The Blessings of Yeast, “Mother of Fermentation”*

■ Function and Domestication of Yeasts for Fermented Foods

Do you know about yeast? Its Japanese name, kobo, means “mother of fermentation,” lending it a kind of benevolent impression, creating a delicious sort of ambience. What kind of “person” is yeast, however? Where did she come from? There might be only a few people who know these and other facts about her.

“Yeast” is the generic term for the Eumycetes (true fungi), which grow as single cells for certain periods in their life cycles. In simple terms, they are categorized roughly as “eukaryotes that live as single cells.” Therefore, yeasts include “true friends,” but of course also “villains.” For example, the fungi living on your father’s feet giving him cutaneous candidiasis, are also a kind of yeast, as are those that cause cryptococcosis. In other words, we humans are making adept use of the “true friends” among yeasts in fermentation, but they comprise only a small subcategory of yeasts.

■ The Functions of Yeasts in Fermented Foods…

We humans make use of various different kinds of yeast in fermented foods. While in the production of miso and soy sauce, Zygosaccharomyces rouxii and other species are used, the role of Saccharomyces cerevisiae that we use not only for brewing Japanese saké, beer, wine, and other liquors, but also for fermentation in bread is so significant that like Shohei Otani of baseball fame, it would win the yeast world’s Most Valuable Player Award if there were one. So, what role does Saccharomyces cerevisiae play in fermentation processes?

Saccharomyces cerevisiae carries out alcohol fermentation in anaerobic conditions devoid of oxygen, producing ethanol and carbon dioxide from sugars in the process. In the case of liquor, it is the ethanol that is used, while in the fermentation of bread, it is the carbon dioxide that is used. Yeasts also produce various aromatic components and organic acids. These add characteristic flavors to each of the various fermented foods it is used in. If we were just to add ethanol and carbon dioxide to these foods, it would not produce the same delicious flavors that fermented foods have. In other words, fermented foods become possible only if the harmony of the various fermented components that these microorganisms so skillfully create is present.

■ The Evolution and Domestication of Yeasts

So then, where did Saccharomyces cerevisiae originally come from? The fact is, yeasts are living everywhere throughout the natural world, like feral children, each with its own personality. There was no way for our ancestors to know that yeasts existed; they took fermented foods to be a “blessing from the gods.” They sought to identify the conditions under which delicious fermented foods could be produced, asking if the gods (actually, the yeast) were happy with this or that, developing only the brewing or fermenting techniques that would encourage the gods (yeast) to manifest. They also selected the most delicious products from among fermented foods, and by obtaining natural variants of yeast with properties more suitable for food fermentation, they developed them into yeasts with superior fermenting capabilities. That is to say that during our long history, we humans domesticated yeasts in our pursuit of more highly delectable fermented foods.

* The English title has slightly been changed from the panel.