How do you mix corn starch slurry and how do you use it?

  • Do you add the corn starch to the water, or do you add water to the corn starch?
  • Generally what proportions do you need, what is the ratio of water to cornstarch?
  • Do you need to use more slurry to thicken more liquid; if so, what is the quantity per volume?
  • 8
    One word of advice: whatever you do, once you add the slurry don't cook for too long or get too hot (do not boil). With enough heat, the starches will break down and the sauce will likely become runny again, except this time it will be runny with added corn starch flavor! Commented Nov 18, 2010 at 2:58
  • 8
    My long experience of using corn starch (or corn flour as we say in the UK) contradicts what stephennmcdonald says. You have to boil the liquid (sauce/custard/fondue) to get the starch to reach its full thickening power, and once it has, continuing to boil certainly won't make it more runny. stephennmcdonald must have accidentally curdled something (not the starch, which does not curdle).
    – PaulS
    Commented Nov 23, 2010 at 20:51
  • 2
    Agree with Paul S - you HAVE to bring it to a boil for the starches to thicken. Commented Aug 15, 2016 at 17:25
  • This article seems to reconcile the comments above -- they recommend simmering for a short time over medium heat, but not to cook too long or the starch will lose its thickening properties. Commented Nov 30, 2023 at 14:35

7 Answers 7


When making the slurry, stir cornstarch into cold water until it has the consistency of cream. This can be set aside until it's needed, but be sure to stir it briefly before you pour it into the sauce to redistribute the starch granules in the water. You should pour it into your sauce toward the end of its preparation.

According to McGee you should use roughly 2/3 as much starch as you would flour. If you aren't using a recipe, add your slurry a bit at time until it's a thick as you like it. Also remember that the sauce will thicken a bit as it cools, so it should be a little bit thinner on the stove than you intend to serve it.

  • What volume do you use per serve? I use .25 to .5 tsp per serve, with about four times that in COLD water to make slurry
    – TFD
    Commented Nov 18, 2010 at 7:22
  • I honestly never measure it :) Commented Nov 18, 2010 at 23:19

You can add cornstarch to any cold liquid, like orange juice or milk. When it's properly mixed, you can add it to the warm (hot) liquid you want to thicken.


I usually start small, with maybe a teaspoon of starch and a tablespoon of water. I guess that's roughly 2/1 water to starch by volume.

You do need more starch slurry for more liquid, but I advocate for going cautiously and starting with a single "dose" and then seeing if it's enough.

  • 2
    That would be 1 to 3 ratio
    – TFD
    Commented Nov 18, 2010 at 7:19
  • Fair enough. I can never keep the conversions straight.
    – bikeboy389
    Commented Nov 18, 2010 at 14:17

When making a slurry, I find it easier to avoid lumps by adding the liquid to the starch a little at a time. Then to use it, add a little slurry at a time to your sauce and bring it up to a bare simmer. Then add more slurry as necessary to reach the desired thickness.

Another idea if you don't care about the added fat is to make a roux with the cornstarch. Since the roux is cooked you avoid the raw starch taste. For roux, I never had any lump problems adding the starch directly to melted butter.

  • I've never had cornstarch form lumps on me. If you let a slurry stand for too long, the starch will settle out of it into an apparently solid layer, but just a little stirring will get you back to a lovely slurry. Cornstarch is really strange this way.
    – Marti
    Commented Nov 18, 2010 at 17:22
  • I'm glad you mention that settling problem because I always found that quality to be annoying. Seems like I get involved and it's "one more thing" to worry about in the midst of preparing a meal. That's why I mentioned the roux idea.
    – JGurtz
    Commented Nov 18, 2010 at 17:27

Corn starch (UK=cornflour) granules 'explode' like popcorn when heated, but on a miniature scale - this is what makes it thicken stuff (Starch gelatinization). This happens just below water boiling point (as PoloHoleSet has posted).

If you add conrnstarch slurry to liquid that is too hot, the outside grains 'pop' and form a thick sticky layer around the rest, which is one reason why you get lumps. Let the liquid cool a little before you add the cornstarch, stir it constantly, reheat it gently, don't boil it hard.


Save back a small (6-8 oz) jam or relish jar. Add your water and corn starch, tighten the matching lid and shake vigorously, voila! A perfect lump free slurry ready to pour or drizzle into your sauce.


most starches will separate from water if you let them sit. this is why a roux is used; it changes the gravity of the flour and prevents it from sinking to the bottom of the liquid where it burns

  • Unless you are recommending to make a roux from cornstarch, which is entirely unnecessary, IMO, this doesn't really respond to the question that was asked. Commented Sep 20, 2017 at 14:27

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