On Food and Cooking

disperse in a hot liquid, roux making has three
other useful effects on the flour. First, it cooks
out the raw cereal flavor and develops a
rounded, toasty flavor that becomes more
pronounced and intense as the color darkens.
Second, the color itself — the product of the
same browning reactions between
carbohydrates and proteins that produce the
toasty flavor — can lend some depth to the
color of the sauce.
Finally, the heat causes some of the starch
chains to split, and then to form new bonds
with each other. This generally means that
long chains and branches are broken down
into smaller pieces that then form short
branches on other molecules. The short,
branched molecules are less efficient at
thickening liquids than the long chains, but
they’re also slower to bond to each other and
form a continuous network as the liquid cools.
The sauce is therefore less prone to congeal
on the plate. The darker the roux, the more