The vaults that keep old yeasts in ice

There are commercial labs that keep yeasts frozen in stasis - ready to be used in everything from bread to beer. BBC Future peers inside the freezer.

It's no secret that some of our favourite foods are the handiwork of microbes. Cheeses, breads, beers, yoghurts, pickles - maybe even truffles - all owe their distinctive characters to invisible bacteria, yeasts, and other fungi. Some foods rely on the critters that just happen to be in the vicinity - kimchi fermentation, for example.

But many involve microbes grown on an industrial scale by specialised companies. These bugs are the world's tiniest farm animals, in a sense - hundreds of thousands of tons of them are reared every year. To learn more about the process, I spoke to Karen Fortmann, a post-doctoral researcher who works at White Labs, a company that cultivates the brewer's favourite friend: yeast.

The first thing to know about these industrial cultures is that some of them are ancient. Companies store their stock in freezers, the microbial equivalent of cryogenic freezing. Fortmann says that some of White Labs' strains are much older than even the company, which has been around for 20 years. To produce yeast for clients to use, they thaw a thimbleful of the creatures and feed them on a malt-based solution, moving them into larger receptacles as they multiply.

White Labs grows primarily the yeast called Saccharomyces cerevisiae, the brewer's stalwart. They also grow S. pastorianis, a yeast used in lagers. But they do provide stranger varieties for homebrewers and other folks looking to experiment. "Now that people are starting to play around a little more," says Fortmann, "we have crazier types." One is Brettanomyces, a yeast long used in the making of lambic beers and Belgian ales that generates vinegar when fermented.

The company is cultivating some strains of bacteria, too, because beers made with them - sour beers - are growing in popularity.

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