The below pretzel recipe calls for either dipping your pretzels in a lye bath or simply painting them with egg wash. However there is another method that’s very commonly used. It involves poaching your pretzels in boiling water to which a large volume of baking soda has been added. Soda, as you most of you folks already know, is an alkaline. It’s nowhere near as strong an alkaline as lye, but it will produce a similar, if not nearly as pronounced, effect. The ratio of soda to water required is about half an ounce per 8-ounce cup of water.
But then if you don’t have to use boiling water with lye, why must you use it with baking soda? Part of the answer is that the hot water helps the soda dissolve. However the poaching also causes the starch on the outside of the pretzel to gelate, which is to say it causes individual starch molecules to separate from their flour granules and form an interlocking network. This helps hold in the rise of the pretzel in like a girdle, thus maintaining a tight, chewy crumb. This is one of ways in which pretzels resemble bagels.
Why don’t you need the girdle effect when you use lye? Simply because the carbonate crust that the lye reaction creates does the job handsomely. It’s like a baked-on enamel coating that constrains the rise beautifully all by itself.