I have read repeatedly that yeast will mutate after several reuses in the homebrew environment. If the yeast mutate at this high of a rate, how do breweries maintain consistent yeast characteristics, and how are pure cultures maintained without mutations?

Hi, long time lurker here. I am very interested in traditional brewing practices, and in researching the methods used in the past it is very hard to find information about yeast, primarily because brewers were unaware of its existence until recently. I would like a mixed strain yeast that I can reculture infinitely.