Science of Cooking: Ask the Inquisitive Cooks!

" How does steaming baking bread help it be crispier? "

I am trying to learn why roux sauces get thicker when liquid is first introduced during cooking. Can you help me?

Bruce Moore, Florida

Still have more questions? You'll find more answers in our archived monthly feature articles by the Inquisitive Cooks.

( Meet the Inquisitive Cooks )

Dear Bruce,

Likely lots of people have wondered about this question, as indeed that's exactly what happens when liquid is first added to a fat and flour mixture. The purpose of the fat is to coat the flour particles, to keep them from clumping together so they swell independently as the liquid is gradually added.

When a sauce begins to thicken, the starches within each flour particle take up liquid. Initially, however, there is much less liquid in proportion to the number of thirsty starch grains. Thus, the mixture becomes very thick, very quickly. When the starch granules initially swell by absorbing liquid, you've basically made a thickened paste. Once they've been exposed to liquid and dampened, starch granules are primed to swell more as additional liquid is added.

As the proportion of liquid increases, the starch granules continue to absorb more liquid and swell in a process called "gelatinizing." This mixture becomes a sauce (or thickened liquid). Stirring is important to keep the starch granules, as well as starch that spills from ruptured granules, suspended and moving, which reduces the formation of lumps. Stirring also keeps the temperature of the sauce uniform so the sauce stays smooth as each starch granule takes up its share of water.

Though sauce-making is a basic task in cooking, the process by which they thicken is quite fascinating. Thanks for asking the question.

Wishing you many silky sauces!
Anne and Sue


- - - Science of Cooking - - - Webcasts - - - Ask The Inquisitive Cooks - - -