Roux

Roux is best made fresh for immediate use. If made ahead, it can be refrigerated for a day or two, but its thickening power may diminish.

Cook the roux until it reaches the desired color, from pale white for béchamel to deep brown for gumbos, to develop flavor.

Always whisk the roux into a liquid (or the liquid into the roux) gradually and whisk constantly to prevent lumps.

Simmer the sauce for at least 5-10 minutes after adding the roux to cook out the raw flour taste and allow it to thicken fully.

Béchamel sauce

Velouté sauce

Espagnole sauce

Gumbo

Gravy

Cream soups

Adding cold liquid to hot roux, or vice versa, which can cause clumping.

Not cooking the roux long enough, resulting in a raw flour taste.

Burning the roux, which will impart a bitter flavor to your dish.