Reader T wants to know why the mooncake crust recipe below calls for baking soda AND Chinese lye water. It’s an excellent question and I believe the answer is twofold. First, an extremely alkaline dough will brown up more readily. I mentioned Maillard reactions in a post a few days ago. One aspect of these mysterious browning reactions that I failed to mention is that they happen faster in an alkaline environment. It’s one of the reasons breads like pretzels and bagels are dipped in a lye solution before they’re baked. Chinese mooncakes don’t spend much time in the oven, so to get even a mildly browned appearance the pH needs to be fairly high. I don’t know what the pH of Chinese lye water is, but it’s must be higher than that of baking soda (9). Otherwise, why use it?
The other reason an alkaline dough is advantageous here is because alkalinity undercuts gluten development. That’s a good thing in this instance since as I mentioned earlier any significant rising will “erase” the delicate patterns on the top of the cakes as they heat up.