Pretzels are unusual for their woven shape, dark brown crust, and unusual flavor. Like crackers, they’re made from a stiff yeast dough of soft wheat flour. In manufacturing, the formed dough is sprayed for 10–15 seconds with a hot 1% solution of alkaline sodium hydroxide (lye) or sodium carbonate. The heat and moisture combine to gelate the surface starch. The dough is then salted and baked for about five minutes in a very hot oven. The starch gel hardens to a shiny finish and thanks to the alkaline conditions created by the lye, browning-reaction pigments and flavor compounds rapidly accumulate. (The lye reacts with carbon dioxide in the oven to form a harmless edible carbonate.) The final step is a long, slow bake to dry the whole pretzel out. The pretzel is crisp but fragile thanks to tiny airy bubbles and ungelated starch granules throughout, and it has a distinctive flavor from its alkaline-browned surface.