How to Thicken (or Thin) a Sauce
Updated August 15, 2026
To thicken a sauce: reduce it (simmer uncovered — best flavor, takes time), whisk in a cornstarch slurry (fastest), add beurre manié (butter kneaded with flour, for richness), or mount with cold butter off the heat (for pan sauces). To thin one, add the sauce's own base liquid — stock, milk, or pasta water — a splash at a time.
| Method | Speed | Best when |
|---|---|---|
| Reduction | Slow | There's time; flavor concentration is welcome |
| Cornstarch slurry (1 tbsp + cold water per cup) | Seconds | Stir-fries, gravies, anything glossy, tonight |
| Beurre manié (equal butter + flour, kneaded) | 1–2 min | Finished braises and stews needing body |
| Butter mounting (cold cubes, off heat) | 1 min | Pan sauces — gloss and richness, mild thickening |
| Purée a ladleful of the solids | 2 min | Bean soups, vegetable stews — no added starch |
| Egg-yolk liaison (tempered) | Careful | Velvety cream sauces; never boil after |
Pick by what the sauce can afford
Reduction costs time and concentrates everything — including salt, so season after reducing, not before. Starch costs clarity of flavor a little; cornstarch reads glossy-Chinese-takeout, flour reads gravy (details in the cornstarch vs. flour guide). Butter costs nothing but calories and must stay off the boil or it separates. The purée trick is the sleeper: a blended cup of the soup's own beans or vegetables thickens with zero new ingredients.
Thin sauces are usually under-reduced rather than over-liquid — before adding a thickener, try five more minutes of honest simmering.
Thinning without dismantling
Match the thinner to the base: stock into gravies and braises, milk or cream into white sauces, pasta water into anything that'll meet noodles (its starch keeps the emulsion together), plain water only when nothing else fits — it dilutes flavor along with texture. Add small splashes over heat and let it come back together between additions; a sauce over-thinned in one pour needs re-thickening, and now you're commuting in both directions.
Quick answers
- What's the fastest way to thicken a sauce?
- A cornstarch slurry — 1 tablespoon cornstarch in cold water per cup of sauce, streamed in at a simmer. Thick in under a minute.
- How do I thicken a sauce without flour or cornstarch?
- Reduce it, mount it with cold butter, or purée some of its own solids back in. Cream also thickens as it reduces.
- Why did my sauce get thin again after thickening?
- Cornstarch breaks down with prolonged boiling or acid, and amylase in saliva (a tasted-then-double-dipped spoon) genuinely liquefies starch-thickened sauces. Rethicken with a fresh half-slurry.