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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?
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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! – stephennmcdonald Nov 18 '10 at 2:58
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 Nov 23 '10 at 20:51
up vote 4 down vote accepted

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.

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That would be 1 to 3 ratio – TFD Nov 18 '10 at 7:19
Fair enough. I can never keep the conversions straight. – bikeboy389 Nov 18 '10 at 14:17

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.

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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.

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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 Nov 18 '10 at 7:22
I honestly never measure it :) – Michael Baker Nov 18 '10 at 23:19

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.

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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 Nov 18 '10 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 Nov 18 '10 at 17:27

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