Tips on separating dead yeast from fresh ?

[Miraculix]

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?

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.

 

[An Ankoù]

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.

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.
I had always thought that the gas which the "clump" exuded remained associated with the clump, being held there by the "skin" of surface tension of the liquid at the interface of the bubble rather than going immediately into solution, When the clump reached the top of the liquid, some of the bubble was discharged into the atmosphere making the clump heavy enough to sink again.
Does this offer any insight into what might be going on in a vessel full of fermenting beer?

I have had beers (few and far between, thank Odin) where the vessel appears to be literally boiling- like the hard boil of a kettle. Touching the vessel indicated that, while it might be a bit warmer than ambient, it is by no means hot so the "churning" can't be fully explained by convection currents.

Edit:
Thinking aloud:

This would have implications for separating the quick "from the dead" using a fermentable medium provided the live-yeast-charged liquid were decanted off the rest of the dregs before the internal action became sufficiently violent to put the whole mass in motion. But it wouldn't help with the idea of simply rinsing the yeast in plain water.
That's all presuming I'm right with my "bubble" theory of course.

 

[Miraculix]

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.
I had always thought that the gas which the "clump" exuded remained associated with the clump, being held there by the "skin" of surface tension of the liquid at the interface of the bubble rather than going immediately into solution, When the clump reached the top of the liquid, some of the bubble was discharged into the atmosphere making the clump heavy enough to sink again.
Does this offer any insight into what might be going on in a vessel full of fermenting beer?

I have had beers (few and far between, thank Odin) where the vessel appears to be literally boiling- like the hard boil of a kettle. Touching the vessel indicated that, while it might be a bit warmer than ambient, it is by no means hot so the "churning" can't be fully explained by convection currents.

Edit:
Thinking aloud:

This would have implications for separating the quick "from the dead" using a fermentable medium provided the live-yeast-charged liquid were decanted off the rest of the dregs before the internal action became sufficiently violent to put the whole mass in motion. But it wouldn't help with the idea of simply rinsing the yeast in plain water.
That's all presuming I'm right with my "bubble" theory of course.

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.

 

[An Ankoù]

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?

Probably better to just plate up a sample and build up from there, but not everybody has the wherewithal to do that.

 

[Miraculix]

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?

Probably better to just plate up a sample and build up from there, but not everybody has the wherewithal to do that.

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.

I think many people are heavily overthinking this topic.

 

[mashdar]

How to separate dead yeast: Don't?

1. Dead yeast is food for live yeast. In fact, it's common to boil and add baker's yeast for YAN in cider/mead/wine making.

2. The culture is weak. The more you handle it, the higher the risk of invasion by the bacterial hordes.

3. Worried about off flavors? Decant, decant, decant. You'll be doing at least 2 starter stages, so with the starting jar, that's 3 opportunities to decant. Most of the soluable off flavors will be in the solute!

 

[mac_1103]

Probably better to just plate up a sample and build up from there, but not everybody has the wherewithal to do that.

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 have had beers (few and far between, thank Odin) where the vessel appears to be literally boiling- like the hard boil of a kettle.

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.

 

[Bassman2003]

Well the overall goal is to get active cells in your fermentation. This thread was started because the OP had old slurries that they wanted to revive. Obviously, it is better to not start with old slurry. Period. But, homebrewers are often in this position. It stands to reason that it would be best to try to get the best cells out of the huge haystack. The path of least resistance is probably to just take a small portion of the slurry and start to grow it up as mentioned earlier in the thread. If you start small enough, new growth will outnumber old and dead cells and you will be off to the races. But small means small, like 1 milliliter or less of slurry.

 

[mashdar]

Healthy cells will naturally swamp dead ones very quickly, because healthy cells make more of themselves and will eat the dead. There's no need to get fancy. : )

 

[An Ankoù]

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.

I think many people are heavily overthinking this topic.

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.
Rather than overthinking, I think we're asking the wrong questions: here are some others:
Are the products of autolysis undesirable?
At what concentrations?
Would a yeast starter with a bit of dead yeast in it be enough to spill the beer?
Would most of these products be discarded when discarding the beer on top of the yeast starter?
Would these products get blown off by fermentation?
Would the fermenting yeast metabolise them into less undesirable substances?
Perhaps it's autolysis of the packaging yeast which is more of a problem.

 

[mac_1103]

I think we may be talking at cross purposes.

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.

 

[Miraculix]

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.
Rather than overthinking, I think we're asking the wrong questions: here are some others:
Are the products of autolysis undesirable?
At what concentrations?
Would a yeast starter with a bit of dead yeast in it be enough to spill the beer?
Would most of these products be discarded when discarding the beer on top of the yeast starter?
Would these products get blown off by fermentation?
Would the fermenting yeast metabolise them into less undesirable substances?
Perhaps it's autolysis of the packaging yeast which is more of a problem.

The co2 literally is in solution while being produced as all the metabolism is happening in solution.

If the equilibrium of dissolved co2 within the cell wall of a yeast cell has been reached, it might fall out of solution in the cell which can happen due to pressure changes or temperature changes but my guess is that this would be a big problem for the cell itself.

This is a very easy system in total. It is heavily mixed, yeast doesn't propell itself, everything floats everywhere, co2 might attach to everything. Not enough density difference for proper and easy sedimentation separation and colour doesn't tell a thing.

Use a pretty small starter, grow this one big, you're fine. We can now discuss minute details till we're all angry or tired but it won't change what's written in my last two paragraphs.

 

[Bassman2003]

I can't disagree.

 

[hottpeper13]

Maybe we should be thinking like a yeast cell; lie very still so we can be counted! I've never seen them move even when excreting the dye.

 

[Miraculix]

I literally just thought like a yeast cell:

"Ohhhh nomnom sugar!!!"

Then I thought like myself again, to some I'm probably pretty close to a yeast cell though, and reminded myself of my set daily caloric intake and decided that nom nom or beer for today would be the choice to make. So no nom noms for me today.

 

[mashdar]

If the equilibrium of dissolved co2 within the cell wall of a yeast cell has been reached, it might fall out of solution in the cell which can happen due to pressure changes or temperature changes but my guess is that this would be a big problem for the cell itself.

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)!

I can't find the HBT thread (I think Doug was on it - maybe he knows?) but here's the paper
https://pmc.ncbi.nlm.nih.gov/articles/PMC3503256/

 

[mac_1103]

Yeah, that's the one I was thinking of.