Cornstarch has about twice the thickening power of flour: use 1 tablespoon cornstarch in place of 2 tablespoons all-purpose flour. Cornstarch is pure starch from corn, gives glossy, translucent sauces and is naturally gluten-free. Flour makes opaque sauces and contains gluten. In the UK, cornstarch is called cornflour.
Key facts
- 1 tbsp cornstarch thickens like 2 tbsp all-purpose flour (University of Kentucky, Utah State and Colorado State extensions).
- Mix cornstarch with cool liquid first (a slurry), then stir it into hot liquid and boil about 1 minute.
- Acid weakens cornstarch, and cornstarch-thickened dishes don't freeze well; arrowroot and tapioca handle both better.
- Pure cornstarch is naturally gluten-free. FDA allows a "gluten-free" label only below 20 parts per million gluten.
- US cornstarch = UK cornflour. US corn flour is finely ground whole corn, a different product.
What is cornstarch made from?
Cornstarch is made from the starchy part of the corn kernel. Beyond Celiac describes it as coming from the starchy portion of the grain, and University of Kentucky Cooperative Extension calls it a pure starch derived from corn.
All starch thickeners work the same basic way. Starch granules absorb liquid and swell as they heat, and Kentucky Extension notes they begin thickening at around 140°F (60°C). Flour contains starch too, but it is also part protein, which dilutes its thickening power.
Cornstarch vs flour: what's the difference?
Cornstarch is a pure starch that thickens about twice as strongly as flour and gives a clearer sauce; flour is milled wheat that thickens more gently, turns sauces opaque and contains gluten. Each has jobs it does better.
| Cornstarch | All-purpose flour | |
|---|---|---|
| Made from | Starchy part of corn | Milled wheat (starch + protein) |
| Thickening power | About 2 times flour | About half of cornstarch |
| Look of the sauce | Glossy, translucent | Opaque, matte |
| Cooking to lose raw taste | About 1 minute at a boil | About 3 minutes at a boil |
| Usual method | Slurry with cool liquid | Roux (cooked in fat) or slurry |
| Freezes well? | No | Not specified by our sources |
| Gluten | Naturally gluten-free | Contains gluten |
Cooking times are from University of Kentucky Cooperative Extension. Pick cornstarch when you want a clear, shiny finish or a gluten-free sauce, and flour when an opaque sauce is fine and you're already cooking in fat.
How much cornstarch replaces flour?
Use half as much cornstarch as flour: 1 tablespoon cornstarch replaces 2 tablespoons all-purpose flour as a thickener. Going the other way, use 2 tablespoons flour per tablespoon of cornstarch and cook it a little longer (weights: all-purpose flour cups to grams). University of Kentucky, Utah State and Colorado State extensions all give this 1:2 flour to cornstarch ratio.
Replacing flour with cornstarch only works for thickening. Cornstarch has no gluten to build structure, so it can't stand in for flour in bread, cake or cookie dough cup for cup. Our cornstarch substitutes page lists more swaps, and cornstarch cups to grams gives weights (USDA lists 1 cup at 128 g).
How to make a cornstarch slurry
A slurry is cornstarch stirred into a small amount of cool liquid before it goes into a hot pot. Kentucky Extension warns that adding starch straight to hot liquid makes lumps, because the outside of each clump gels before the inside gets wet.
- Stir the cornstarch into a few tablespoons of cold water, broth or other cool liquid until completely smooth.
- Bring the sauce, soup or gravy to a simmer.
- Stir the slurry again (cornstarch settles fast), then pour it in while stirring.
- Bring to a boil and cook about 1 minute, stirring gently, until thickened and no longer chalky.
- Stop once it's thick. Long, hard stirring can thin it back out.
This is also how to thicken soup with "corn flour" in a UK recipe, since UK cornflour is cornstarch. A tablespoon is 1/16 cup; see tablespoons in a cup.
Roux vs slurry: can you make a roux with cornstarch?
A roux is flour cooked in fat, such as butter or pan drippings, before liquid is whisked in; a slurry is starch mixed with cold liquid. Because the flour is mixed into fat before any liquid goes in, it disperses without the clumping you get from dumping dry flour into hot liquid, and the cooking time helps lose the raw flour taste.
Cornstarch is almost always added as a slurry instead. Because it thickens quickly and needs only a short boil, there's little reason to cook it in fat first, and adding it near the end gives more control. If you need gluten-free gravy, a cornstarch slurry stirred into the simmering drippings and broth is the simplest route. Store leftover gravy as described on our gravy storage page.
One difference to plan for: Kentucky Extension notes flour-thickened sauces keep thickening as they cool, so take flour gravy off the heat just before it reaches the texture you want.
When does cornstarch or flour fail?
Starch thickeners break down with acid, too much heat or stirring, and freezing. Knowing which thickener tolerates which problem saves a runny sauce:
- Acid. Kentucky Extension says acidic ingredients such as lemon juice, wine and vinegar reduce thickening, and cornstarch handles acid poorly. Arrowroot works well with acidic ingredients.
- Freezing. Kentucky Extension says cornstarch is not suited to dishes you plan to freeze. Tapioca pie fillings don't weep after freezing and thawing, and arrowroot freezes well.
- Overcooking and overstirring. Heat and agitation both reduce thickening. Cornstarch tolerates fairly long cooking before it breaks down, while arrowroot can lose its power at high heat, so add arrowroot near the end.
Is cornstarch gluten-free?
Yes. Pure cornstarch is naturally gluten-free, because corn does not contain the gluten proteins found in wheat, barley and rye. Beyond Celiac lists cornstarch as gluten-free in its natural form but warns that cross-contact can happen during manufacturing, so people with celiac disease should check labels.
FDA's gluten-free labeling rule, issued in 2013 (21 CFR 101.91), lets a food carry a "gluten-free" claim only if any unavoidable gluten is below 20 parts per million. Foods that are naturally free of gluten can use the label, but the 20 ppm limit still applies. Anyone managing celiac disease should follow their doctor's or dietitian's advice.
Tapioca, arrowroot and potato starch also don't come from wheat, barley or rye; the same label advice applies.
Is cornstarch the same as corn flour or cornmeal?
No, though the names depend on where you live. In the US, cornstarch, corn flour and cornmeal are three different products. In the UK, "cornflour" means cornstarch; Oxford's dictionary labels cornflour as the British word for what North Americans call cornstarch. Maize starch is another name for cornstarch.
| Product | What it is | Used for |
|---|---|---|
| Cornstarch (UK: cornflour) | Pure starch from the corn kernel; fine white powder | Thickening sauces, gravies, puddings, pie fillings |
| Corn flour (US) | Ground corn, very fine: FDA's standard for white corn flour requires at least 98% to pass a No. 50 sieve | Baking and breading, not thickening |
| Cornmeal | Ground corn, coarser: FDA's standard for white corn meal requires at least 95% to pass a much larger No. 12 sieve | Cornbread and coatings |
US corn flour and cornmeal are ground corn rather than extracted starch, so they don't thicken like cornstarch. If a British recipe says cornflour to thicken gravy, reach for cornstarch. See cornmeal cups to grams for weights.
Tapioca, arrowroot and potato starch vs cornstarch
Tapioca, arrowroot and potato starch are all pure starches that can replace cornstarch, but each behaves a little differently. University of Kentucky Cooperative Extension gives these amounts to match 2 tablespoons of flour:
| Thickener | Amount equal to 2 tbsp flour | Made from | Strengths | Weak spots |
|---|---|---|---|---|
| Cornstarch | 1 tbsp | Corn | Strong, glossy, tolerates longer cooking | Acid, freezing |
| Tapioca | 1 tbsp | Cassava root | Crystal-clear, thickens fruit juices fast, freezes without weeping | Jelly-like texture |
| Arrowroot | 1 tbsp + 1 1/2 tsp | Arrowroot plant root | Clear, smooth, works with acid, freezes well, thickens at lower heat | Can thin at high heat; may curdle milk-based cream sauces |
| Potato starch | 1 1/2 tsp | Potatoes | Thickens quickly, neutral flavor | Very strong, so use sparingly |
Other extension charts round these differently. Utah State and Colorado State treat cornstarch, potato starch and arrowroot as equally strong (1/2 tablespoon each per tablespoon of flour), and Colorado State lists 1 tablespoon arrowroot for 1 tablespoon cornstarch. Treat any swap as a starting point and add more slurry if needed.
Tapioca flour vs tapioca starch
They are the same thing. Kentucky Extension describes tapioca as pure starch from cassava root, sold as tapioca flour or as pearls. Quick-cooking (granular) tapioca is different in texture; Utah State uses 2 tablespoons granular tapioca for each tablespoon of cornstarch in fruit pies.
Is baking powder the same as cornstarch?
No. Baking powder is a leavener made of baking soda, a dry acid and a little starch. Cornstarch on its own has no leavening power, and baking powder is not a thickener, so neither can stand in for the other. See baking soda vs baking powder for how leaveners work.
Questions people ask
Is cornstarch the same as flour?
No. Cornstarch is pure corn starch with about twice the thickening power of wheat flour, and it's gluten-free. Use 1 tablespoon cornstarch in place of 2 tablespoons flour for thickening.
Is cornflour the same as cornstarch?
In the UK, yes: cornflour is the British name for cornstarch. In the US, corn flour is finely ground whole corn and won't thicken the same way.
Does cornstarch have gluten?
Pure cornstarch is naturally gluten-free. Cross-contact can happen in processing, so look for a gluten-free label, which FDA allows only below 20 ppm gluten.
Is arrowroot the same as cornstarch?
No, but it's a close substitute. Arrowroot gives clearer sauces, handles acid and freezing better, and should be added near the end of cooking.
Can you thicken gravy with cornstarch instead of flour?
Yes. Mix 1 tablespoon cornstarch with cold water for each 2 tablespoons of flour the recipe calls for, stir it into the simmering liquid, and boil about 1 minute.
Is cornstarch the same as cornmeal?
No. Cornmeal is coarsely ground whole corn used for cornbread and coatings; cornstarch is the extracted starch used for thickening.
Sources
- University of Kentucky Cooperative Extension: Cooking with starches
- Utah State University Extension: Ingredient substitution (FN 255)
- Colorado State University Extension: Ingredient substitutions (Fact Sheet 9.329)
- Beyond Celiac: Is corn gluten-free?
- eCFR: 21 CFR 101.91, Gluten-free labeling of food
- FDA: Gluten-free labeling of foods
- eCFR: 21 CFR 137.211, White corn flour
- Oxford Learner's Dictionaries: Cornflour
