Does Baking Powder Really Thicken Sauce?
If your sauce turned out too runny, you may have heard that mixing in some baking powder can easily thicken it up. But just how effective really is this food hack? According to Our Everyday Life, baking powder does do the job in a pinch, but it's not the first ingredient you should reach for. The reason is that baking powder doesn't function primarily as a thickener, it just happens to have a thickening agent in it — cornstarch. Baking powder consists of sodium bicarbonate and one or more acid salts, which acts as a leavener for baked goods when combined, but cornstarch is only a secondary ingredient.
When you add baking powder into sauce, the active ingredients will react with the liquid and heat in the same way they would if they were added into a cake batter. The cornstarch in it will cause your sauce to thicken in the process, but too much sodium bicarbonate will also contribute a bitter taste. Therefore, if you're planning to add baking powder to your sauce, doing so in moderation is essential unless you want the flavor to change.
Try cornstarch to thicken your sauce instead
Given that baking powder only works as a thickener because of the cornstarch in it, it makes more sense to just use plain cornstarch. This way you'll have better control over the consistency without worrying about the other ingredients in the baking powder that could make your sauce taste bitter.
According to The Spruce Eats, the best way to add cornstarch to a sauce is to make a slurry. For each cup of sauce, you'll need one tablespoon of cornstarch and an equal amount of liquid. Mix both together until there are no clumps, then whisk it in the sauce. To cook away the starchy aftertaste, bring the sauce to a boil and let it simmer, but don't overcook it, otherwise the starch will break down and lose its effectiveness.
As Modern Mom explains, the same method applies if you're using baking powder, but you can't be as liberal with the amount you use, and you'll need to simmer it over low heat instead of bringing it to a boil. If your sauce is really that watery, cornstarch is a safer bet, but technically, baking powder will work, too.