Senne Valley lambic fermentation yeast spontaneous fermentation yeasts
Beers of spontaneous fermentation use wild yeasts rather than cultivated ones. By the Middle Ages, brewers had learned to crop the yeast from one brew and use it in the next. Only in a few isolated regions were wild yeasts still used. The best-known region where spontaneous fermentation is still used is the Senne Valley in Belgium where lambic is produced.
