Understanding Roux

Starch is a very important molecule. Plants store the energy they generate by photosynthesis as starch and pass this energy on to humans thus contributing to about 75% of our caloric intake as a population. A molecule of starch is a chain of thousands of glucose molecules linked together as either long straight chains or highly branched polymers.

In hot water, starch granules absorb large amounts of water and swell up. Eventually, the granules lose their organized structure and form a mesh-like network which creates viscosity by slowing the movement of water. So in cooking, starch is important because it acts as a thickening agent. Starch can come from grains in the form of flour, cornstarch, or rice starch, and it can come from roots and tubers in the form of arrowroot, potato starch, or tapioca.

Let's say we are trying to thicken a sauce. If we add the starch directly to the hot liquid than the molecules will stick together and make our sauce lumpy. One way to avoid this problem is to form a slurry by mixing equal amounts (by weight) of starch and cold water to disperse the granules before they are heated and start to swell. In class we made two slurries; one with cornstarch and one with arrowroot. To thicken our sauce with a slurry we would bring the sauce to a boil and slowly drizzle in the slurry while stirring. The finished sauce should be used relatively quickly because a slurry is not very stable. Two tablespoons of slurry will thicken about one cup of liquid.

A more stable sauce can be produced by thickening with a roux. Roux is made by mixing equal amounts (by weight) of butter and flour, and then cooking it to get rid of the raw cereal taste. The word roux is derived from the French word for red because as the mixture cooks it develops color (although I personally would not call it red). There are three types of roux: white, blonde, and brown. If we wanted to thicken our sauce with roux, we would melt the butter in small pot and then add the flour before the butter became too hot. We would stir the roux constantly while cooking it over medium heat and add it to our sauce when it reached the appropriate color. As the color of a roux becomes darker it starts to lose some of its thickening power and it takes on nutty and toasted flavors. Four to six ounces of roux will thicken one quart of liquid.

There are three classic "mother sauces" that are thickened with roux: Béchamel, Espagnole, and Velouté. Guess what three sauces we're making in class tomorrow?