This step determines the character of your roux. In any case, the mixture should not smell of raw flour. (Take a whiff of a bag of flour if you aren't sure what raw flour smells like.) Keep the mixture moving so it doesn't burn.

• White roux: barely beige; complete in no less than five minutes.
  Blond roux: golden; usually complete in 10 minutes.
  Brown roux: deep nut-brown; this roux is often cooked from 45 minutes to 1 hour and smells nutty and baked when it's done. Most chefs use clarified butter (see Keywords) when preparing a brown roux.