by Rishidev Chaudhuri
Harold McGee's book, “On Food and Cooking”, changed the ways I cook and think about food (as it seems to have done for many people). Cooking can often seem obscure and unsystematic: recipes and tattered bits of kitchen wisdom abound, but general principles seem harder to come by. And learning to cook is a process of moving from recipes treated as self-contained procedures and rituals to be reenacted to seeing a collection of principles and techniques that can be deployed in various ways. “On Food and Cooking” is a book on the science of cooking: what happens when you brown meat, what happens when you cook asparagus, how dough rises, why coriander tastes the way it does. And its primary value, at least to me, was in dramatically moving me along the road to understanding some of the principles lying behind what we do with food. It's immediately liberating and almost exhilarating to look back on a number of recipes and times in the kitchen and realize what I was actually doing when I was following a particular set of instructions. Most of this food science information existed before but it was scattered through journals and history books. “On Food and Cooking” collects and curates it, and aims it at a broader audience than just the scientist or the historian or the professional cook.
The best example for how this book changed my thinking is its sections on the role of the egg. It is almost universally acknowledged that eggs, even accompanied by little else, are sublime and need not justify their ubiquity. But eggs also play supporting roles in a bewildering parade of dishes (especially in the cuisines of Europe), and in these they take on a variety of structural roles: changing the shape and form of food in addition to changing how it tastes. Making sense of this diversity of uses was enlightening: it allowed me to replace a number of disparate pieces of knowledge with some general principles and these principles then allowed me to think more creatively, beyond the confines of particular recipe patterns. And looking at the roles of eggs in food is also a wonderful lesson in chemistry and the strange hybrid states of matter that live everywhere in food.
For example, consider the various ways of combining dairy (milk or cream) and eggs. There are many, but most reflect a simple basic principle. Eggs thicken — heating an egg makes the proteins unfold and tangle into a mesh that traps liquid. Adding more eggs makes for thicker mixtures. And so the dairy-egg mixture continuum stretches from scrambled eggs with a splash of milk or cream in them (to make them softer and more unctuous) to dairy thickened with a bit of egg, as in eggnog. Adding more dairy to scrambled eggs bring you into custard territory, starting with thick eggy custards, leading through quiches and into softer custards (as in pot de crème and crème caramel) and finally into thickened liquids, like crème anglaise. Of course there is little about this that is specific to dairy and you can use eggs in this way with other liquids, provided they have a bit of salt or mineral in them. You might, for example, try making a quiche but substituting a flavorful stock for the milk / cream, as the Japanese do with dishes like chawanmushi and tamago dofu. Similarly, you might decide to thicken a soup by mixing in some eggs, much as you thicken milk for crème anglaise. This is a common technique and is what the Greeks do with the egg-lemon soup avgolemono.
As I mentioned, the egg proteins are folded up, and heating eggs causes the proteins to unfold and mesh with each other. In a quiche or custard, the resulting structure, though mostly liquid, is no longer mobile. This hybrid state of matter is called a gel: a liquid is dispersed through a solid network. If the eggs are cooked too much or too aggressively, the solid mesh becomes even tighter and eventually squeezes out the liquid, separating into chewy lumps of egg and liquid. This is why eggs and dishes involving them are best cooked gently.
Beaten egg whites form a foam, which is another hybrid structure mixing different types of matter. Egg white foams give exuberant lightness to dishes like mousses, soufflés, meringues and angel food cakes. As in the previous example, the proteins in the egg are cajoled into unfolding and forming a network. Here the network is of bubbles, and the foam is a liquid network trapping bubbles of air. The foams found in newer cooking (introduced by places like El Bulli), use similar principles: work a gas (e.g. air, nitrous oxide, carbon dioxide) into a flavorful liquid and stabilize the network of bubbles so that the foam lasts (using substances like gelatin and lecithin).
Egg yolks have their own special structural roles to play too. Oil and water famously don't mix, but there exist a number of substances that can bridge this age-old opposition to form hybrid oil-water systems, called emulsions. Cooks have used the lipoproteins in egg yolks (of HDL and LDL fame) to emulsify for at least several hundred years, and mayonnaise and hollandaise are the two most prominent examples. Mayonnaise is basically lemon juice yoked to oil with the help of egg yolks (yolk-yoked, as it were), and hollandaise substitutes butter for the oil. Again, the principle can be detached from the particular context and you could substitute other water-soluble liquids for the lemon juice and other fats for the usual oil or butter. You could, if you wanted, use animal fats in your mayonnaise, for example; swapping out some or all of the oil for duck fat makes for a wonderful warm salad dressing. And, if possessed by some deranged experimental extravagance, I imagine you could make a beer and bacon fat emulsion to top a hamburger.
There are several other structural uses for eggs, but these three are the most common. If you'd like to play around with these ideas, here are outlines of common instantiations of a gel, a foam and an emulsion.
The gel is effectively either shirred eggs or a crustless quiche, depending on how much cream you add. I've left the proportions out since it's just a technique and you should play around with various ratios, but you can wander between a tablespoon or so of cream per egg to nearly half a cup. If you don't have ramekins you can make this in a larger dish. Remember that the eggs will continue to set after they've been taken out of the oven, so pull them out when they're still a bit wobbly. Drop a couple of eggs, some cream and some grated cheese into a buttered ramekin and bake in a 325-350 F/160-180 C oven until they are just set. If you're curious how they're doing, poke at them with a fork. It won't harm their deliciousness (and, despite their simplicity, eggs made this way are quite delicious). You can add flavorings before you pop them in (salt, pepper, cayenne or other spices, chives, tarragon and so on).
Meringues are a very clean example of an egg foam. Beat egg whites until they form soft peaks, then add in sugar a tablespoon at a time while beating, until the eggs form stiff dry peaks. Use about 3 and a half to 4 tablespoons of sugar per egg white. Use a spoon to put dollops of the egg foam onto a baking sheet covered with parchment paper. Bake in a very low oven until they are dry and crisp (this can take a while, and will probably be over an hour at 300 F but, again, just poke at them or try one if you're unsure).
Mayonnaise is the classic emulsion and is straightforward to make as long as there's enough liquid before you start adding the oil. Mix an egg yolk with some lemon juice, salt and mustard and gradually whisk in about ¾ cup of oil, adding it slowly at first and then in a continuous stream until it thickens quite substantially. You can add other flavorings, of course; garlic is justifiably popular.
Extra egg whites can be shaken into cocktails (they add a lovely froth to sours), beaten and folded into frittatas and omelettes to give lightness or substituted for regular eggs if you're feeling abstinent. Extra egg yolks can be used for sauces, to add more richness to a custard or scrambled eggs or used to pleasure your lover (http://www.youtube.com/watch?v=NqA-mP0MhZg).