" The key is gluten. Gluten is a protein with long, elastic molecules which simultaneously enable the dough to be made stronger (by providing structure) and lighter (by enabling the trapping of air bubbles). A lot of gluten means a firm structure, which is ideal for bread, but bad for pastry. Too little gluten means no structure and no air-trapping, so flat bread and tough pastry. The task of the pastry-cook is to get just the right amount of gluten to make the pastry light and crumbly and flaky. "

― Janet Clarkson, , Pie: A Global History