Whip It Up!

Do you like lemon meringue pie? Did you know that the white meringue topping is made from egg whites? Making a meringue is an amazing trick. You start with a small amount of a clear, yellow liquid, and end up with huge mounds of fluffy white foam. This happens partly because of denaturation. The protein knots we talked about before can't withstand the beating, and they fall apart. But the whipping process also mixes a lot of air into the egg whites.

If you've never seen the changes egg whites undergo, it's a cool experiment to try. Take two eggs from the refrigerator, and separate the whites from the yolks while the eggs are cold (ask an adult for help). Make sure that there is absolutely no dark-yellow yolk mixed in with the whites. Then let the egg whites stand on the counter for about 30 minutes to warm up a little. Pour them into a large bowl made of glass, ceramic, copper, or stainless steel that has been carefully cleaned. Using either a hand whisk or a mixer (which is much easier), start beating the egg whites. Take a look at them every few minutes to observe what's happening.

First you'll notice that the egg whites form bubbles, although they're still yellow at this point. Then you'll notice that the liquid turns white, but is still thin and bubbly. Pretty soon, however, you'll notice that the egg whites become stiffer. If you lift the beaters out of the beaten egg whites, they form little peaks that bend over (this is called the soft-peak stage). But keep going! Eventually, you'll get stiff, shiny peaks that look like little snow-covered mountains (not surprisingly, this is known as the stiff-peak stage). At this point, you can even turn the bowl over, and the beaten egg whites won't come out. It's a pretty amazing transformation!

If you like to cook, you can sweeten the beaten egg whites with sugar, and bake them to make a kind of cookie called a meringue. You can even flavor the egg whites with things like chocolate or coconut. Do a Google search for a recipe!

The White Stuff

Now that we've talked about eggshells and the thin membrane that lines them, let's move on to the egg white. The egg white is the clear, light yellow liquid that surrounds the darker yellow yolk (more on that later!). Wait a minute - why is it called the egg white if it's yellow? Anyone who has seen a hard-boiled egg knows the answer to that. The yellow liquid becomes a white solid when it is heated. But what's in the egg white, and why does it change in this way? And can we change the color in any other way?

The egg white is also known as albumen (pronounced al-BYU-min). Egg whites are mostly (85%) water, but some protein molecules are dissolved in it. These proteins are long, stringy molecules which normally have particular shapes when dissolved in water. When they are heated, the proteins denature, or become a big tangled mess. Imagine a bunch of long strings that are all tied into the same kind of very fancy knot - that's sort of like the original proteins. Then picture all of those knots untied, and all the strings become tangled up into a big ball - that's what denaturation does. The change in color from light yellow to white is caused by this change in shape.

We can denature albumen proteins in ways other than heating. For example, if you pour some rubbing (isopropyl) alcohol into egg whites, you'll see white streaks forming. The proteins can't keep their knotted shapes in alcohol, so they become denatured. Another way of denaturing proteins is by beating them. That will be the topic for the next post.