ELI5: Why can’t other yeasts be dried like kveik?

[Steven Barrett]

Request for someone to explain why other yeasts can’t be dried in the oven/dehydrator at home like kveik can. What I’ve read is kveik is used to it and other yeasts aren’t. Can anyone elaborate on why?

 

[Stollejocke]

Kveik has been used like that for hundreds of years in norway. So i guess the yeast just adapted

 

[Northern_Brewer]

It's more the other way. One reason yeasts are so successful in the wild is because they can survive in dry form over the summer on fruit trees, vines etc and then revive when the rains come. It involves a lot of different factors, mostly to do with membrane structure but also heat-shock proteins and others - yeast that like extremes of hot and cold seem to be better at surviving desiccation in part because they have more sophisticated control of their membranes to cope with temperature swings.

But this comes at a biological "cost", so the ability to survive desiccation may be lost if it's not needed. A British yeast that's had a soft life being repitched in a brewery has not experienced desiccation for centuries, so it's no wonder that they don't cope well with it - you can regard a lack of desiccation tolerance as a sign of domestication. Whereas kveik was regularly exposed to drying so it didn't lose the ability to survive it, it failed to "unadapt".

If you want to get more into the science of all this, search your favourite academic source for yeast anhydrobiosis.

 

[Steven Barrett]

@Northern_Brewer thanks for the explanation. I’ve also wondered how long it takes yeast to evolve. Like for example, could a homebrewer keep top cropping and repitching yeast enough times for it to evolve to express different characteristics? Are there any sciency articles on that?

 

[Northern_Brewer]

Depends what you mean by "evolve" - in one sense you have "evolved" compared to your parents. But in general it depends on the pool of variation and the selection pressure, so for instance you can expect flocculation characteristics to "evolve" pretty quickly as there seems to be quite a variation in flocculation among the typical yeast population, and it's easy for humans to exert extreme selection pressure on it. So when British breweries switched from top-cropping open fermenters to conicals where they bottom-cropped, they found that their yeast pretty much switched from top-fermenting to bottom-fermenting overnight.

Flavour is more complicated, as it tends to involve gene pathways so there tends to be less variation at the phenotype level to work on, and unless you're picking out single CFUs to trial then you don't get the same selection pressure (unless it's something really obvious like phenol production). And some strains are more subject to variation than others - Pinot Noir is notorious for it in the grape world. But anecdotally, in commercial breweries that are repitching yeast every week they get something that's regarded as a different strain within 10-20 years or so.

There's a lot of working going on at the moment in this field, as the ability to sequence genomes cheaply has transformed our ability to trace these kinds of genetic changes over generations. It's early days yet so not much has been published, @suregork will be more aware than me of what's bubbling under the surface.