Dear Curious Baker,

The short answer to your question is yes: Fat really does interfere with the development of gluten by coating the proteins in flour that are responsible for forming gluten. Strong doughs usually contain very little or no fat.

Sometimes, however, in doughs such as brioche, the amount of fat included is surprisingly high. In this instance, the development of gluten is affected by when the fat is added while the dough is being made.

Some brioche recipes first make a simple dough with yeast, water, and flour. Softened butter is mixed in only after the dough has been formed and kneaded to develop the gluten. Once the gluten has been formed, it remains intact, and the butter has less effect on its strength.

Other brioche recipes add softened butter directly to the flour before the dough is formed. This method, of course, coats the gluten-forming proteins, so that once liquid is added very little gluten forms. Such a delicate dough (more like a batter) results in a very moist and tender brioche. It's quite different in texture from the more breadlike brioche.

As far as focaccia goes, it too is another variation on the gluten/fat story. Focaccia is traditionally a flatbread; it doesn't rise. Any oil or fat this dough contains helps inhibit the development of gluten in the dough, so the gluten doesn't develop too much as it's kneaded. Because the gluten relaxes when the dough rests, the dough has a slightly softer texture and is easier to roll or stretch to the desired flatness. The oil in the focaccia dough performs the same function as the butter does in the brioche.