Beer 101: Yeast

07-27-2016, The BeerVibe Crew

Yeasts in a fermenting tun, medieval, beer history, beer review, beer, beer review blog

For thousands of years the process that turned wort into the bubbling drink that was so enjoyable and in demand was known as either magic, miraculous, or just something that happened. If the brewster used the same brew stick to stir the pot, the miracle happened. If dust fell into the pot from the rafters, it happened. If she kept some of the stuff floating atop the current batch, she could add it to the next batch, and it would happen. She could also put it into her bread.

Yeast was on the barley grains. It was the whitish bloom that formed on dark grape skins. Yeast is in the air we breathe. It is practically everywhere, ready to fall into your mash. Also, bacteria could just as easily enter.

Sometime during the 1100s the aristocracy began taking over the brewing business from the monasteries and convents in Germany, and the quality of beer suffered accordingly. The aristocrats could issue and revoke licenses to brew, and come up with all kinds of cumbersome regulations; which may have impeded the development of better beers. However, it was noted in northern Germany where entrepreneurs in the brewing business were freer to experiment than their brethren in the south; that the temperature at which the wort fermented affected the outcome of the final product. It gradually dawned on some of them that beers brewed in colder temperatures were usually better and lasted longer than those brewed in warmer temperatures.

This all had to do with the yeast doing the fermenting. Two basic kinds of yeast found their way into the tun. Ale yeasts (saccharomyces cerevisiae) worked at warm temperatures (59⁰-77 ⁰ F) and formed a thick scum on the top. Lager yeasts (saccharomyces uvarum) worked at cold temperatures (39⁰-49⁰F), and worked beneath the surface and settled to the bottom; so they came to be called bottom fermenters. The bottom cold fermented beers were considered so superior to the ales that in 1553 Bavaria, in the southeast of Germany; prohibited summer brewing altogether. The legally permissible brewing season ran from September 29 through April 23.

From ancient times until science discovered how to control fermentation, both kinds of yeast floated in the air and fell into the wort. When it was warm, the ale yeasts did their work and the lagers stayed dormant. When it was cold, the lager yeasts worked and the ale yeasts slept. Either way, the brewer got some beer; usually of the ale variety if brewed in the summer and lagers if brewed in the winter. The froth floating on top and the sediment falling to the bottom of the tun were long considered the waste products of putrefaction. They didn’t know that the stuff they were discarding was actually the stuff that turned the wort into beer.

The regional summer brewing prohibition in Germany created a beer cultural divide, with the cold brewed lagers of Bavaria in the south and the old ale culture of the rest of Germany. With commercial interests in profits moving brewers to use the latest scientific discoveries to produce better, more competitive products. Well, that’s the subject for next time.


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