lection

the rise of yeast

3 april 2018

Ah, yeast, as Homer Simpson might say – is there anything you can't do? Yeast is even a prime ingredient in Homer's favorite doughnuts, though more beloved to the rest of the world for its contributions to bread, wine, and beer. In his global history of the little fungus, the groaningly titled Rise of Yeast, Nicholas Money certainly acknowledges food and drink. But the interplay between man and yeast (another of his puns) goes far beyond loaves and brewskis.

Yeast are simple, focussed organisms. They eat and they reproduce, on scales vast compared to their tiny, unicellular bodies: nuance is unknown to yeast. Yet they are surprisingly intricate. They are eukaryotes with cell nuclei, far more complex than bacteria. They are fungi, a status which lifts them, if not exactly above the plant kingdom, at least a step closer to the animals and therefore to us. And of course, they are one of the great species symbiotic to humans: for Money, perhaps the great symbiont, though of course he's writing a whole book about them and predisposed in their favor.

Most of Rise concerns Saccharomyces cerevisiae, "sugar fungus of beer": the workhorse of culinary fermentation, the one you buy in those little packets at the supermarket. Sugar fungus, Money suggests, hitched a ride with humanity somewhere in our deep prehistory. Reservoirs of sap and nectar, piles of decaying fruit, are among its native habitats. In the "drunken monkey" scenario of human development, people first noticed these natural happy hours and later learned to manipulate their production. Bread came well after beer and wine, probably the result of some accident that sloshed suds into matzoh dough. The rest is bubbly, if chametz, history.

But The Rise of Yeast is not entirely about making fermented foods and drinks. Money also covers the uses of yeast as an experimental organism, its status as star of gene-mapping labs, its role in manufacturing biofuels, and its impact on human health and illness. S. cerevisiae is only one of myriad yeast species. Though we make such pervasive use of it, the sugar fungus is oddly indifferent to us. Other yeasts live on our skin and in our guts, aiding our digestion and sometimes producing infections. (S. cerevisiae infection, an extremely rare ailment, can produce "auto-brewery" illness, where the yeast brew alcohol right inside your body and keep you slightly buzzed all the time – I gather not as pleasant as it might sound.)

Money briefly mentions the current fad of diagnosing intestinal Candida albicans buildup as an explanation for anything that ails ya'. Of course this is nonsense; C. albicans can cause infections of the mouth and vagina, but it is benign in the gut unless you're imminently fixing to die, in which case you have greater problems than mild indigestion and obscure lethargy.

The rise of C. albicans as a health-nut bad guy points, however, to the ubiquity of yeast. Yeast spores are so widespread that you cannot help but breathe them in every moment of your life; they may be literally responsible for rain, as the dominant nuclei of precipitation. Among the vividest takeaways from The Rise of Yeast is the sense of how embedded we huge creatures are in a microscopic biota.

Money, Nicholas P. The Rise of Yeast: How the sugar fungus shaped civilization. New York: Oxford University Press, 2018. QR 151 .M73

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