Dextrinizatin and Gelatinization in Sauce Making

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Assistant Cook
Feb 27, 2005

I hope someone can answer some questions I have had regarding the technical details of roux and white sauces made from them.

Before writing, I have consulted a lot of books including Culinary Institute of American and Cordon Bleu books.

1. Regarding the dextrinization of the flour, many books say cooking the starch in fat reduces "starchiness" and increasdes "nuttiness". But if I understand it correctly at least for a white or blond roux, dextrinization will not be complete and so most of the starch will still be there. So does the nuttiness from dextrinization partially mask the starch flavor of the remaining starch or is something else happening at a chemical level which actually changes the starch flavor and aroma of all the starch molecules?

2. Other books I have read say that in sauces made from rouxs, gelatinization further reduces starchiness by spreading the starch molecules around but I haven't read anywhere that it changes them chemically. So does the spreading around of the molecules reduce starchiness by effectively "diluting" their starch flavor? Or does it not change starch flavor at all, just the texture?

3. Some books mention that when making a bechamel, you should whisk and simmer (for up to 30 minutes) to reduce starchiness . I have had pretty good luck simmering at low heat and whisking only several minutes following gelatinization. Doesn't oversimmering of dairy-based sauces begin to produce off-flavors from cooking the milk proteins?

4. Finally, many books seem to specify adding a hot roux to a cold liquid (or vice-versa). But does this matter if you add only small amounts of liquid to the roux? My method for 1 to 3 cups of bechamel has been to add only a couple tablespoons of liquid to the roux in the beginning (without regard to what is hot or cold), mix till no lumps, than add slighly more liquid. I don't usually have any lumps.

Thanks so much,



Executive Chef
Aug 25, 2004
USA, Oklahoma
I think the only answer I can give you, is that the "nutty" flavor of a cooked roux increases as you take the roux darker and darker. In Cajun cooking, some rouxes are cooked so dark they are almost black. These dark rouxes tend to have a more pronounced "nutty" flavor, while also having less ability to thicken a liquid.

Michael in FtW

Master Chef
Moderator Emeritus
Sep 5, 2004
Fort Worth, TX

I didn't want you to think that your question has been ignored ... it's just not a simple one to answer, as you've noticed from the answers you have received to the same question posted on other cooking forums. And the more I tried to find a simple answer, the harder it got.

Dextrinization is apparently not necessary for either gelatinization or reduction of "raw starch" flavor. For example, you can reduce the "raw" flavor in a water/flour slurry, or a beurre manie, by cooking the starch for a while. What the slurry and beirre manie does is coat the starch ganules so they they have greater dispersability in the liquid - to that they don't clump together and form a water-tight seal around clumps of granules (aka: lumps). One of the problems with the starch in four is cellulose that surrounds the starch granules. When it get's wet it get's sticky ... and it's not very water soluable.

Starch is a long chain of glucose molecules .... dextrinization is a breakdown of these long chains into shorter (usually) 3-5 molecule chains of sugars (dextrins). When you make a roux - the darker it gets the greater the dextrinization ... and inversly the lower the gelatinization ability since the starch chains have been reduced. Ironically, the color and flavor are probably due to a Maillard browning reaction (since we are dealing with proteins and sugars in the flour) ... and one of the characteristics of Maillard browning reactions and a colored roux is a "nutty" flavor.

As for the magic chemical reaction that causes a change in flavor ... it might be no more complex than allowing time for the starch granuals to hydrate and change from a straight chain into a helix configuration, under heat. This would change the way they bond to other molecules - thus altering flavor.

Another factor is the permeability of the starch granules. The cellulose capsule around the starch granules is not very water soluable ... but it is fat soluable ... thus in making a roux you "soften" up the cellulose and start the hydration process. Hydration is slow at first ... and with time and heat the rate increases.

Regarding your bechamel question ... do whatever works for you. I generally make mine in a double-boiler and don't whisk constantly. However, I have found that time and temp can make a difference texture - but little in flavor.

The hot roux to cold liquid, or hot liquid to cold roux, is a rule begging to be broken. It depends on what you are doing. When I make beef stews ... I don't flour the meat before searing, I don't add flour and essentially make a roux after adding the meat back to the pot .... when the stew is done I make a roux in a seperate saute pan and add the hot roux to the simmering stew ... and then cook it for about 3 minutes ... no muss, no fuss, no lumps (knock on wood).

Oh, regarding the milk proteins .... knew there was something I was missing. You can scourch them (mainly the milk solids which are more than just proteins) ... which will cause bitterness. Cooking them at a lower temp you can cook them just about all day without a problem.

As someone on another forum suggested, go to the library, or purchase, and read Shirley Corriher's Cookwise, and Harold McGee's On Food and Cooking (Revised Edition). I would also add to this the 1995 Scribner edition of Irma Rombauer's classic, Joy of Cooking.

I, like you, like to know how things work. But sometimes, it's possible to get so caught up in the "micro-molecular" workings that it becomes almost impossible to understand without a PhD in Chemistry - and doesn't alter the tried-n-proven techniques.

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