Egg foams are one of the natural marvels of food chemistry. Fascinatingly, egg whites have been used to make foams since before the Renaissance (read: before the whisk was even invented)! Our ancestors used a variety of surprising techniques to foam egg whites, including wringing egg whites through sponges, slapping the surface with very stiff dried fruit slices, and using bundles of straw as a sort of predecessor to the modern whisk. Egg foams can be incorporated into a variety of dishes, such as meringues, cakes, soufflés, sauces, mousses, and cocktails. But wait, this is confusing. You may find yourself asking: Why would I want to use eggs that are a few weeks old?
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Does it matter what kind of bowl I use? Do I really need to use cream of tartar, or is salt an okay substitute? How will I know if I’ve overbeaten them, and what the heck is a stiff peak anyway? ? …whew!
So many rules for something so simple! ! I ll break it down for you, so you can decide which “rules” you want to follow and which you want to throw out the window. But first a little science, so we can understand why there are rules at all. All foams are a type known as a, in which air is dispersed throughout a (usually) liquid phase without dissolving.
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The special proteins in egg whites are what allow stable foams to form. Proteins are large molecules, as molecules go. Because they’re so big, there are areas along their chain that are (water-loving) and areas that are (water-fearing). In nature, proteins fold themselves into a specific shape based on these characteristics. They keep their hydrophobic areas on the inside, where they are protected from exposure to water, and their hydrophilic areas on the outside.
As I mentioned in my post, when proteins are denatured, they unfold into long, shapeless chains and try to bond with the other proteins around them. Once unfolded, the proteins’ hydrophobic and hydrophilic sides are exposed to the water-rich fluid around them. As you might imagine, this is no problem for the hydrophilic side of the chain, but the hydrophobic side will search for any escape…for instance, in an air bubble! So as your whisk denatures these proteins and simultaneously introduces air bubbles, the unfolded proteins congregate on the surface of each bubble, with their hydrophilic side remaining happily in the egg white liquid, while the hydrophobic side protrudes into the bubble to escape all that terrible water. Meanwhile, the proteins are forming bonds with each other around the surface of the bubble, thereby creating a strong and stable network of protein that keeps the air trapped and dispersed throughout the fluid egg.
COOL! Here are the top ten rules for making egg foam. Some I debunk, some I validate. Why. Warmer temperatures lower the surface tension of liquid egg whites, thereby making it easier for bubbles to form.
Cold eggs are also easier to separate and run a lower risk of the yolk breaking and leaching destructive fat into your egg whites (see number 8 below). Is it for real?