The kitchen is our science lab: We test recipes over and over again to make sure everything works perfectly. And there's plenty of real science going on in our kitchen and yours -- every time you cook. When your meat browns, your cake rises (or doesn't), or your seafood turns opaque, there is a tiny, invisible reaction going on in your food. So how does a mixture of yolks and clarified butter become a smooth, creamy hollandaise sauce? Let's get semi-scientific and find out.
Anyone who's tried to make salad dressing knows that oil and water don't mix. They've just never liked each other. To get them to stay together permanently, you need an emulsifier. Emulsifiers work because their molecules have one water-loving side and one fat-friendly side, so they act like a mediator between the two substances. You've probably heard of one already: soap. It attracts grease and dirt but still washes off easily in water.
One of our favorite culinary emulsifiers is an egg yolk. When we make hollandaise sauce, the yolks are mixed with lemon juice (which disperses tiny droplets of the emulsifier) before whisking in a steady stream of melted butter. The butter is slowly broken into small droplets which are held in place by the egg yolk. Everything gets thick and creamy because the heat of the butter is cooking the eggs. Too much heat will cause a scrambled mess and not enough will stop the emulsion from forming.
Even though there's a lot of science going on in a little bowl of sauce, it doesn't mean hollandaise is hard to make, start by making our easy recipe. With a little practice, this delicious sauce will become a staple at brunch in your house. Spoon some on poached eggs or steamed asparagus, make a classic eggs Benedict or get adventurous with a hollandaise derivative like bearnaise sauce. If you want to get more into the science of cooking, check out Harold McGee's book "On Food and Cooking: The Science and Lore of the Kitchen."