Cornstarch substitutes, and the ratio each one needs

Ratios matter more than the choice

Almost any starch will thicken a sauce. Getting the quantity wrong is what ruins the dish, and the quantities are not intuitive.

Cornstarch is close to pure starch. Flour is only about three quarters starch, with protein and fibre taking up the rest, so it needs roughly double. Arrowroot is more concentrated, so it needs about two thirds. Swap one for another at 1:1 and you will get either a watery sauce or wallpaper paste.

Everything below replaces 1 tbsp of cornstarch.

The failure nobody warns you about

Cornstarch loses its thickening power in acid. A lemon sauce, a tomato-heavy braise, a fruit filling: all of them can turn watery after cornstarch seemed to work, because the acid breaks down the starch as it sits.

Long cooking does the same thing. Once a cornstarch-thickened sauce has been at a hard boil for a while, it starts to thin again.

Arrowroot is the fix for both. It tolerates acid, sets clear rather than cloudy, and holds. The trade is that arrowroot turns unpleasantly slimy with dairy, so it is the wrong choice for a cream sauce and the right one for a fruit glaze.

Is cornflour the same as cornstarch?

Yes. In the UK, cornflour is exactly what Americans call cornstarch: a pure, white starch used to thicken sauces. If a British recipe asks for cornflour, you can use this whole page as written. Only the name changes, so every ratio given above still applies.

The space between “corn” and “flour” matters in the US. American corn flour is finely milled cornmeal, not starch. It is used for cornbread and breading, and it will not thicken a sauce.

If you follow a British recipe with an American bag labelled “corn flour”, the sauce stays thin and can become gritty and broken. This is an easy mistake because the names look almost identical. In Britain, read cornflour as cornstarch. In America, reach for cornstarch and leave the corn flour bag for baking or breading.

Which to use for what

Gravy and stew: plain flour. It is already in the kitchen, it suits an opaque sauce, and the slight flavour it adds is welcome. Cook it out.

If the gravy is already made and thin, do not start a roux. Whisk 1 tbsp of cornstarch into 1 tbsp of cold water and stir it into the simmering gravy, which thickens about a cup in two minutes. The full set of ratios, including flour, arrowroot and the beurre manié trick for when you meant to make a roux and did not, is on how to thicken gravy. If you have cornstarch and only want to know how much, there is a calculator on how much cornstarch to thicken.

Clear or acidic sauces, fruit fillings: arrowroot.

Pies and anything freezing: tapioca. Cornstarch-thickened fillings weep after freezing and thawing. Tapioca does not.

Frying: rice flour or potato starch. Both give a crisper coating than flour, and rice flour is arguably better than cornstarch for this.

When you have time: nothing. Simmer it down. Reduction thickens and concentrates flavour at once, and costs you no ingredients. Season at the end, because it concentrates salt too.

Can you use baking powder or baking soda instead of cornstarch?

No. Neither one thickens anything, and this is the most common wrong turn on this whole topic.

Cornstarch is a thickener. It works by swelling in hot liquid. Baking powder and bicarbonate of soda, or baking soda in the US, are raising agents. They work by releasing carbon dioxide. The two do completely unrelated jobs and happen to sit next to each other in the cupboard in similar small tubs, which is almost certainly how the question started.

Put either into a sauce and you get no thickening at all, plus a soapy, faintly metallic taste that you cannot rescue. If a recipe seems to use cornstarch for lift rather than body, it is doing something else, usually keeping a cake tender by diluting the flour’s protein, and a raising agent is still not the swap.

What you actually want is in the ratio table above. Flour at twice the quantity is the answer in most kitchens.

Are cornstarch and flour interchangeable?

Not one for one, and the ratio is the whole answer: use twice as much flour. Beyond quantity, three differences matter. Flour sets opaque and matte where cornstarch sets glossy and slightly clear. Flour needs about five minutes of simmering to cook out its raw taste where cornstarch needs two. And flour-based sauces reheat and freeze better, which decides it if you are cooking ahead.

Going the other way, cornstarch instead of flour for frying is a genuinely good idea rather than a compromise. It fries lighter and crisper, and a mix of roughly half and half is what a lot of restaurant coatings use.

Thanksgiving, which is when this page gets read

Gravy is the reason most people arrive here in November, and it is the one job where running out of cornstarch is genuinely inconvenient rather than merely annoying.

If you have no cornstarch and the gravy is already made, use flour, but use twice as much and give it five minutes rather than two. Raw flour tastes like raw flour and the extra time is what cooks it out. Whisk it into cold water first, exactly as you would a cornstarch slurry.

If you have not made the gravy yet, do not reach for a slurry at all. Cook flour in the fat from the roasting tin for a couple of minutes before the stock goes in. That is a roux, it tastes of the roast rather than of stock, and no thickener added at the end gets you back to it.

Arrowroot is the trap. It works, it needs about two thirds of the cornstarch, and it sets clear and glossy. In a glaze that looks right. In a traditional roast gravy it looks like something went wrong, because gravy is supposed to be opaque. Use it for a fruit sauce and keep it away from the jug.

For pie filling, tapioca beats both. Cornstarch-thickened fruit fillings weep after freezing and thawing, which matters if you are baking ahead. Tapioca does not.

The full method for each, with the ratio for every thickener and what to do when it has already gone wrong, is on how to thicken gravy. If you have cornstarch and only need the quantity, there is a calculator on how much cornstarch to thicken.

What it costs you

Starches are close to interchangeable on macros. Per 100 g they all land between roughly 333 and 381 kcal, almost entirely carbohydrate.

The two exceptions are worth knowing. Plain flour brings about 10 g of protein per 100 g against cornstarch’s 0.3, so it is marginally more nutritious. Ground flaxseed is a different thing entirely at roughly 534 kcal, 18 g protein and 42 g fat, so it is a fibre-and-fat addition that happens to thicken rather than a like-for-like swap.

In practice you use a tablespoon or two across a whole dish, so none of this moves a per-serving number much. It is worth knowing, not worth worrying about.

Values are typical figures, rounded, and vary by brand.