Lesson of the Day #6 - Curve Ball
While we learned that there are two types of beer, Ales & Lagers, and that they are differentiated by the kind of yeast used — top brewing or bottom brewing — there is actually a third, spontaneous or wild fermentation.
The original German Beer Purity Laws did not even include yeast as one of the ingredients, only water, hops & malt. Yeast was not considered a part of beer until Louis Pasteur discovered what it did during fermentation, caused by ambient yeast in the air, or from sediments from a previous batch being re-used by brewers.
It may seem risky today to let random microbes floating by be in charge of your brew, but some craft brewers still use (or have resurrected) the spontaneous fermentation process. However these wild yeasts and other microbes are cultivated and selected to create particular controlled flavors. Depending on the species, some of those flavors are described as 'barnyard' 'sour' and 'butterscotch'.
Trivia Question - What does the phrase rule of thumb have to do with beer?
Answer - Before thermometers were invented, brewers would dip a thumb or finger into the mix to find the right temperature for adding yeast. Too cold and the yeast wouldn't grow. Too hot and the yeast would die.