How to Thicken Soup
Thin soup usually means not enough starch, fat, or reduced liquid, and the fix depends on what kind of soup it is. A cornstarch slurry works fast for a broth-based soup, but it will turn a delicate cream soup gluey if you're not careful, while pureeing vegetables adds body without any starch at all. Here's how to pick the right method and use it correctly.
Steps
- 1For a broth or vegetable soup, mix 1 tablespoon cornstarch with 2 tablespoons cold water into a smooth slurry, then stir it into the simmering soup and cook for 2-3 minutes until it visibly thickens and loses its raw, cloudy look.
- 2For a heartier stew or chowder, make a roux by melting 2 tablespoons butter in a separate pan, whisking in 2 tablespoons flour, and cooking for 1-2 minutes until it smells nutty, then whisk it into the soup and simmer 5 minutes.
- 3For vegetable or bean-based soups, ladle 1-2 cups of the soup (including solids) into a blender, puree until smooth, and stir it back into the pot. This adds body without diluting flavor or adding starch.
- 4For creamy soups, stir in a cornstarch slurry, or simmer uncovered for 10-15 minutes to reduce the liquid and concentrate it, since boiling dairy soups hard can cause the cream to separate.
- 5Drop in 1-2 slices of stale bread with the crusts removed, let them simmer and break down for 5 minutes, then blend the soup smooth. This is standard for classic bisques and works well when there's no cream on hand.
- 6Stir in 2-3 tablespoons of instant mashed potato flakes or a few tablespoons of cooked rice pureed with a splash of broth, both of which thicken without changing the soup's flavor much.
Common mistakes
- Adding raw flour or cornstarch straight into hot soup: it clumps instead of dissolving. Always mix it with cold liquid first to form a slurry.
- Boiling a cream-based soup hard after adding a slurry: this can cause the dairy to break and look curdled. Keep it at a gentle simmer.
- Over-thickening early: soup continues to thicken slightly as it cools, so stop just shy of the texture you want.
- Using a roux in a soup that's already finished simmering: the flour needs a few minutes of active cooking to lose its raw, pasty taste.
Equipment
- Small saucepan or skillet (for making a roux)
- Whisk
- Blender or immersion blender
- Ladle
FAQ
What's the fastest way to thicken soup without changing the flavor?
A cornstarch slurry works within 2-3 minutes and is nearly flavorless, unlike a flour-based roux, which needs to cook out its raw taste and carries a slight buttery note.
Can I thicken soup without flour or cornstarch?
Yes: puree some of the vegetables or beans already in the soup, stir in mashed potato flakes, or simmer uncovered to reduce the liquid and concentrate the flavor and texture.
Why did my soup get thinner after I added cream?
Cream and milk add richness but very little thickening power on their own. Pair dairy with a slurry, roux, or puree if the soup needs real body.
How much cornstarch does it take to thicken a pot of soup?
For about 4 cups of soup, 1 tablespoon cornstarch mixed with 2 tablespoons cold water is enough for a light thickening; double it for a noticeably heartier, chowder-like consistency.
Is it better to thicken soup with flour or cornstarch?
Cornstarch gives a glossier, clearer thickness and is gluten-free, while flour (usually as a roux) gives a matte, slightly richer body that holds up better in soups that get reheated multiple times.
Need exact temperatures or timing? Check our Time & Temperature Guide →