Since antiquity, civilizations the world over have reveled in the ability to make alcohol, praising their gods for sending them the heavenly nectar that makes a man brave and his companions attractive. However, it wasn’t until some years after Antoni van Leeuwenhoek discovered his animalcules that people began to suspect that it is neither Aegir nor Mayahuel they have to thank for their mead and octli, but a microbe: Saccharomyces, or, as it’s more commonly known, yeast.
For millennia, people have taken advantage of the byproducts of a process called “fermentation.” The word fermentation has its origins in the Latin word fervere, “to boil,” as a result of the observation that bubbles form in fermenting substances, as if they were boiling. Alcoholic fermentation is one of several forms of a metabolic process called “anaerobic respiration.”
In cellular biology, respiration is the process by which nutrients, including sugars, are converted into molecules that are useful sources of energy for a cell. Anaerobic respiration is respiration that occurs when oxygen is absent.
While human cells also carry out anaerobic respiration, it is a different process than yeast’s alcoholic fermentation. In a massive blow to efforts to improve cardiovascular health, it turns out this form of fermentation, “lactic acid fermentation,” ends with the production of lactate by muscle cells, not alcohol. Thus, rather than getting progressively drunker during exercise, a person is left utterly sober and with a burning sensation in their muscles.
The hijacking of alcoholic fermentation by unwitting humans began as early as 7,000 years ago, likely accidentally. A careless farmer sealed an improperly cleaned jar containing fruit or grains, and resident microbes were happy to snack on what had been stored inside. When the jar was opened, the unsuspecting consumers would have been pleasantly surprised to find a fizzy, liquid mess that made their heads buzz.
These happy accidents have since been refined to an art form. Even before we had any awareness of microbes’ existence, much less of the critical role they play in fermentation, early brewers, vintners, and distillers discovered how to create an ideal environment for alcohol production through extensive trial and error.
In addition to aiding in the release of sugars, heating the sugar sources and water to high temperatures before fermentation kills microbes that could compete with yeast. This microbial competition could digest the sugars into compounds that, at best, affect the alcohol’s flavor and at worst are toxic. Ideal fermentation temperatures were found for the yeast to happily produce large amounts of “good” alcohol, without gorging themselves and producing off-flavors. Even the tradition of crushing grapes for wine by stomping on them may have helped along the fermentation process by transferring microbes, including yeast, from bare feet onto the crushed fruit.
The most commonly used brewer’s, distiller’s, and vintner’s yeasts are strains of Saccharomyces cerevisiae, the same species of yeast used as a leavening agent for bread. Different strains of S. cerevisiae have been cultivated for characteristics that make them suitable for different uses. Baker’s yeast carbonates dough very quickly and produces very little alcohol, making it ideal for producing light and fluffy dough, while brewer’s yeast is less aggressive, carbonating at a slower rate and allowing for the production of greater amounts of alcohol.
By the mid-eighteenth century, it was clear that the substance that was then simply called “ferment” was required to make both bread and alcoholic drinks. However, it wasn’t yet known that this substance was a living organism. Several of the most important minds in the foundation of modern science carried out the quest to discover how fermentation took place, which led to several key discoveries in the early days of biochemistry.
Antoine Lavoisier, a chemist widely regarded as the “father of modern chemistry,” first confirmed that yeast was fermenting our alcohol. He showed that 1/3 of the sugar added to a fermentation reaction is oxidized into carbon dioxide, hence the bubbles found in fermenting liquids, while the final 2/3 is reduced to alcohol. Lavoisier further found that “ferment” was absolutely necessary to catalyze this reaction, and that it remained unchanged from start to finish.
From the microbe’s point of view, the alcohol and carbon dioxide produced during fermentation are actually harmful waste products to be discarded. As more alcohol is produced, it eventually reaches levels that are toxic to the yeast. This is why beer and wine have on average 5% and 12% alcohol contents, respectively; any higher and the yeast begins to die (spirits begin their lives with similar alcohol contents, but are distilled down to higher concentrations.)
In 1835, Charles Cagniard de la Tour took Lavoisier’s work a bit further by showing that yeast multiplies during fermentation through a process he called gemmation. This process, also called “budding,” is a form of asexual reproduction in which a cell splits itself into two exact copies of itself.
Just over twenty years later, famed microbiologist Louis Pasteur showed that not only does yeast multiply during fermentation, but also that this multiplication and the production of alcohol occur in parallel. Additionally, he showed that the yeast had to be alive for this process to occur; if he boiled the yeast before adding it, fermentation never began.
Though these observations seem obvious to those with a modern understanding of microbiology, it was an important discovery at the time. These facts combined indicated that fermentation is a direct result of yeast replication and growth. Pasteur thus showed for the first time that not only is fermentation a process that is carried out by a microorganism, but that it is one that is required for that microorganism to live and thrive.
Pasteur went on to fully develop our current understanding of fermentation, elucidating in detail the step-by-step process of fermentation. He also was the one to coin the phrase “anaerobic respiration” after having established that fermentation only occurs in the absence of oxygen.
Though years of study have taught us that alcohol wasn’t bestowed upon us by the great god Bibulous, we should still remember that it is a gift. The next time you meet your friends out for a drink, raise your glass to Saccharomyces cerevisiae, the microbial benefactor of booze lovers everywhere.