The Spring 2009 issue of Wise Traditions, a quarterly sent by the Weston A Price Foundation to its members, has an article by Katherine Czapp about traditional Scottish food. They too ate fermented food (pp. 56-7):
Farmers who grew their own oats but sent them to the local mill . . . received in return a bag of “sids” — the inner husks of the oats . . . From these sids, an ancient Celtic dish called “sowans” (or sowens) was made.
The sids were soaked in water for approximately one week (or even more) until they were well-soured.
Sowans takes more than week to make. Presumably the ancient Celts discovered this method of souring by accident and kept doing it because the result tasted good. It’s an example of how, in the right situation, what tastes good guides us to a good diet.