Making a lump-free roux
A roux is flour cooked in fat, usually in equal weights. The fat coats the flour grains, so when liquid arrives they spread out instead of clumping. Then heat swells the starch and thickens the sauce.
Cook out the raw taste
Flour straight from the bag tastes pasty. Stir a white roux 1 to 2 minutes over medium heat, until it smells slightly nutty. Blond takes about 5 minutes. A dark gumbo roux takes 20 to 45 minutes of nonstop stirring.
Darker roux means less thickening
Cook a roux longer and it builds a nutty, toasty flavor, but the starch breaks down. A dark roux thickens much less than a pale one, so gumbo uses more roux or less liquid to make up for it.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Flour stirred straight into hot milk forms lumps, but the same flour made into a roux doesn't. Why?
Fat coats and separates the flour grains. Separated grains get wet evenly instead of clumping.
True or false: A darker roux thickens better than a pale one.
False. Longer cooking breaks down starch, so a dark roux thickens much less than a pale one.
What went wrong? You dump cold milk into a hot roux in one go and stir. The sauce is full of lumps.
All the liquid hit at once, so the flour clumped. Adding it a little at a time while whisking lets the flour spread out evenly.
Fill the blank: Add the first splash of liquid and whisk until the roux becomes a thick ___ before adding more.
Add the first splash of liquid and whisk until the roux becomes a thick paste before adding more. A smooth paste means every grain is wet, and then you can thin it step by step.
True or false: Cooking flour in fat is pointless, since you could just stir flour straight into hot liquid.
False. Raw flour in hot liquid clumps into lumps with dry centers and tastes pasty, and a roux avoids both.