Baking powder and cornstarch do different jobs, so swapping one for the other will change how your dish turns out

Cornstarch thickens liquids. Baking powder makes baked goods rise. They work through completely different chemistry, so using baking powder where cornstarch belongs will leave you with a thin sauce or soup instead of a thick one—and it will taste bitter or soapy from the baking soda inside it.

If you need to thicken something right now and have no cornstarch, you have better options: flour, arrowroot powder, tapioca starch, or even mashed potato. If you need a leavening agent for baking and have no baking powder, you can make a substitute from baking soda and an acid. But baking powder cannot do cornstarch's job, and cornstarch cannot do baking powder's job.

Key Takeaways

  • Cornstarch thickens sauces and soups by absorbing liquid; baking powder makes baked goods rise through a chemical reaction.
  • Using baking powder as a thickener will leave your dish thin and add a bitter or soapy taste from the baking soda it contains.
  • Flour, arrowroot powder, tapioca starch, and potato starch all thicken liquids and work as cornstarch replacements.
  • If you need baking powder for a recipe and don't have it, you can mix baking soda with an acid like lemon juice or vinegar instead.

How cornstarch thickens, and why baking powder cannot

Cornstarch is a starch—a carbohydrate made from corn kernels. When you mix it with cold liquid and heat it, the starch granules absorb water and swell. This swelling thickens the liquid into a gravy, sauce, or pudding. The process is purely physical: heat and moisture cause the starch to expand.

Baking powder contains baking soda (sodium bicarbonate) plus an acid—usually cream of tartar—plus a filler like cornstarch. When you add liquid or heat, the baking soda and acid react and release carbon dioxide gas. Those bubbles make cakes, biscuits, and pancakes rise. Baking powder does not thicken anything. It makes things puff up.

If you stir baking powder into a sauce, the acid and baking soda will react with the liquid and release gas bubbles. You will end up with a thin, bubbly liquid that tastes bitter or soapy—not a thick sauce. The cornstarch filler inside the baking powder (usually about 20 to 30 percent of the mixture) is too small an amount to do any real thickening.

What happens if you use baking powder by mistake

The taste is the first problem. Baking soda has a strong, unpleasant flavor on its own. When it reacts with acid in your sauce, it does not disappear—it leaves behind sodium salts that taste soapy or metallic. A little bit might go unnoticed in a heavily spiced dish, but in a delicate sauce or soup, it will be obvious and unpleasant.

The texture is the second problem. Your sauce will stay thin because baking powder does not absorb liquid the way cornstarch does. You will have wasted the baking powder and ruined the dish. If you have already added it, your best option is to start over with a proper thickener, or to strain out what you can and add a real thickening agent to what remains.

Better replacements for cornstarch

If you are out of cornstarch, several other starches will thicken a sauce or soup the same way:

  • All-purpose flour: Use about twice as much flour as you would cornstarch, because flour is less concentrated. Mix it with cold water first to make a paste, then stir it into your hot liquid. Flour will make the sauce slightly opaque and add a subtle grain flavor.
  • Arrowroot powder: Use the same amount as cornstarch. It thickens at a lower temperature than cornstarch and produces a clearer sauce. It works well in acidic dishes like fruit sauces.
  • Tapioca starch: Use the same amount as cornstarch. It creates a slightly glossy, translucent sauce. Mix it with cold water first.
  • Potato starch: Use the same amount as cornstarch. It thickens quickly and produces a clear sauce, but can break down if you stir it too much or cook it too long.

All of these are starches, so they work the same way cornstarch does. None of them will add an off taste or make your dish bubbly.

If you need baking powder and don't have it

You can make a substitute for baking powder using baking soda and an acid. Mix one part baking soda with two parts cream of tartar, then use the same amount of this mixture as the recipe calls for baking powder. If you don't have cream of tartar, you can use lemon juice, vinegar, or buttermilk instead—but you will need to adjust the recipe slightly because these are liquids.

For every teaspoon of baking soda, use one tablespoon of lemon juice or vinegar, or one cup of buttermilk in place of regular milk. The acid will react with the baking soda right away, so mix the batter and bake it when ready—do not let it sit, or the bubbles will escape and your baked good will not rise.

Why the confusion happens

Some baking powder contains cornstarch as a filler, which is why people sometimes think the two are related. The cornstarch in baking powder is there to absorb moisture and keep the powder dry during storage—it has nothing to do with the leavening action. The actual rising comes from the baking soda and acid, not from the cornstarch filler.

This is also why some old recipes call for "cornstarch baking powder" or specify a brand—the amount of cornstarch filler varies, and it can affect how much leavening power you get per teaspoon. Modern baking powder is standardized, so you do not need to worry about this anymore.

Frequently Asked Questions

Can I use baking powder to thicken gravy?

No. Baking powder will make your gravy thin and bubbly, and it will taste soapy. Use cornstarch, flour, arrowroot, or potato starch instead. If you are in a hurry, flour mixed with cold water works fastest.

Will a small amount of baking powder hurt if I accidentally add it to a sauce?

A very small amount might not be noticeable in a heavily seasoned sauce, but it will not thicken anything. You will still have a thin sauce and wasted baking powder. It is better to start over with a real thickener.

Is cornstarch the same as baking soda?

No. Cornstarch is a starch that thickens liquids. Baking soda is a base that reacts with acids to produce gas bubbles. They are completely different chemicals with different jobs.

Can I use cornstarch instead of baking powder in a cake recipe?

No. Cornstarch will not make your cake rise. The cake will be dense and flat. Use baking powder, or make a substitute from baking soda and an acid.