Ed in San Francsico asks:

Why is whipping the egg whites is so crucial in making a soufflé?

Chef Stephen answers:

I'm going to refer that question to one of my all-time favorite reference books. Harold McGee's On Food and Cooking contains most, if not all, answers to this kind of food science question. I do know that a really clean bowl and egg whites uncontaminated with yolk is key. This makes for fluffy, tender, full-bodied whipped whites. Let’s see what Harold says:

"No matter what the ultimate use of the foam, whether as a meringue or in a soufflé, whenever the greatest possible lightness or volume is desired, the whites are always beaten alone. Cookbooks insist that not a speck of yolk or any other fatty material be allowed in the bowl, and for good reason. A single drop of yolk in the white of an egg can reduce the foam's maximum volume by as much as two thirds. The effect of other fats and oils is less drastic, but great enough that bowls made out of plastic should be avoided. Plastics are polymers of hydrocarbon chains, which also form the bulk of all fat molecules, and so plastics tend to retain traces of fatty material on their surfaces.

"Fats reduce the volume of albumen foams by getting in the way of coagulation. One of the ways in which protein molecules bond to each other is through the attraction between nonpolar hydrocarbon regions exposed by foaming. Once the foam is formed, however, it can be folded gently into the yolks or other fatty mixtures and do a fine job of leavening. It doesn't matter if the foam slowly degenerates in the mixture, because the important task -- filling the mixture with more air bubbles than it could accommodate alone -- has already been accomplished. This is exactly how souffles and sponge cakes are made."

Hope that helps, Ed. You can buy a copy of McGee’s book at any good independent book store. Or go to

http://www.curiouscook.com/onfoodandcooking.shtml