The Sophisticated Kitchen: Perfecting the Roux

A roux is still a roux, no matter what you call it—but perhaps 'fat and flour paste thickener' might be a more approachable name. The fancy French term can be a bit off-putting, but don’t let that stop you from mastering this classic kitchen technique.

This is part of The Sophisticated Kitchen, Skillet’s series created to address your basic cooking questions and fill in any gaps in your home chef knowledge.

The significance of a roux in gravies, sauces, and soups cannot be overstated, yet there are many home cooks who haven’t even tried it. The good news? A roux is simple to master, and we’re here to guide you through every step, slowly and carefully.

But why do we need these French techniques? Why not just throw some starch into a pot and let it thicken everything by itself? Harold McGee, in his essential food science book On Food and Cooking, explains that adding flour or starch directly to hot liquid causes clumping, which never disperses evenly. When starch hits hot liquid, the granules form a sticky, partially gelled surface that traps the dry particles inside, preventing them from spreading. Cooking the starch in an equal amount of fat beforehand helps separate the granules, allowing them to merge smoothly with their new liquid partner, rather than seizing up when they meet.

A roux—whose name actually means 'red'—is simply a blend of fat and flour that’s been lightly cooked (or cooked for longer, depending on the desired result). There are three key stages to look out for when making a roux:

• White: At this stage, the moisture has evaporated, and the roux appears slightly bubbly or frothy, with no noticeable color change. This process takes about three minutes, depending on the fat used, and eliminates any raw flour taste. White roux has the strongest thickening properties.

• Blond: At this point, the flour takes on a pale tan or yellow hue and develops a more pronounced flavor compared to white roux.

• Brown: As the name suggests, this roux turns brown, gaining a nutty, toasted flavor. Brown roux is most commonly used in Cajun and Creole cooking and has the least thickening power. To avoid burning the butter, it’s best to use oil with a high smoke point instead of butter.

Get the Measurements Right

A roux requires equal amounts of fat and flour, but not all methods of measuring are equal. While some recipes call for equal spoonfuls of each ingredient, using mass is the secret to making the perfect roux.

This doesn’t mean that a roux measured by volume won’t thicken, it just won’t be as effective. To illustrate the difference, I made two gravies. The first one was made the usual way: I measured out about two tablespoons of butter, weighed it, and then measured the equivalent weight of flour (32 grams each, which was roughly three tablespoons of flour). After melting the butter, I added the flour and stirred it continuously with a wooden spatula until it reached that frothy, still-pale stage.

I poured in a cup of duck stock and watched, somewhat horrified, as everything started to clump together.

Fortunately, with a little vigorous stirring, the flour granules broke up and got to work, transforming the simple broth into a rich, hearty gravy.

I then poured the finished gravy over some crispy home fries, added peas, cheese, and a few other random ingredients. It turned out to be quite delicious.

To compare, I made another batch of gravy, this time measuring everything by volume. As expected, the roux was a little thinner and, as you can see from the photo below, it didn’t have the thickening power needed to handle a whole cup of stock.

The takeaway here, my friends, is to measure by weight if you want to create gravy that truly packs a punch.

Paint It Right

A darker roux adds a rich flavor to anything it’s mixed with, but remember that it’s the flour you want to brown, not the cooking oil. If you’re aiming for a deep, chocolate-colored roux, butter might not be the best choice, as the milk solids can burn and impart a harsh flavor rather than a rich, nutty one. To demonstrate how much of a difference the oil makes, I made two different brown gravies using darker roux: one with regular butter and one with clarified ghee. The butter-based roux took about 12 minutes to reach a dark, almost milk-chocolate brown shade:

The ghee-based roux, on the other hand, took almost twice as long to reach the same depth of color (and was also looser, though this didn’t affect its thickening ability):

I then turned both roux into gravies, and while they both thickened beautifully, the butter-based gravy had a burnt, acrid taste, while the ghee gravy had a smooth, nutty flavor with a rich depth.

A Word on Liquids and Their Temperatures

Many people believe that your liquid—whether it's stock or milk—needs to be warmed before adding it to a roux. On the other hand, some argue that it doesn't matter, especially with white, dairy-based sauces like béchamel.

Personally, I've added milk and stock to roux at various temperatures, and honestly, I've never noticed a difference. (I tend to use cold liquids because I don't want to bother with heating them up beforehand.) For me, the secret to smooth, lump-free sauces and gravies lies not in the temperature of the liquid, but in how thoroughly you whisk it.

To prepare a basic cheese sauce, I start by making a white roux (about 33 grams of fat and flour each) as described earlier, then I dump—yes, dump—a cup of whole milk into the pan, whisking continuously. Initially, there may be some clumps, but they dissolve and the sauce thickens into a smooth, shiny texture.

Next, I throw in a couple handfuls of cheese, add a squirt of mustard, and season with salt and pepper to create a cheesy sauce that’s perfect for mixing into macaroni or dipping nearly anything.

To summarize: To make a roux, you need to:

1. Measure out equal parts of fat and flour by weight, aiming for approximately 33 grams of each per cup of liquid you plan to thicken.

2. Cook over medium heat while stirring constantly until the desired color is reached. A white or blond roux works well for most gravies and sauces, but a brown roux is preferred for Cajun dishes. If you plan to use a brown roux, opt for clarified butter or other oils with a high smoke point. Duck fat and bacon grease are both flavorful choices.