How to thicken liquids

[JoshRountree]

My mom has always used a roux to thicken liquids, but I have recipes and have seen others use corn starch. Can anyone tell me the difference and when to use one or the other?

And, what are the techniques for both. I've got the reux down pretty good. I melt butter, add flour, cook a little, and add batches of whatever liquid I want until it reaches my desired consistency. Then I add it to whatever I want to thicken. I don't know about corn starch though. I've read that you add equal parts cold water and corn starch and just mix that with whatever you want to thicken, but haven't tried it.

Thanks for any info.

Edited February 14, 2008 by JoshRountree (log)

[cathrynapple]

Cornstarch has more thickening power than flour. It also allows your thickened liquid to stay transparent. It won't be cloudy like a roux-based liquid. You can also use cornstarch if you're conserving calories.

If you're adding cornstarch, mix it with some cold water and pour it into an almost boiling liquid. Let it bubble for a minute or two to thicken properly.

[JoshRountree]

Cornstarch has more thickening power than flour. It also allows your thickened liquid to stay transparent. It won't be cloudy like a roux-based liquid. You can also use cornstarch if you're conserving calories.

If you're adding cornstarch, mix it with some cold water and pour it into an almost boiling liquid. Let it bubble for a minute or two to thicken properly.

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Does a roux add flavor where cornstarch wouldn't?

Edited February 14, 2008 by JoshRountree (log)

[paulraphael]

They will give different appearances and different consistencies. Brown roux adds toasted flavors, depending on how much you brown the flour (the thickening power of the flour declines the more it browns). Blonde roux doesn't have any significant flavor. Roux is a lot more time consuming to use, because fat needs to be rendered out and skimmed. But it's a more stable thickener; high heat will break down the corn starch much faster than the flour starch.

You can also add flour at the end (beurre manié) by kneading flour into an equal weigh of butter and stirring it in right before serving. This is fast, but the mixture can't be cooked after it's added (flour is flavorless when it's raw and when it has all the cereal flavors cooked out of it; but when it's cooked a little, it tastes bad)

Arrowroot is another option; I use it more than the other starches. Flavorless, works in small quantities, can be added at the end, and is more temperature stable than corn starch. Will give a slightly different texture/appearance than other starches. Just don't use too much ... it can get a little too glossy and slick.

Edited February 14, 2008 by paulraphael (log)

[John S.]

I agree with paulraphael in that arrowroot is very easy to use. You can use it for your clearest recipes and it imparts no color or flavors to anything. However I don't use it for gravies, where I want a flour/fat roux to flavor the batch.

John S.

[cathrynapple]

I also think a roux-thickened dish has a rounder, richer taste. A cornstarch-thickened dish will be almost gelatinous.

[HungryC]

I'm partial to rouxs as thickeners, but I'm a cajun, genetically programmed to make roux! Cornstarch is okay for chinese sauces & coatings/sauces, but I dislike the jellied texture that results when it is used in a mostly liquid dish (soups, stews, gumbos, etc). Cornstarch adds nothing to a dish's flavors, while a roux (depending on the depth of browning) adds color, nuttiness, and toasty brown undertones. You can use buerre manie (butter and flour kneaded together) when you want to thicken, but don't want those browned flavors. (Edited: sorry to repeat some of what Paul wrote, I was skimming..)

Edited February 14, 2008 by HungryC (log)

[paulraphael]

I don't use it for gravies, where I want a flour/fat roux to flavor the batch.

Yeah, I don't think I'd want to use arrowroot get anything as thick as a traditional gravy. It would be kind of strange (gelatinous in the way cathrynapple describes).

I like it to add just a bit of thickness, to get a brothy sauce to cling to the food. Or else in conjunction with a non-starch thickener, like the gelatin in a moderately reduced stock.

[conor610]

Why/how would one skim the fat out of a roux-thickened liquid? I make roux all the time, and I never get a skim of fat on top--doesn't the butter disperse evenly through the liquid, since it's so thoroughly mixed with the flour? Plus, I only use roux to thicken liquids that I want to have richness--so even if I somehow COULD render the fat out, I never WOULD...

[paulraphael]

Why/how would one skim the fat out of a roux-thickened liquid?  I make roux all the time, and I never get a skim of fat on top--doesn't the butter disperse evenly through the liquid, since it's so thoroughly mixed with the flour?  Plus, I only use roux to thicken liquids that I want to have richness--so even if I somehow COULD render the fat out, I never WOULD...

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Well, when you make a roux thickened brown sauce, typically fat rises to the surface along with white scum (which includes, among other things, milk proteins). The only way the fat can get dispersed in the liquid is if it gets emulsified. Maybe if you're making something like a gumbo, with things like file powder or okra, they can serve as emulsifiers and bind the fat into the liquid. With sauces like bechamel the milk or cream is an emulsion and can bind smoothly with the butterfat. But with a brown sauce, it typically only happens if the stock is allowed to boil, in which case the fat can be broken up into tiny globules and stay bound up in the liquid, along with small protein particles. The result isn't richness ... it's a muddy, cloudy, greasy stock.

So it's customary to bring roux thickened brown sauce to a very light simmer, and to skim them constantly to remove the scum and the fat from the top. One reason that non-roux brown sauces (made from reduced bone stock) have become popular in restaurants is that they need much less skimming while they simmer away.

Edited February 15, 2008 by paulraphael (log)

[TheSwede]

When using roux, you add fat to the liquid. That will affect the taste and viscosity in itself.

You can of course add some butter to your cornstarch thickened liquid too. The result won't be the same as with roux, but probably more similar than when comparing roux to plain cornstarch.

[s_sevilla]

If used in very very small additions, Xanthan Gum is also a phenomenal thickener. Be wary, however, as if you want to thicken something a lot, the Xanthan will give you a slimy consistency, but in moderation it provides a clear, absolutely tasteless method of improving the body of a sauce. It's surprisingly easy to find in your local health-nut shop because it is extremely useful for vegan cookery and those with gluten sensitivity.

[TheSwede]

Xantan is on my "must buy" list, especially since it works equally well on hot and cold liquids.

I bet it is cheaper in the local health shop than from the El Bulli Texturas brand... Any online sources (especially in Europe)?