Selecting for yeast, Flocculation and Attenuation

Hey everyone.

So me and the head brewer of a local brewery were discussing the different properties of yeast banking/collecting/selecting

We were talking about how you would want to collect the trub from the primary and not the secondary (if you do secondary) because by collecting only the primary, you are selecting for more flocculant yeast with every collection. This is compared to secondary collection where you are selecting for yeast that are slower to drop.

Well, we were wondering if you choose continuously for the highest flocculating yeast, could you end up lowering your attenuation because the yeast will be dropping out faster?

This is making the assumption that the yeast that stay in suspension and in the krausen longer would continue to ferment longer compared to those that quickly drop out.

So basically, would selecting for more and more flocculant yeast potentially hurt attenuation? Just a thought were were tossing back and forth.

Also, the brewer is attempting open fermentation using a clean room. He wants to collect the yeast from these beers by skimming the krausen off and culturing the yeast from that. What are you thoughts?

Thank you for your time and I look forward to your thouhts.
Kyle

Well, how strongly you select for more flocculent yeast depends on how long you leave it in primary before harvesting. If you use short primaries, then you could potentially select for more flocculent yeast. But it would take many cycles before you would begin to notice a difference.
If the yeast was more flocculent, attenuation might suffer. But you could get around that by rousing the yeast frequently. I'm not sure how viable a plan that would be in a commercial brewery.

Top-cropping that way is a pretty common practice, at least in Europe. Not sure about the states. Some German breweries even do it with the thought that skimming of the kraeusen can help reduce off-flavors in the beer, though I'm not sure that's true. Maybe true of lagers, I doubt it's true of ales. It seem at any rate to be a good way to collect a consistent culture of yeast, but you need to be careful not to take enough to stall fermentation. So timing and quantity are important.