How To Thicken Sauces With Cornstarch Or Flour (And More!): Tips and Techniques for The Best Results

There’s nothing quite as disappointing as a watery sauce. You know the type—slipping off your spoon like it’s in a rush to exit the plate, leaving your chicken, pasta, or veggies stranded without their silky companion. A sauce without the proper viscosity doesn’t just lack body; it can compromise the flavor delivery and mouthfeel of the entire dish. Fortunately, two kitchen MVPs—cornstarch and flour—can come to the rescue. Whether you’re crafting a glossy stir-fry glaze or a hearty gravy for mashed potatoes, understanding how to thicken sauces with cornstarch and flour is a foundational skill in any cook’s toolkit.

How to Thicken Sauces Using Flour

Flour has been thickening sauces since long before instant ramen was a thing. It’s a pantry staple for a reason: cheap, reliable, and relatively neutral in flavor when cooked properly. To thicken with flour, you’ll want to first create a slurry—not a fancy dance move, but a simple mix of flour and cold water. Use roughly two tablespoons of all-purpose flour mixed with a quarter cup of cold water per cup of sauce. Cold water is key; it helps disperse the flour evenly, so you’re not stuck playing “whack-a-lump” with your whisk.

Once stirred in, simmer the mixture over medium heat. Patience here pays off—flour takes a little time to reach its full thickening potential. You’ll know it’s ready when the sauce is bubbling and visibly thickened. Let it cook for at least another minute to banish any raw flour taste. And don’t skip the stir. Unattended flour sauces have a tendency to develop lumps or scorch faster than you can say “Why is this burnt?”

How to Thicken Sauces With Cornstarch

If flour is the slow-and-steady traditionalist, cornstarch is its speed-dating cousin. It thickens more quickly and yields a glossy, almost translucent finish that’s perfect for stir-fries, Asian-inspired sauces, and dessert glazes. You’ll need less of it, too—one tablespoon of cornstarch mixed with one tablespoon of cold water per cup of sauce will usually do the trick.

Just like with flour, the key is the slurry. Stir your cornstarch and cold water until it forms a smooth paste, then pour it into the simmering sauce. Things will move quickly from here: within a couple of minutes over medium heat, your sauce will go from thin to glossy and clingy. Keep it on the heat for about two minutes more to eliminate any starchy flavor. Be cautious not to overdo it, though—cornstarch-thickened sauces can break down if cooked for too long or exposed to too much acid.

The Roux Is in the Room

If you’re after more flavor—and a richer, silkier sauce—then it’s time to embrace the roux, that classic French trick. A roux is made by cooking equal parts flour and fat (usually butter) together until smooth, then adding your liquid. This method is the backbone of gravies, cheese sauces, and creamy soups like chowders and bisques. Cooking the flour in fat not only improves flavor but also prevents lumps before they can even think about forming. It's a few minutes of stirring that pays off in major creamy dividends.

How to Thicken Sauces Without Flour or Cornstarch

Cornstarch and flour may be the dynamic duo of sauce thickening, but they’re not the only players on the field. Egg yolks, for instance, are ideal for emulsified sauces like hollandaise or custards—although they require a gentle hand to avoid curdling. Meanwhile, vegetable or bean purees can add both thickness and nutrition. Think of blended carrots in a curry sauce, or mashed white beans in a stew. They may alter the flavor and color slightly, but that’s not always a bad thing—sometimes, it’s what makes a sauce truly memorable.

How to Choose Your Thickener Wisely

Not all thickeners are created equal—and not all are interchangeable. If you’re making a dairy-heavy sauce, a flour-based roux may be your best bet for that creamy mouthfeel. If you're finishing a stir-fry or making a sweet glaze, cornstarch is likely the way to go. Texture, clarity, and even the cooking time can affect your choice. High-acid sauces can weaken cornstarch, while flour needs longer cooking to smooth out. And if you’re reheating your sauce later, flour tends to hold up better than cornstarch, which can lose its thickness after cooling.

How to Store Leftovers and Reheat Them Without Ruining the Texture

Once you've nailed that perfect consistency, the last thing you want is to ruin it in the fridge. Cornstarch-thickened sauces may go watery upon reheating, especially in the microwave. A gentle stovetop reheat, with a touch more slurry if needed, usually brings it back to life. Flour-based sauces are sturdier, but even they can suffer from separation or congealing. Give leftovers a slow warm-up, and whisk vigorously to restore their original glory.