Bread doughs that contain substantial amounts of fat and/or sugar pose special challenges to the baker. Both fat and sugar slow gluten development and weaken it, sugar because it binds up water molecules and interrupts the gluten-water network, fat because it bonds to fat-loving portions of the gluten chains and prevents them from bonding to each other. Rich doughs are therefore relatively soft and fragile. Bakers often build them by holding back the fat and sugar and kneading these in only after developing the gluten network, and then bake the doughs in containers that support their weight and prevent them from sagging and flattening. Large amounts of sugar slow the growth of yeast by dehydrating the cells, so sweet doughs are often made with more yeast than ordinary breads, and they may take longer to rise. Sugar also makes sweet doughs prone to begin browning early in the baking, so they’re usually baked at a relatively low oven temperature to prevent the surface from browning before the interior has set.