Oil/roux temp

[Suzanne]

I was under the impression that, as when cooked with water, flour cooked with fat will also maintain its gelatinization until it has absorbed as much as it can hold. At that point (whether it's in time, temperature, or a combination of the two, I do not know), no more thickening. You're saying it's more of a gradual slide?

Actually, I just now looked it up in Understanding Baking and while I can see that I was wrong -- flour does NOT react with fat as it does with water, and even when it has absorbed all the water it can, it continues to thicken liquid with its burst starch shells -- I still don't have an explanation for the eventual loss of thickening power. Must be because cooking starch in fat affects the cells in such a way as to prevent absorption of liquid when one is added to the other.

But my question remains: at what point does cooking flour in fat prevent its gelatinization? And it is the time, temperature, or the amount of stirring the flour-fat mixture that does it? (Stirring deflates the starch shells.)

[thebighat]

Originally posted by scott123
Oven baked roux doesn't really work. It's almost impossible to get the same even color to all the flour as you do in a pan. Dry roux can be done successfully in a pan but it's about ten times harder to do well without the oil. Unless you're trying for a low fat dish, use the oil.

Not in my experience. I used to work for a French Canadian chef who had us put about two cups of clarifie in the 20 qt Hobart, then fill it up with flour and paddle it till blended. Then we toasted it in the oven. You have to watch it, and be handy with the spatula to stir it. To use it was just like using cornstarch. Working with him was really an eye-opener as far as making stocks and sauces went.

Why does this line stick in my head and where is it from.."Under heat, fat percolates through the cell walls of the starch and converts it into dextrin, a substance capable of absorbing six times it's own weight in liquid..."

[scott123]

Must be because cooking starch in fat affects the cells in such a way as to prevent absorption of liquid when one is added to the other.

Yes. Starch + browning temperature = dextrinization = loss of thickening ability

From The University of British Columbia Library Website:

"When flour is heated until brown, the starch granules undergo a process known as dextrinization. Dextrins are fragments of starch molecules composed of chains of glucose molecules. When they are dissolved in water, they have a sweet taste, and contribute to the color and pleasant flavor of brown gravies. As the starch undergoes dextrinization, it loses its thickening power."

two cups of clarifie in the 20 qt Hobart

Sorry, but when I said "oven baked roux" I meant oven baked DRY roux. Oven baked dry roux doesn't work. I've never baked a fat/flour roux.

[phatch]

The roux in clam chowder included fat for its visit to the oven.

Phil

[cooknguy]

Well, I figured it out. Tonight I made several batches of roux with different flours. I checked a couple with the candy therm. It looks like I was working between 350 and 375.

[Pete]

Suzanne, though I don't know the chemical processes behind why flour loses it's thickening ability, to answer your question, yes, it is a gradual process. As the roux gets darker (aka cooked longer) it starts to lose it's thicken capabilities. That is why gumbo, which uses a deep, dark roux for flavor needs another thickener, in the form of either okra or gumbo file.