You can thicken almost any liquid using a starch, a gum, an egg yolk, or simply by simmering it down. The method you choose depends on what you’re making, what texture you want, and whether the liquid will be served hot or cold. Here’s how each approach works, with the specific ratios to get it right.
Cornstarch and Flour: The Everyday Options
Cornstarch and all-purpose flour are the two most common thickeners in home kitchens, and they work differently enough that it’s worth knowing when to reach for each one.
For a medium-thick sauce, use one tablespoon of cornstarch mixed with one tablespoon of cold water per cup of liquid. This mixture is called a slurry. Whisk the slurry into your simmering liquid and stir constantly for about one to two minutes until it thickens. Cornstarch produces a glossy, somewhat translucent finish, which makes it ideal for stir-fry sauces, fruit fillings, and gravies where you want a clean look.
Flour requires roughly twice the amount: two tablespoons of flour whisked into a quarter cup of cold water per cup of liquid. Flour-thickened sauces turn out opaque and slightly matte, which suits cream sauces, stews, and chowders. You can also cook flour in fat first to make a roux, which eliminates the raw flour taste and gives you more control over the final color and flavor. A light roux (cooked for two to three minutes) thickens the most. A dark roux adds deep flavor but less thickening power because the longer cooking breaks down more of the starch.
One important rule for both: always mix them with cold liquid before adding them to your pot. Dumping dry starch into hot liquid creates lumps that are nearly impossible to smooth out.
Arrowroot and Tapioca Starch
Arrowroot powder works at about the same ratio as cornstarch (one tablespoon per cup of liquid) and produces an even clearer, more neutral-tasting result. It’s a good choice for thickening acidic liquids like citrus sauces or tomato-based dishes, where cornstarch can sometimes lose its thickening power. Arrowroot also holds up better in dishes that will be frozen and reheated.
Tapioca starch, sometimes labeled tapioca flour, creates a slightly stretchy, glossy texture. It works well in pie fillings and puddings. Use about one and a half tablespoons per cup of liquid. Like cornstarch, mix it into a cold slurry first.
Xanthan Gum: A Little Goes a Long Way
Xanthan gum is a fermented powder that thickens liquids without heat, which makes it useful for cold sauces, salad dressings, smoothies, and gluten-free baking. You need very little. A concentration of just 0.3 to 0.5 percent by weight creates noticeable thickness, and the viscosity climbs steeply as you add more. For a practical starting point, that’s roughly a quarter teaspoon per cup of liquid.
Sprinkle it in while blending or whisking vigorously. Xanthan gum clumps easily, and once those clumps form, they’re stubborn. A blender or immersion blender works best. One advantage of xanthan gum is stability: its thickness stays consistent across a wide range of temperatures, and salt has minimal effect at lower concentrations. It also doesn’t break down with reheating the way some starches do.
Egg Yolks for Rich, Creamy Thickness
Egg yolks thicken custards, curds, and cream sauces through a combination of emulsification and gentle protein coagulation. The key is temperature control. Yolks begin to thicken a liquid around 65°C (149°F), but they start to solidify and curdle at 70°C (158°F). That leaves you a narrow window of about five degrees to work in.
The technique is called tempering. Whisk a small amount of your hot liquid into the beaten yolks to warm them gradually, then pour the yolk mixture back into the pot while stirring constantly. Keep the heat low and stir until the sauce coats the back of a spoon. Never let it boil. If you overshoot and see bits of scrambled egg forming, strain the sauce immediately through a fine mesh sieve. Two to three yolks will thicken about a cup and a half of liquid into a velvety sauce.
Reducing: No Thickener Needed
Reduction is the simplest method conceptually. You simmer a liquid uncovered until enough water evaporates to concentrate what’s left. This intensifies both flavor and body. A stock reduced by half will taste twice as rich and have noticeably more viscosity from the natural gelatin and sugars left behind.
Taken further, a stock reduced to about one-eighth of its original volume becomes what professional kitchens call a glace: a syrupy, deeply flavored liquid that solidifies when cooled. You can stir a spoonful into a pan sauce for instant body and flavor. Reduction works best with stocks, broths, wine, and fruit juices. It’s less useful for milk-based liquids, which scorch easily, or for situations where you don’t want the flavor to change.
The downside is time. Reducing a quart of stock by half takes 20 to 45 minutes depending on your burner and pan width. A wider pan exposes more surface area to evaporation and speeds things up.
Agar for Cold-Set Thickness
Agar is a seaweed-derived powder (or flake) that sets liquids into a firm gel at room temperature. It’s the plant-based alternative to gelatin. For a solid gel, like a dessert or jelly, a concentration of 1.2 to 1.5 percent works well. That translates to roughly one teaspoon of agar powder per cup of liquid. For a softer, spoonable texture, use about half that amount.
Unlike gelatin, agar must be dissolved in boiling liquid to activate. Sprinkle it into cold liquid, bring it to a full boil, and simmer for two to three minutes while stirring. It sets as it cools and holds firm even at warm temperatures, which gelatin cannot do. Agar gels are slightly brittle rather than bouncy, so they work best when you want a clean-cutting set rather than a wobbly jiggle.
How Temperature Changes Thickness
Not all thickeners behave the same way across temperatures, and this matters more than most people realize. Starch-based thickeners (cornstarch, flour, modified corn starch) actually get thicker at warmer temperatures because the starch granules absorb more water as they heat. This means a starch-thickened sauce that seems perfect on the stove may thin out slightly as it cools.
Gum-based thickeners like xanthan gum stay at a consistent viscosity regardless of temperature. If you’re making something that will be served both hot and cold, or something that sits out for a while, a gum-based thickener will give you more predictable results.
Commercial Thickeners for Medical Needs
People with swallowing difficulties (dysphagia) often need to thicken water, juice, or other thin liquids to reduce the risk of aspiration, where liquid enters the airway instead of the esophagus. Commercial products designed for this purpose fall into two categories: starch-based options like Thick-It and gum-based options like SimplyThick, which uses xanthan gum.
Research comparing the two types has found that xanthan gum-based thickeners prevent aspiration more effectively than starch-based ones, likely because they leave less residue in the throat after swallowing. Starch-based thickeners also change consistency with temperature, getting thicker in warm drinks and thinner in cold ones. Gum-based thickeners hold steady. Each product comes with specific mixing charts that match the level of thickness prescribed by a speech-language pathologist, typically labeled as “nectar thick,” “honey thick,” or “pudding thick.” Follow the product’s instructions exactly, since the ratios differ between brands.