Brewer's Yeast Creates Love Nests in Wasps' Digestive Tracts

We have an unusual source to thank for the deliciousness of bread, beer, and wine: wasps. The yeast responsible for fermenting these goods, Saccharomyces cerevisiae, uses the intestines of wasps as a love nest, according to a new study in the journal PNAS on the reproductive habits of the species.

While most of the yeasts used in fermented foods and beverages are grown by inoculating a culture (in the case of wine, for instance, adding the yeast to crushed grapes), yeast also exists naturally in the air, in the soil, and on plants and fruit, such as the skins of grapes. However, how S. cerevisiae—commonly known as brewer's yeast—behaves in the wild isn’t well understood.

Yeasts can reproduce asexually, but they can also mate. To analyze the process of sexual reproduction in wild yeast, a team of European researchers fed different strains of S. cerevisiae yeast to a social wasp species called Polistes dominula. After the wasps hibernated for four months, the different strains of yeast mated with each other to form hybrids—an event that’s rare in domestic yeast, but can lead to new flavors of brew—and those strains survived at greater rates within the insects' intestines than in other environments.

“S. cerevisiae can outbreed within the insect intestine, and this seems to be the best currently known condition for this event to occur,” the researchers write.

After it moves through the wasp digestive system, the yeast is left behind by the insect—on grapes, for example. This is why wine fermentation begins when you break the skin of the fruit: The yeast on the outside finally has access to the sugary juice on the inside.

It's possible that yeast reproduces elsewhere—in other insects' digestive tracts, for instance—but the researchers will need to investigate other insect populations to know for sure. The discovery of a fertile breeding ground for yeast hints at how species of yeast might have evolved, and the importance of insects in that evolution. And because wine and beer makers are always on the lookout for new strains of yeast that might improve the flavors of their products, knowing that hybrid strains survive especially well in insect intestines could lead to new varieties of fermented beverages.