On Flour vs Cornstarch as a thickener

[Suzanne]

On the Cooking Questions board here, we just had someone ask about the relative uses and merits of flour versus cornstarch as a thickener. I directed the members to pages 610 to 620, Sauces Thickened with Flour and Starch. For those who may not have the book (shame on them!), would you please give a little of the information there? Thanks.

[Harold McGee]

Sure. Cornstarch is pure starch, while flour is on the order of 10% protein. Doesn’t sound like much, but that’s enough to make whatever you’re thickening opaque instead of translucent. Pure starch is also a more efficient thickener than flour, meaning you need less to get the same consistency. And corn starch is made by wet-milling corn, while flour is made by dry-milling wheat: so the flavors are different as well.

Harold

[chefsandra]

Hello - Where does Arrowroot fall in the Flour vs Cornstarch "debate"? Are there certain recipes where you would definitely prefer arrowroot to cornstarch?

Thanks,
Chef Sandra

[epol29]

Is there a difference/preference for using corn or potato starch? Thanks, Eve

[Harold McGee]

Arrowroot and potato starches come from below-ground storage organs, cornstarch and flour from seeds, and the two different kinds of sources produce starches with different qualities. Briefly, the root starches have larger granules and longer starch molecules that gelate and thicken at lower temperatures, and are more efficient at thickening, but that break down on prolonged heating or freezing: so you need less root starch to thicken, but the consistency isn’t as stable. Root starches also have a more neutral flavor than seed starches.

Harold