Just had a look at the all-time sale of my self-published books. And there was a slightly surprising winner. Especially as it was a relatively recent book
On the other hand, maybe not so surprising. As it is, basically, an add-on pack for The Homebrewer's Guide to Vintage Beer. My best-selling book by quite a long wa.
Which means there are a lot of people out there with the Vintage Beer book, but not the expansion pack. If you don't have it, I can highly recommend it: