Traditional pretzels are typically submersed in an alkali "bath" before baking, which produces the glossy browned smooth surface on pretzels. Home bakers often opt for baking soda and water as an alkali bath, which is what we use in this recipe. Commercial bakers and some die-hard pretzel fans use lye, a caustic alkali that can be dangerous if used incorrectly. I prefer to error on the side of caution and stick with baking soda. This article on the King Arthur Baking Company website offers tips on making homemade pretzels with and without lye.