I teach organic chemistry to sophomores who would rather be anywhere else, and I have found exactly one way to make them sit up: talk about dinner. Every reaction on this page happens in an ordinary kitchen, and once you know what's going on, you cook better. No equipment needed beyond a stove and a little curiosity. Let's go.

Flour has two proteins, glutenin and gliadin, that don't do much until you add water and knead. Then they link up into a stretchy network called gluten. Meanwhile the yeast, which is a living fungus, eats the sugars in the dough and gives off carbon dioxide gas and a little alcohol. The gas gets trapped in the gluten network like air in a balloon, and the dough rises. In the oven the gas expands, the alcohol boils off (that's part of the smell), and around 140°F the yeast dies and the gluten sets. Knead too little and the network can't hold the gas; knead too much (hard to do by hand) and it tears.

Try it: mix a spoonful of yeast, a spoonful of sugar and half a cup of warm water (about 100°F, not hot) in a glass. Ten minutes later you'll have foam. That's the gas.

When proteins and sugars are heated together above about 300°F, they react in a cascade that produces hundreds of new flavor and aroma compounds and brown color. This is the Maillard reaction, named for the French chemist who described it in 1912, and it is responsible for the crust on bread, the sear on a steak, the color of roasted coffee and the flavor of a toasted marshmallow. It needs heat and a dry surface, which is why a wet steak steams gray and a patted-dry steak browns. Caramelization is a different reaction: sugar alone, cooked past about 320°F, breaking down into its own set of nutty, bitter compounds. Onions do both at once, which is why they take forty minutes to get really sweet and there's no shortcut.

An egg white is mostly water with proteins floating in it, each one folded up into a little ball. Heat makes the balls unfold (denature), and the unfolded strands tangle and bond to each other (coagulate) into a solid mesh with the water trapped inside. Whites start setting around 145°F and yolks around 150°F, which is why a gently cooked egg is tender and a boiled-hard one is rubbery: too much heat squeezes the mesh tight and the water leaks out. It is also why you add a little milk to scrambled eggs (it dilutes the proteins so the mesh stays loose) and why you cook custard slowly. Whipping does the same unfolding with air instead of heat; that's a meringue.

Oil and water don't mix, and yet mayonnaise is mostly oil held in a little lemon juice and egg yolk. The yolk contains lecithin, a molecule with a water-loving end and an oil-loving end. It coats each tiny droplet of oil and keeps the droplets from finding each other. That's an emulsion. The rule is to add the oil slowly at first, so the droplets stay small; dump it in and it "breaks" into a greasy mess. Vinaigrette is a temporary emulsion (mustard helps), hollandaise a butter one, and milk is a natural one, which is why it looks white: light scattering off billions of fat droplets.

Baking soda is sodium bicarbonate, a base. Mix it with an acid (buttermilk, yogurt, lemon juice, brown sugar) and water and it fizzes carbon dioxide at once, so get the batter in the oven quickly. Baking powder is baking soda with a dry acid already mixed in, plus starch to keep it dry; "double-acting" powder has one acid that works when wet and another that works when hot, so it gives you time. Use soda when the recipe has its own acid, powder when it doesn't, and never swap them one for one: soda is about three times as strong, and too much tastes soapy.

Salt doesn't just taste salty. It suppresses bitterness (a pinch in coffee or grapefruit, try it), draws water out of vegetables by osmosis (salted eggplant, salted cucumbers), and in meat it does something better: dissolve some salt into the water in the muscle and the proteins hold onto moisture instead of squeezing it out when cooked. That is what a brine does to a turkey, and why a salted-ahead pork chop is juicier. In bread it tightens the gluten and slows the yeast so the loaf rises evenly instead of blowing up.

Nothing here is dangerous, but the usual kitchen rules apply: hot pans are hot, and a sugar syrup past 300°F will give you a nasty burn. If you want more, the library has several fine books on the science of cooking, and any general chemistry textbook will explain denaturation and emulsions in more detail than you ever wanted.

Neighbors worth a visit: Science at Home (experiments for the kids), Sourdough Sam (a man who understands yeast), The Cheese Course (proteins and fat, aged), Where Thinking Machines Are Going (my colleague down the hall, who thinks bigger than I do), and the ResearchTriangle neighborhood.