In the first decade of the 1800s, French chemist J. L. Gay-Lussac took one step closer to understanding yeast. Gay-Lussac filled flasks with grape juice and placed them on ring stands. Beneath each one he lit a Bunsen burner and boiled the liquid until the aroma of Chardonnay permeated his lab. As soon as he turned off the flame, he stoppered each flask and let the liquor sit for a year. He was aware, as all good Frenchmen were, that unboiled grape juice left for a year became wine, or at least vinegar.
Only once he opened his flasks and exposed them to air did his grape juices begin to acquire the aromatic and chemical characteristics of fermentation. His conclusion, dead wrong, was that heat from his Bunsen burner had deactivated his globules and that inrushing air contained the chemicals necessary for fermentation. In truth, once his flasks were unstoppered, bacteria and yeast charged in, landed happily in his sterilized liquids, and began at once to consume grape sugars.
Another piece of the puzzle was placed in August 1819, when so-called blood burst from a batch of polenta in Padua, Italy. The peasant who had cooked it tossed the batch, but the next day it reappeared in his bowl of fresh polenta. A priest was called to pray over the peasant’s polenta, to no avail. The following day, the epidemic of bloodstained polenta spread to other households. The press went wild. Soon everyone knew of the terrifying signals appearing in Padua.