Viscosity. Thickeners. Starch. And why French mother sauces “roux” the world.
1-Minute NomNom
There are five mother sauces in French cuisine: Béchamel, Espagnole, Velouté, Tomate, and Hollandaise. They are the five “building blocks”, and all other sauces are “extended relatives of these five”. Preparing these well is a mark of a skilled hand. Take a look for example, at this short clip from the movie The Hundred Foot Journey:
Of the five sauces, Hollandaise is unique in that it is an emulsion (of egg yolks, butter, water and lemon juice – see the 1-Minute NomNom “Cooking gold”). The other sauces –Béchamel, Espagnole, Velouté, Tomato — all start with a roux (pronounced as “roo”).
Roux is a thickener made with flour and fats (usually butter). For example, take a look at that thick savory sauce that we have layered in between the sheets of pasta, meat, vegetables and cheese in lasagna. That is in fact Béchamel, which is made with milk thickened with roux.
Roux increases the viscosity of any mixture, giving us the familiar texture of thickened sauces. This viscosity comes from the starch within the flour (see item 6 in the diagram of a plant cell, don’t worry about the rest).
During cooking, the starch granules take in water. They swell and, according to Harold McGee, at around 50-60°C/120-130°F, they “suddenly lose their organized structure, absorb a great deal of water, and become amorphous [i.e. gel-like] networks of starch and water intermingled.” This is starch gelatinization, which starts to thicken the sauce.
With continued cooking, the starch granules eventually burst, leaking amylose and amylopectin. Because amylose are long straight-chained molecules, they line-up and cross-link more easily. They thus become entangled with each other readily. Amylopectin, on the other hand, has branches that prevent the molecular chains from being packed tightly together.
This is not exactly how it looks like, but it is a good way to visualize the gel-like 3D-fishnet, so that the concept is now more tangible and easier to grasp (pun intended).
Think of the entangled amylose chains as a fishing net. Harold McGee dsecribes it as:
“long amylose molecules form a… three-dimensional fishnet that … entraps pockets of water, but blocks the movement of the… water-swollen starch granules.”
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As a rough analogy, imagine a fishnet of small and large balloons, and the different balloons are filled with either water or gels (because of the starch gelatinization described earlier). The mix of water and gels gives roux and sauces made from it its viscous and paste-like texture.
While Béchamel is made with roux and milk, Espagnole is made with veal stock, Velouté with chicken or fish stock, and Tomato with tomatoes (though some chefs choose not to use roux). You might also have noticed that the colors of each of these sauces take after the stock that is used.
Roux rules!
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