When fermenting beer, we homebrewers are cautioned to culture fresh yeast every ten generations or so (ale). The basis of this assumption is that after ten or so generations, the yeast will have mutated away from the initial strain as they adapt to the conditions in our brewery. But then, there are tales of breweries that never change their yeast, they just keep pitching the same yeast one batch after the other for decades, if not centuries. I recently read an article in Quanta Magazine that may explain those breweries’ success: convergent evolution.
The thought is, or was, that evolution was divergent, that a small change could drastically affect the outcome of evolution. The researcher, Michael Desai, created hundreds of identical worlds for yeast cells to live in then pitched identical yeast cultures into each. After five hundred or so generations of taking the fittest cells and repitching them, it turns out each group had very nearly the same characteristics. It’s as if each arrived at the same place by taking a different path. And it could explain why some breweries have been using the same yeast for so long successfully: Every set of mutations in the nearly identical conditions of the breweries’ fermentations converged on the same place.
I don’t know how to test this in a brewery environment but wouldn’t it be fascinating if our yeasts, too, were convergent? We generally don’t brew the same beers every time and don’t create identical environments but a commercial brewery might. If the various mutations of yeast in these worts, still random, led to the same place, it would explain why centuries-old cultures still make good beer. The brewer has set up conditions favoring that culture and the mutations that inevitably arise in their yeasts would lead back to the same place.
Convergent evolution could be our friend. If I hear more, I’ll let you know.