Milk

Fluid milk is, above all else, a source of water. In fact, it is primarily water—about 85–89 percent water. This means that any time milk is added to baked goods, water—which is necessary for gluten development—is also being added.

Fluid milk also contains glutathione, the reducing agent that softens dough. This becomes important in the production of yeast-raised baked goods, where the effects become noticeable during fermentation. If glutathione is not first destroyed, bread dough softens and becomes slack, and oven spring decreases. The result is lower loaf volume and coarser texture.