Tips on separating dead yeast from fresh ?

[mac_1103]

living yeast does not magically float and dead yeast does not magically flocculate and sink

This is true, but dead cells are denser than live cells and so will sink somewhat faster once you stop stirring or shaking a culture. The problem is that it's just not a very clean or efficient separation method. Wait a little too long and you'll lose the better flocculating but viable cells; don't wait long enough and you'll keep too many dead cells.

Centrifugation through dense media is a very effective laboratory method of separating live cells from dead, but obviously beyond the reach of the average home brewer.

 

[Bassman2003]

I think you guys need to take a chill pill! I don't disagree that Hotpepper's approach of getting a very small sample and letting the live cells outcompete by growing it up from there is perfectly viable. But the shake/stir then settle is just another form of that approach as you would then proceed to grow additional cells from the wort you just decanted. So a similar outcompete would take place.

If you take a sample off of the floor who knows what you will get (flocc or non-flocc, dead or half alive) so why not do a vitality test first to get 'the live ones'? The amount of live cells after 6+ months will be small, so probably a close approximation to a sample taken from sediment.

Again, working with 6+ month old slurries is obviously not SOP for a healthy yeast bank unless you have oxygen purged yeast brinks and that is pushing it.

 

[Miraculix]

This is true, but dead cells are denser than live cells and so will sink somewhat faster once you stop stirring or shaking a culture. The problem is that it's just not a very clean or efficient separation method. Wait a little too long and you'll lose the better flocculating but viable cells; don't wait long enough and you'll keep too many dead cells.

Centrifugation through dense media is a very effective laboratory method of separating live cells from dead, but obviously beyond the reach of the average home brewer.

I don't think that dead cells are denser m general. They brake apart, the pieces have different sizes, each part probably with different densities... We're talking cellular level here, these pieces are small. They float around with the slightest current occurring.

Just take a small portion from the sludge and let it grow. That's btw. The real beauty of slants. The portion is small and after multiple steps, the dead part of yeast is really small and neglactable.

 

[Miraculix]

I think you guys need to take a chill pill! I don't disagree that Hotpepper's approach of getting a very small sample and letting the live cells outcompete by growing it up from there is perfectly viable. But the shake/stir then settle is just another form of that approach as you would then proceed to grow additional cells from the wort you just decanted. So a similar outcompete would take place.

If you take a sample off of the floor who knows what you will get (flocc or non-flocc, dead or half alive) so why not do a vitality test first to get 'the live ones'? The amount of live cells after 6+ months will be small, so probably a close approximation to a sample taken from sediment.

Again, working with 6+ month old slurries is obviously not SOP for a healthy yeast bank unless you have oxygen purged yeast brinks and that is pushing it.

All good mate, no big feelings involved on my side. I just like to clarify things, either I learn something or the others learn something.

 

[mac_1103]

We're talking cellular level here, these pieces are small.

Oversimplifying quite a bit, but... cell dies and lyses; cytoplasm is basically soluble; membranes basically float; nuclei are very dense compared to intact cells; that's what falls out faster.

 

[Bassman2003]

All good mate, no big feelings involved on my side. I just like to clarify things, either I learn something or the others learn something.

So what did you clarify?

 

[SanPancho]

Sorry, but it doesn't work that way.

getting back into this as i noticed something that seems to go against your insistence that yeast are not motile. i had a semi-old starter of 3-4 months, made up 0.8L of wort and got that to spinning the day before i brewed. yada yada yada, i come back early the next morning and what do i see? wort is just reaching the point of being visibly active, i.e. its getting a cloudy look to it, with bubbles and foam starting to appear on the top. obviously, the live yeast in that starter are getting to work.

but what do i see at the bottom? a layer of yeast. not nearly as much as i pitched, but its there. no doubt about it.

i come back after lunch and now the wort is thick and opaque. what's on the bottom? same layer of yeast.

now before we get sidetracked, i let the wort settle for about 3 hours before racking. what very little trub did get picked up is yellow/golden, easily distinguished from white yeast. its not trub.

i have my own idea of what this indicates, but since you are adamant that dead yeast cannot be separated from living/active yeast I would offer you the chance to describe/explain the situation first.

what are we seeing here?

 

[mac_1103]

Let's not confuse or sidetrack things with semantics. Yeast can be moved, but they do not move themselves. They are not motile organisms. They have no flagellae or other structures associated with locomotion in microbes.

 

[Miraculix]

Let's not confuse or sidetrack things with semantics. Yeast can be moved, but they do not move themselves. They are not motile organisms. They have no flagellae or other structures associated with locomotion in microbes.

Yep, that's it.

 

[SanPancho]

Yep, that's it.

you're both tilting at wind mills.

see last three lines of the post if you actually intend to respond to the actual posed question and not just misdirect into "semantics"

 

[Mr. Vern]

Body Yeast Collector maybe?

Jokes aside, I am in the "dilute to oblivion" camp by using a baby starter and stepping up. Sure, some dead yeast provide nutrients but there will be flavors there too. Autolysis gives off protein and lipids, both of which have flavor which may or may not be desired.

 

[Miraculix]

you're both tilting at wind mills.

see last three lines of the post if you actually intend to respond to the actual posed question and not just misdirect into "semantics"

I have already said everything, if you think you know better, your choice.

 

[Mr. Vern]

Somewhat Off Topic, has anyone seen McMullan? Smart dude who could break this down intelligently, I always appreciated his yeast health input.

i have my own idea of what this indicates, but since you are adamant that dead yeast cannot be separated from living/active yeast I would offer you the chance to describe/explain the situation first.

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.

A cold crash or settling routine is effective at grabbing enough active yeast and less dead flavor to continue brewing.

I guess the big question is, does it affect your beer in a way that you dislike? Your technique is sufficient, providing a lot of new cells in the reproduction stage. But there will always be *some* dead cells left from the previous storage. It might matter for someone with a goal of the 1st place medal, it probably does not matter to people like me who just want to drink tasty brew.

 

[mac_1103]

see last three lines of the post if you actually intend to respond to the actual posed question and not just misdirect into "semantics"

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.

 

[Bassman2003]

Teaching moment here. We can agree that yeast do not have arms, legs or wings but in a typical ale fermentation they wind up at the top of the liquid. How do they get there without any motion in the wort or fermentation vessel? Honest question. Convection from metabolism?

 

[day_trippr]

CO2 production will surely carry yeast cells upward.
And then there's thermal current from the heat of fermentation...

Cheers!

 

[mac_1103]

in a typical ale fermentation they wind up at the top of the liquid

CO2 production will surely carry yeast cells upward.

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.

 

[day_trippr]

What?

 

[Miraculix]

Teaching moment here. We can agree that yeast do not have arms, legs or wings but in a typical ale fermentation they wind up at the top of the liquid. How do they get there without any motion in the wort or fermentation vessel? Honest question. Convection from metabolism?

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.

 

[Bassman2003]

Thanks. So this supports the theory that the "live" cells are up and around and the "dead" cells drop to the bottom relatively quickly. The live cells creating propulsion with their metabolism & CO2 creation and the dead cells doing nothing but being randomly propelled and sinking. Flocculation being when the live cells quit eating and propelling themselves and eventually sink to the bottom. Not dead, but full/tired.

 

[mac_1103]

The live cells creating propulsion with their metabolism & CO2 creation and the dead cells doing nothing but being randomly propelled and sinking.

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.

 

[Miraculix]

Thanks. So this supports the theory that the "live" cells are up and around and the "dead" cells drop to the bottom relatively quickly. The live cells creating propulsion with their metabolism & CO2 creation and the dead cells doing nothing but being randomly propelled and sinking. Flocculation being when the live cells quit eating and propelling themselves and eventually sink to the bottom. Not dead, but full/tired.

The CO2 gets out of solution, not out of the yeast cells itself

What I said supports only that there is a huge mess of everything inside because everything gets swirled around by rising bubbles. Doesn't matter if it's dead or alive.

 

[Bassman2003]

The CO2 gets out of solution, not out of the yeast cells itself

What I said supports only that there is a huge mess of everything inside because everything gets swirled around by rising bubbles. Doesn't matter if it's dead or alive.

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?

 

[odie]

so...on the yeast not being "mobile"...

I'm doing a Belgian Quad...it ran about a week and the air lock stopped bubbling. I racked it to a keg along with the yeast cake. I then added 1# brown sugar and 1# candi syrup.

Is all the yeast just sitting at the bottom? Do I need to shake the crap outta the keg to mix up all the yeast to get it started again?

 

[mac_1103]

If the CO2 is created by the yeast, it would be coming from them, not the wort.

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?

 

[odie]

When I use clear FV...I can see a mad flurry of yeast flying all over the place...is this the yeasts moving themselves or convection currents?

 

[mac_1103]

is this the yeasts moving themselves or convection currents?

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.

 

[mac_1103]

The CO2 gets out of solution, not out of the yeast cells itself

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.

 

[Rish]

I just like to watch. I don't really care why.

 

[Bassman2003]

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?

Good points.