Baking bread is as much akin to alchemy as to science. The yeasts that give bread its rise are living creatures, and can be maddeningly sensitive to the smallest changes in temperature, humidity and ingredients. For example, if you're used to baking plain sandwich bread, you might find that making brioche or other rich, buttery breads can require some adjustments in your thinking. They often ferment rapidly, though it's not directly because of the butter.
Yeast Dough Basics
The character of any yeast bread is formed by a number of complex interactions. One is the growth of the yeasts, which feed on sugars found in the flour's starch molecules or other sweeteners added to the dough. They excrete alcohol and carbon dioxide gas. Proteins in wheat and some other flours form long strands, called gluten, when they're combined with water and kneaded. Gluten makes the dough stretchy and elastic, and as the yeasts produce carbon dioxide the dough traps it in thousands of balloon-like pockets. This is what gives bread its rise.
This process is referred to as fermentation, just as it is when the end result is beer or wine rather than bread. In beer-making the yeasts are manipulated to produce more alcohol, and carbon dioxide provides the foamy bubbles. In bread, alcohol production is kept to a minimum and carbon dioxide production is the goal. Small amounts of sugar in the dough encourage yeast growth, while salt slows its activity.
High Fat and Fermentation
Butter and other fats affect fermentation indirectly by coating the yeasts and other ingredients and making it harder for the yeast to feed. Butter or fats also slow and weaken gluten production by lubricating the protein strands and inhibiting their ability to link up into long chains of proteins. More beneficially, such fats soften the bread's crumb and make it easier to stretch and shape. They also give the bread a richer flavor and longer shelf life, which is why many festive breads and dessert breads have high quantities of butter.
Breads with high levels of fat often include relatively large amounts of sugar, for sweetness, and extra yeast to compensate for the way butter affects gluten development and reduces the bread's rise. The combination of extra yeast and extra sugar can have the unfortunate effect of causing a too-rapid rise. That leads to excessive alcohol production, which can leave the dough sour and coarse. There are several ways to adjust the recipe and minimize that risk. One is to slightly increase the salt, which slows the yeast's activity. Alternatively, you can reduce the sugar, the yeast, or both until you achieve a good balance of flavor and fermentation speed. A third option is to let the bread rise in a cool environment, such as a refrigerator, which slows the fermentation and limits alcohol production.
- On Food and Cooking: The Science and Lore of the Kitchen; Harold McGee
- The Bread Baker's Apprentice; Peter Reinhart
- Photo Credit Ryan McVay/Photodisc/Getty Images