I have already said everything, if you think you know better, your choice.
They are saying that you have dead + alive in both the sediment and in suspension. Since you cannot mechanically separate (filter) dead yeast from live there are no good ways to achieve this without a viability stain, manually isolating a few active cells into a very small starter, and step it up from there.
Actually, I was trying to stop you from misdirecting into semantics. Yeast are not capable of motility in the biologic sense of the word, so using that term in this thread is a distraction. We got hung up on that once already and I don't see any point in doing so again. As for the topic at hand, maybe, you could try reading everything that was posted since the last time you were here.
CO2 can only carry the yeast upward if it's bubbling up from the bottom of the vessel. Which everyone who's ever used a clear fermenter knows it is. Yeast are everywhere in the liquid during active fermentation.
It's mainly the escaping co2 which forms bubbles which induce currents. Additionally, if the yeast flocculates during that time, these flocs can trap co2 which transports the yeast to the surface where it might form a barm or Kräusen. It's a co2 yeast foam.
The live cells would only create "propulsion" if CO2 was released directionally. It isn't. CO2 release churns up the ferment. So does heat release. And gravity is acting relentlessly at the same time. Everything in the vessel will get moved around to a greater or lesser degree. Denser stuff will rise more slowly and sink more rapidly. That's really the only differentiator as far as I can see.
The CO2 gets out of solution, not out of the yeast cells itself
CO2 is a byproduct of fermentation. I take this as the CO2 is created by the yeast when they consume sugars. If the CO2 is created by the yeast, it would be coming from them, not the wort. Are you saying CO2 is already latent in the wort and it is being released by yeast heat and activity?
Let's assume that CO2 release provides "thrust". Why should we think that this thrust is always upward as opposed to random? So maybe some of the live yeast cells would get propelled upward, but wouldn't many others get pushed downward or sideways?
Convection currents and CO2. Forget about whether yeast are capable of locomotion for a minute and ask yourself why they would want to move around in the first place. The stuff they want to eat is everywhere in the wort.
CO2 actually does come out of the yeast cells themselves. It's generated inside the cells and they have to get rid of it. Same as the ethanol and all the other byproducts of their metabolism.
Good points.
It is released by the yeast into the wort. But not through bubbles. It is in solution when it's going into the wort. The bubbles are forming in the wort when equilibrium of solubilitie is reached.
I recall seeing, hundreds of years ago, a phenomenon called "bees wine". A highly clumping yeast would be inoculated into a sugary solution and the clumps would rise slowly from the bottom to the top and then slowly sink again. The object was to offer something fsscinating to interested kids, not to produce a decent drink.
Around any solid mass, some nucleoid points are formed at which co2 falls out of solution and builds bubbles. It doesn't differentiate between dead and alive, it just needs small points to attach to which almost every non-liquid medium will deliver.
While I agree with what you say, doesn't that presuppose the liquid already has some of the gas dissolved in it, possibly at a level approaching saturation? I'm talking about a recently-boiled and cooled wort that would have a minimum of dissolved gases and so the only gas attaching to the cells would be that secreted by the live cells themselves, which would then begin to float. Of course there is no reason why proximate cells shouldn't be carried up as well, but I think we' might see a decrease in the overall number of dead cells in the liquid part of the system after the slurry has settled to the bottom. I suspect all this could be kicked into the long grass by Brownian motion more than nucleation of new bubbles. The question is whether it would work well enough to make a significant difference. What do you think?
It doesn't work like that. First, there is co2 already in solution. Second, as soon as yeast starts to produce and excrete co2, it spreads evenly. So if bubbles are forming, they're forming everywhere they can at nearly the same time, dead or alive material included. Then, when they start to rise, everything gets mixed anyway.
Just start with a small amount of the yeast cake and step it up. Plating runs the risk of isolating and propagating a mutant. Unless you have a way to rapidly screen colonies for the desired genotype or phenotype. Talk about something that most homebrewers don't have the wherewithal to do.
I think we've all had a few of those. My day and his paisans all used to say that their wine was "still boiling" during active fermentation. It's a pretty apt description.
Sorry to disagree, I think we may be talking at cross purposes. Freshly boiled and cooled wort didn't contain CO2 in solution until the yeast puts it there. As soon as the yeast starts producing it doesn't immediately go into solution, the nascent CO2 attaches to the yeast and causes it to float. So there may be a window of opportunity to collect relatively "clean" yeast. Your final point may, indeed, negate this as the rising yeast may bring up sufficient dead yeast to make the opporation futile. Or not. That is the question.
Yeah, pretty sure you are. Do yeast excrete dissolved CO2 or "burp" out gas? I seem to recall seeing a paper that showed gas bubbles in active yeast cells, but I can't find it now.
The co2 literally is in solution while being produced as all the metabolism is happening in solution.
Not to stir the pot, but there was an interesting paper on this a while back, in which the authors observed CO2 bubbles in yeast, and posited that they may be directly excreted. Completely backwards from intuition (mine, anyway)!
