(Or, how to make stuff thick)

I have been inquisitive my entire life. This is not a braggart’s proclamation; on the contrary, I wish I could simply take things as they’re handed to me. But no, I always have to question; I like to know the reasoning behind something, but more importantly I like to know how things work.

When I was a young culinary student, one of the instructors in the preliminary classes stated that we were not there to learn recipes, that anyone can follow a recipe. We were to learn to cook. If you simply learn recipes, he said, that’s what you know. But if you learn to cook, you can you make any recipe, and you probably won’t need them. During those early years my bedtime reading was Harold McGee’s On Food and Cooking, Prosper Montagné’s The New Larousse Gastronomique, and August Escoffier’s Le Guide Culinaire. I was a sponge.

It fascinated me to learn, for example, that starting a stock in cold water had far better results than hot water (albumin, the naturally occurring protein in animals, dissolves in cold water; it coagulates with heat), and that cooking flour before adding it to a liquid yields much more desirable results (fewer lumps, less floury, and more refined flavor). And with the addition of a thickener, mainly flour, a simple yet flavorful broth is transformed into a soup or velvety smooth sauce. The French word for a thickened broth is in fact vélouté, which translates to English as velvety. When liquid takes on a certain viscosity it coats and stays on the palate longer, thus adding texture in the literal sense and also in its flavor.

There are, of course, many ways to thicken a broth. It can be reduced through evaporation, which is done by simmering and skimming until it takes on a syrupy consistency; the flavors, though, become highly concentrated. This has its applications in the professional kitchen, but rarely is this method used at home.

Other options include adding cornstarch, flour, potatoes, rice, butter, and even the lesser used and more archaic method of adding tempered eggs. Of these the most common is flour, but unlike its counterpart, cornstarch, it should never be simply dissolved into broth, boiling or not, at least not with hopes of a promising outcome. Raw flour will most definitely thicken liquid, but flavor and consistency will be compromised. Most likely the result will be lumpy and pasty, not only in physical appearance but also in flavor. Cooked flour, on the other hand, is rendered free of these undesirable traits.

So how do professional cooks create such satiny smooth and lump-free soups and sauces? Invariably the answer is roux (pronounced roo), or equal parts fat and flour cooked to varying degrees of doneness. Sure, there will be some young culinary Turks who conclude that roux is passé. Its time-honored tradition has been banished by many, just as it was when a group of talented young French chefs in the 1960s rocked the unsinkable boat of cuisine classique and began serving flourless reduction sauces in what became known as cuisine nouvelle, or new cooking. Unfortunately (or fortunately, depending on your views), as brilliant as the chefs were, nouvelle cuisine ultimately became somewhat of a parody of its original intention, just as “tall food” did a decade ago.

I first encountered the anti-roux movement while applying for a sous chef position in New Orleans about 20 years ago. The chef, nice as he was, was interrogating me with a barrage of questions. Why did I choose cooking as a profession? What was my favorite style of cooking? How do you make this or that? But it was the gleam in his eye that gave it away when he tucked in his chin and almost whispered, almost demanded, in his Franco-Germanic accent, “And you do not thicken demi-glace with roux, no?” I lied, or at least stretched the truth a bit, and said, “But of course not, chef; triple reduction and monter au beurre [mounted with butter].” I was hired on the spot, but as fate would have it, I never did work at his restaurant.

Flour-thickened soups and sauces, when done correctly, have their place. In fact, when roux is used correctly it is used in conjunction with the reduction method, which occurs naturally as a soup, sauce, or stew simmers. As mentioned, roux is nothing more than a mixture of fat and flour that has been cooked together. Cooking them together removes the raw flavord, and the amount of fat you’re adding to the recipe is nominal; much of it can be skimmed off as it simmers. If you’ve ever made traditional pan gravy by adding flour to drippings, then you’ve made roux.

The beauty of cooking flour in fat is that it not only thickens liquid, it also adds color and flavor. The word roux is said to be derived from an antiquated variation of the French word rouge, meaning red, which no doubt refers to the change of color that occurs as flour cooks. The longer it’s cooked the darker it becomes. In fact, types of roux are denoted by their color. The three most common gradations are white, blond, and brown.

Generally speaking, dark roux is added to dark liquids, such as sauces and stews, and white and blond roux are added to white or lighter-colored liquids, such as vélouté and cream soups. Besides color, another thing to consider is how much roux will be required. As flour cooks some of its thickening ability is diminished; the longer it cooks and darker it becomes the less it will thicken, because gluten, the flour’s protein, begins to break down at high temperatures. It takes a greater amount of brown roux to thicken the same amount of liquid as a white roux.

There is another even darker roux called roux noir (black roux), used almost exclusively in Cajun cooking. It’s not actually black—that would taste burnt—but it is very brown. This dark color is achieved by heating oil (as opposed to butter, because oil has a much higher smoke-point) to almost smoking then stirring in flour and cooking it until the flour browns. Roux is such a ubiquitous component to Cajun cuisine that more often than not a traditional recipe will begin “first make a roux.”

When making roux, particularly the Cajun variety, safety precautions should be observed. Fat of any kind can become extremely hot, more than twice as hot as boiling water, and coupled with flour it becomes a sort of molten culinary lava; it sticks to the skin and burns on contact. For this reason you should take great care in its preparation. But roux can be made ahead of time and if you find yourself with an excess of the thickener it can be refrigerated in a sealed container for future use.