Vol. XXII · Stocks, Soups and Sauces Plate 6 of 11roux, white roux, blond roux, brown roux, dark roux, Cajun roux, gumbo, flour, butter, thickening power, dextrinisation, 油面糊, 炒面MT

Roux.

A gumbo's chocolate-brown roux takes an hour of stirring and thickens barely a quarter as well as a pale one. The cook pays in thickening for flavour.

Raw flour stirred into hot liquid forms lumps: the outside of each clump gelatinises into a skin that keeps water from the dry flour inside. Cooking the flour first in an equal weight of fat solves this: each particle is coated in fat, so it disperses evenly when liquid is whisked in, and the starch swells separately (VII.1). Cooking also takes away the raw, cereal taste. A white roux is cooked a couple of minutes without colour, a blond roux until it smells of biscuits, a brown roux until it is the colour of peanut butter, and a dark Cajun roux for 45 minutes or more until it is the colour of chocolate.

Colour costs thickening. As the roux browns, heat breaks starch into shorter chains (dextrins) that can no longer swell and tangle, and browning reactions (VIII.1) use up some of it too; a brown roux has roughly a half, a dark one perhaps a quarter, of a white roux's thickening power. So brown sauces and gumbos either use much more roux, or get their body elsewhere — reduction, gelatin, okra, filé. The workshop browns a roux.

Below: the colour of a roux and its remaining thickening power against minutes of cooking at about 160 °C (teaching curves), and the grams of flour needed per 250 mL for a coating sauce at that colour (the square law of VII.2).

What you will learn
Workshop
Teaching curves shaped on published comparisons: colour = 1 − exp(−minutes ÷ 15); thickening power = 1 − 0.75 × colour, so a dark roux keeps about a quarter. Flour for a coating sauce = 15 g per 250 mL ÷ thickening power (from the index of VII.2).

Pale for thickness, dark for flavour

On these teaching curves a white roux cooked two minutes needs about 17 g of flour per 250 mL to coat a spoon; a brown roux cooked 15 minutes about 29 g; a dark roux cooked 45 minutes about 52 g. Gumbo cooks therefore make a lot of roux, and many add a little pale roux or another thickener at the end. Clarified butter or oil is used for long-cooked roux, because whole butter's milk solids burn (IX.5).

Method: use equal weights of fat and flour; heat the fat, add the flour, and stir constantly over moderate heat with a flat-ended spoon, scraping the corners; stop at the colour you want, and if black specks appear, it has burnt — start again, because burnt roux makes the sauce bitter (VIII.8). Roux can be made ahead and kept in the fridge. Combine with liquid as in XXII.5: one hot, one cool, whisking. Chinese 炒面 (dry-fried flour) and Indian roasted besan are flour browned without fat, used the same way for flavour and gentle thickening.

At the stove

Cook four spoonfuls of roux to white, blond, brown and dark. Thicken the same amount of stock with each and compare thickness and taste.

The roux came into French cooking in the seventeenth century, replacing breadcrumbs as the standard thickener; in Louisiana, Cajun and Creole cooks took it to the dark extreme for gumbo and étouffée, where "first you make a roux" is the opening line of countless recipes.

Terms

Roux
Flour cooked in an equal weight of fat, used to thicken sauces.
Dextrins
Short starch fragments formed by dry heat; they thicken poorly.
Clarified butter
Butterfat without milk solids (IX.5).
Gumbo
A Louisiana stew thickened with dark roux, okra or filé.
Roux coats flour in fat so it thickens without lumps. The darker it cooks, the nuttier it tastes and the less it thickens: a dark roux needs several times the flour of a white one.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.