Structure & Butter

Reader Robert writes:

I have a sciencey question for you regarding mixing in the butter for brioche. All the recipes I have seen say to mix the butter in after the dough is formed. I am wondering why.

By my reasoning, mixing the butter into the eggs before adding the flour would seem to be a whole lot less messy, and the emulsifiers in the eggs would help to keep the butter in place. I’ve not really had an opportunity to try this out, but I’m wondering if you know of some reason why this wouldn’t work?

Excellent question, and one that’s very pertinent to the current project, since gâteau battu is so similar to brioche. It employs many of the same methods…including the working-in of butter once the basic dough is formed.

There’s very good reason to do this, and it all has to do with gluten development. Brioche as you know is a very rich dough, it contains plenty of egg yolks and butter. To lift all that the brioche needs a highly developed structure, which is to say a network of gluten molecules that will capture and hold steam so the brioche can rise.

Gluten formation takes two primary things: moisture and beating/kneading. The wetness and agitation encourage the gluten molecules to come into contact and bond to one another. However gluten molecules can’t bond to one another if other kinds of molecules are in the way, i.e. if they’re coated with fat. So when making something that rich but that also needs a sturdy structure — like brioche — we develop the gluten first, then work in the butter. Once those molecules have hooked up, no amount of fat is going to unhook them.

Make sense? Thanks for the great question, Robert!