egg whites are free from contamination, especially a runaway drop of yolk, as the fats in the yolk can keep the whites from forming stiff peaks. Use a piece of eggshell to remove any unwanted egg yolk or pieces of shell from the egg white.
• Egg whites can be overbeaten and become “dry,” where the whites lose their silky appearance and begin to look clumpy and almost curdled. Stop whisking when the whites are stiff and fluffy.
• Use whipped egg whites right away or they will begin to liquefy.