Egg yolks are one of my favorite examples of things that look simple but really, really, really are not. Its structure is intricate, much like a Chinese se

Egg yolks are one of my favorite examples of things that look simple but really, really, really are not. Its structure is intricate, much like a Chinese set of nested spheres carved from a single block of jade. We see the first layer of structure whenever we cut into a hard-cooked egg. Where heat gels the white into a smooth, continuous mass, the yolk sets into a crumbly mass of separate particles. The intact yolk turns out to consist of spherical compartments about a tenth of a millimeter across, each contained within a flexible membrane, and so tightly packed that they’re distorted into flat-sided shapes (much like the oil droplets that egg yolk stabilizes in mayonnaise; see p. 626). When a yolk is cooked intact, these spheres harden into individual particles and give the yolk its characteristic crumbly texture. But break the yolk out before you cook it so that the spheres can move freely, and it becomes less granular. What’s inside these large yolk spheres? Though we think of the yolk as rich and fatty, in fact its chambers are filled mostly with water. Floating in that water are sub-spheres about one hundredth the size of the spheres. The subspheres are too small to see with the naked eye or to be broken up by a kitchen beating. But they can be seen indirectly, and disrupted chemically. Yolk is cloudy because these subspheres are large enough to deflect light and prevent it from passing through the yolk directly. Add a pinch of salt to a yolk (as you do when making mayonnaise) and you’ll see the yolk become simultaneously clearer and thicker. Salt breaks apart the light-deflecting sub-spheres into components that are too small to deflect light—and so the yolk clears up. And what do the subspheres contain? A mixture similar to the liquid that surrounds them in the spheres. First, water. Dissolved in the water, proteins: hen blood proteins outside the subspheres; inside, phosphorus-rich proteins that bind up most of the egg’s iron supply. And suspended in the water, subsubspheres about 40 times smaller than the subspheres, some of which turn out to be familiar from the human body. The subsubspheres are aggregates of four different kinds of molecules: a core of fat surrounded by a protective shell of protein, cholesterol, and phospholipid, a hybrid fat-water mediator which in the egg is mainly lecithin. Most of these subsub-spheres are "low-density lipoproteins," or LDLs—essentially the same particles that we keep track of in our own blood to monitor our cholesterol levels. Stand back from all these spheres within spheres and the picture becomes less dizzying. The yolk is a bag of water that contains free-floating proteins and protein-fatcholesterol-lecithin aggregates—and these lipoprotein aggregates are what give the yolk its remarkable capacities for emulsifying and enriching. McGee, Harold. On Food and Cooking (Kindle Location 2093). Simon & Schuster, Inc.. Kindle Edition.