A Common Myth About Beating Egg Whites Was Finally Busted
Separating eggs is a skill that experienced bakers and cooks take a lot of practice in order to get right. In addition to making sure no pieces of the shells end up in the liquid, many recipes call for either the whites or the yolks only. While there is a secret to separating eggs you'll wish you knew sooner, you literally can't become an expert at separating whites from yolks without breaking a few eggs along the way.
Baked goods often require egg whites, like noted on this list of 47 dessert recipes you'll need egg whites to complete that Epicurious compiled. Examples include meringue for cookies and pies, and those pretty little macaroons. Conventional wisdom has stated that in order to perfect these recipes your whites need to be completely free of any yolk whatsoever. Serious Eats, for instance, warned not to use whites that contain any trace of yolk when you need beaten egg whites to complete a recipe.
As is often the case, the scientific process has revealed a flaw in that conventional wisdom.
Imperfect egg whites aren't worthless
It turns out that the hard and fast rule that you need immaculate egg whites to produce proper peaks for baked goods isn't so hard and fast. Serious Eats addresses its own proliferation of that idea.
The outlet explains the science behind that belief in making things like a meringue recipe. As Science Sparks points out, the fat in egg yolks counteracts the reaction you need to happen, which is the mixture of egg whites and sugar fluffing and stiffening. What Serious Eats sought to examine is whether the presence of even minuscule amounts of those fats could wreck the entire process.
Through a few test runs, they found that a visible drop of yolk in the whites did not short-circuit the formation of stiff peaks. It did, however, delay the process and require more beating to get to that point. Also, the test revealed more than a single drop of the yolks did prevent the mixture from puffing up. The prevailing advice still seems to be that it's best to avoid yolk as much as possible, as Food Crumbles also suggests.
If you can see a speck of yolk in your egg whites, not need to throw out the whole batch and start over, though. You just might be in for a little more work, especially if you're beating the mixture by hand. Still, avoid this mistake when whipping your egg whites and try to keep them as clean as you can.