The quick answer
For a quick light thickening, mix 1 teaspoon cornstarch with 2 teaspoons cold water per cup / 240 ml of soup, stir into simmering soup and cook briefly until thickened. Add gradually. For a fuller texture without extra starch, blend a portion of cooked vegetables or beans and stir it back in.
In this guide
Decide what kind of texture you want
A clear broth, creamy purée and chunky stew need different solutions. Blending makes soup opaque and changes the shape of its ingredients. Reduction preserves the ingredient list but concentrates salt as water evaporates. A slurry can keep more pieces intact while giving the liquid body.
Taste before adding anything. If the soup is already salty, reducing it is a poor first choice. Choose blending or a carefully measured thickener instead, and adjust the seasoning only after the final texture is reached.
Use a cold cornstarch slurry
Estimate the amount
For light body, start with 1 teaspoon cornstarch per cup / 240 ml of soup. For 4 cups / 960 ml, that is 4 teaspoons. This is a starting amount; existing starch and ingredients change the result.
Mix separately
Combine the starch with twice its volume of cold water until smooth. Stir it again just before using because starch settles. Do not scatter dry cornstarch straight into hot soup.
Add gradually
Bring the soup to a gentle simmer and pour in some slurry while stirring. Cook briefly until the liquid thickens, then assess before adding more.
Recheck before serving
A boiling-hot soup feels thinner than the same soup after it cools slightly. Spoon out a little, let it cool and decide whether the texture suits the dish.
Thicken with ingredients already in the pot
Mash some tender potato, beans or lentils into the liquid, or blend a portion and return it to the pan. Keep enough whole pieces for the texture you want. With a countertop blender, follow its hot-liquid instructions and avoid overfilling or sealing in steam.
A butter-and-flour paste or cooked roux can work for flour-friendly soups, but the flour needs adequate cooking. Cream adds richness more reliably than substantial thickening, and dairy can separate in acidic soup at high heat.
When soup becomes too thick
Add water or suitable unsalted stock a little at a time. Bring the soup back to its serving temperature and taste again before salting. If a slurry leaves lumps, stop adding it; carefully strain or blend the affected liquid if that suits the soup.
Cornstarch is called cornflour in the UK. Fine cornmeal is a different ingredient. Check the packet and allergen requirements when using flour, cream, bread or any packaged thickener.
A few useful answers
Can I thicken soup without flour or cornstarch?
Yes. Blend cooked potato, beans, lentils or other suitable ingredients from the soup and stir them back in.
Will reduction fix every thin soup?
No. It concentrates flavor and salt, and can overcook ingredients. Choose it only when that tradeoff suits the dish.
Use the full recipe alongside these tips, and follow the stated care and safety limits of your equipment.
