The Rising Power of Yeast

In the last chapter, yeast was mentioned a few times as one of the generally less-problematic microbial denizens of food systems, and in fact the roles of yeast in the production of two of our most common and popular food categories, alcoholic beverages and bakery products such as bread, are so critical that it is worth dedicating a whole chapter just to the consideration of the science of these products. The ability of yeast to grow in a wide range of raw materials and convert sugars to alcohol, carbon dioxide, and other interesting products is the basis for production of products such as wine and beer, as well as higher-alcohol-level spirits, and is a process that has been exploited for the purposes of human pleasure for thousands of years. The origins of alcoholic fermentations, like those of many food products, are somewhat murky, but it is thought that honey or fruit may have been the original basis for the fermentation of such products, and that wine arose because of accidental adventitious spoilage of grapes and their juice that turned out to have, well, interesting consequences. The Greeks and Romans had wine-making down to an art, and it features frequently in their art; it also makes many appearances in the Bible (including a nonscientifically verifiable production protocol based apparently solely on water). The main reason alcoholic fermentation became of interest was as a way to prevent bacteria or other undesirable microorganisms from growing in juice by allowing a different kind of microorganism to get there first, use up the goodies, and produce products that made conditions highly unsuitable for colonization by later invaders. We routinely associate the word “intoxicated” with a formal description of the result of overconsumption of the outputs of such fermentation, but the heart of that word is “toxic,” which reminds us that alcohol is a poison. It just happens to be one that humans can tolerate only up to certain levels, beyond which poisoning and death can readily occur, but at lower levels has a range of effects that need not be described here.