Yeast is a vital ingredient in breadmaking, providing lift and lightness and giving the bread a doughy flavor. The Saccharomyces cerevisiae species is especially suited for modern bread processing because it is food-grade and relatively low-cost.

The yeast breaks down the carbohydrates in the flour and releases carbon dioxide, which remains trapped in the dough and expands it. Producing breads involve two stages of proving: the first one is after the dough is divided and then after it is molded.

In the oven, the dough continues to expand while losing weight. A moderate heat transforms carbon dioxide in solution into a gas, occupying the microscopic cells. But as ethanol caused by fermentation evaporates, the mass becomes lighter.

The crumbs, however, need a higher temperature (around 60°C) to start stabilizing into a paste. The last yeast cells are killed when the heat reaches 74°C, but the loaf is not fully cooked until the crust forms at 160°C. The browning occurs as sugars contained in the flour caramelize.