It’s harder to imagine that a brewing strain would escape the brewery and go on to infect millions of Patagonian trees than to imagine it occurring in the reverse direction (or maybe I just don’t have much of an imagination). As far as your last question – with evolution, we can only observe what we have in front of us, whether is fossil bones or genetic evidence. We can’t say what strains may have existed before this one came to dominate lager production, but we do know that within a brewing environment there is a lot of selection for yeasts that perform well and a lot of competition for those that don’t. Even a small change in fitness combined with billions of generations of yeast propogation, would result in unfit strains going extinct. The 150-200 years thing is a back-of-the-envelope calculation. I don’t really know when the first true lagers were produced – we just know that people were brewing in cooler caves ~1400-1450 and that in 1553 Bavaria outlawed summertime beer production (presumably because they liked the low-temperature product better).

I’m completely serious about the old samples too – I’ve got a collaborator here who specializes in ancient DNA analysis (we’ve got a paper coming out in Nature next week that (I think) is going to get a shitload of press) and I’d love to be able to look at how lager brewing actually came into being (i.e. pre-European/American trade).

Second, I am completely out of my field of knowledge here, so I apologize if my questions are ignorant.

The incongruent time lines still worry me. How can we be sure about directionality? As I asked in an early thread:

Why isn’t that the missing link yeast went to S. America and found a safe haven while going extinct in Europe (can a yeast go extinct?)?

Similarly, can 150-200 years of lager brewing be easily replaced by the Patagonian yeast such that we have no other record of the preceding yeasts? Can we really account for current lager yeast strains to have come from one small place thousands of miles away, which traveled to Europe, then made its way into brewing, and finally imbedded itself so strongly that there is no sign of the previous cryotolerant yeasts?

I appreciate your feedback.