Yeast: It Eats Sugars And Poops Alcohol. Whats Not To Like?

THERE ARE MILLIONS OF TINY THIEVES waiting to steal our food. Take a bite out of an apple and you’ll see them go to work in a matter of minutes: tiny airborne microorganisms will settle on your fruit and start chewing away. There is mold, for example. An estimated 100,000 species of this single-celled fungus float around us, unseen, looking for something moist and nutritious to settle on and start devouring. Sometimes they’re just looking to muscle in on your apple â€" the mucor mold, for example, travels in house dust and will quickly cover the surface of your fruit with a cotton-candy like growth. Some of these microorganisms are actually looking to feast on us, such as the fungus Candida albicans, which causes yeast infections.

Much of human history has found us at war against these microbiological thieves, trying to preserve our food supply from the spoilage they inevitably produce. We have dried our food, salted it, bottled it in brine, frozen and refrigerated it, treated it with potent chemicals, all in order to discourage yeast and molds from eating our meals before we get to them.

And yet, in this million-year, multi-billion dollar war against airborne fungi, we have made some unusual alliances. We’ve developed a great friendship with yeast, as an example; at least, with yeasts other than Candida albicans. We toss Saccharomyces cerevisiae yeast on grains, add sugar and water, and let the fungus chew away. It excretes carbon dioxide, which gets caught in the dough as tiny bubbles, causing it to expand. Toss the resulting leavened dough into an oven and, voila: bread. We don’t often think about it when chewing on a baguette, but our meal of French bread wouldn’t be possible without the gas that yeast passes. Without the useful flatulence of Saccharomyces cerevisiae, we wouldn’t have bread, but for matzah.

Just as we have learned to enjoy the gaseous emissions of certain yeasts, we have also learned to use their other waste products. In fact, we wouldn’t be able to enjoy a cocktail without them, because alcohol is, fundamentally, yeast poop. We don’t know precisely when humankind discovered the pleasures of this waste byproduct -- certainly the discovery dates far back in prehistory. After all, berries and grains left on their own often turn alcoholic with no help from anybody. It is easy to imagine starving troglodytes innocently swallowing these high-proof berries and grains, unaware of the intoxication -- and hangover -- to follow. We do know that the brewing of alcoholic beverages occurred early on in the history of agriculture; some anthropologists argue that early humans actually abandoned their hunting-gathering ways in favor of an agricultural lifestyle in order to maintain a constant supply of hootch.

It couldn’t have taken too long to discover that yeast was the culprit in the creation of alcohol, although precisely how the yeast worked wasn’t divined until 1856, when a student of chemist Louis Pasteur asked him to look into the fermentation of beetroot, which often produced lactic acid instead of alcohol. At that time, it was widely believed that sugar spontaneously turned into alcohol through an exclusively chemical process. By watching fermentation under a microscope, Pasteur determined that it was yeast that produced alcohol, and that microorganisms in the air could sour the fermentation process. Pasteur discovered that heating alcoholic products -- as well as milk and vinegar -- would kill unwanted organisms. This process is still used nowadays, and is named after the scientist -- it’s called pasteurization. Pasteur would later use this research in developing his theory that germs caused disease; the treatments that arose from his theory have saved untold millions.

It’s not surprising that Pasteur became obsessed with health problems created by microorganisms. After all, he had discovered that alcohol, the beverage that might have created human civilization, was essentially the toilet water of a fungus.