debeer1-4, Exercise 2: The cellars and the yeast

Model answer:

A Bavarian rule limited brewing to the cooler months, so brewers made beer in spring and stored it through the summer in cold cellars and caves, packed with ice cut from lakes in winter. The yeast that survived and kept working in those cold conditions was the cool-working, bottom-settling kind. Brewers reused yeast from batch to batch, so over generations they selected it without knowing what it was. The result was lager, shaped by the climate and the rules, not by any understanding of yeast.