[Wort-H.O.G.]

under 12 

[klickitat jim]

I get bubbles at 65º within 12 hrs. Id anticipate with 18 for 50º

[HoosierBrew]

Under 12 hours I'd bet.

[S. cerevisiae]

My guess is between 12 and 18 due to the reduced temperature.

[brewinhard]

A question I have been wondering about?


Why is it acceptable to repitch slurry from a harvested batch (even days after harvesting) when I am assuming those yeast are in quiescence, yet one is not wise pitching a starter in quiescence?  Haven't both depleted their ergosterol/UFA reserves during their dormancy?  Or is it just the sheer fact that when repitching a slurry one is adding such a large population of yeast cells that it really doesn't matter?

[Wort-H.O.G.]

i've not done the pitch at high krausen, but i did do the stop at about 12 hrs and cold crash in fridge then pitch next day method. that was for a lager with wlp830 at 49F and took off at about 11hrs.

[S. cerevisiae]

Or is it just the sheer fact that when repitching a slurry one is adding such a large population of yeast cells that it really doesn't matter?

Two things are going on with slurry.  The first thing is the sheer number of cells available to us.  We can afford to pitch less healthy cells because there are so many available.  Slurry places a high O₂ load on wort.

With that said, there is something we should not overlook; namely, the cells in the slurry have been through a fermentation in our brewery.  The environment within a brewery and the practices used within a brewery place selective pressure on yeast cells.  What happens over time is that a culture adapts to a brewery.   That adaptation is caused by selective pressure, or what naturalists refer to as "survival of the fittest."  Each repitch weeds out cells that cannot handle the brewery.

When people talk about the number of times that a yeast culture can be repitched.  The dynamic here is often not the yeast cells.  What limits repitching is an ever growing microbial load.  No liquid culture is 100% pure.  Every repitch is an opportunity for microflora other than the pitched yeast strain to reproduce.  The thing about top-cropped yeast is that wild yeast and bacteria do not floc to the top; therefore, top cropping can naturally purify a culture.  A nineteenth century German chemist named Max Emil Julius Delbrück referred to this process as "Natural Pure Culture."   Delbrück duked it out with Emil Christian Hansen for the hearts and minds of brewers during the early days of pure cultures.  Delbrück's argument was that Hansen's approach (single-cell culture) was too synthetic to use in a production brewery.   Hansen's answer was the Carslberg Flask, which forms the basis for the modern yeast propagators used in large craft and industrial breweries.

Getting back to top-cropped yeast, Harveys in the UK has be repitching the same top-cropped yeast culture for over fifty years.  Geary's in Maine has been repitching the same Ringwood mixed culture for 29 years.
These cultures are now the dominant microflora in their respective breweries.   

[brewinhard]

Two things are going on with slurry.  The first thing is the sheer number of cells available to us.  We can afford to pitch less healthy cells because there are so many available.  Slurry places a high O₂ on wort.

With that said, there is something we should not overlook; namely, the cells in the slurry have been through a fermentation in our brewery.  The environment within a brewery and the practices used within a brewery place selective pressure on yeast cells.  What happens over time is that a culture adapts to a brewery.   That adaptation is caused by selective pressure, or what naturalists refer to as "survival of the fittest."  Each repitch weeds out cells that cannot handle the brewery.

When people talk about the number of times that a yeast culture can be repitched.  The dynamic here is often not the yeast cells.  What limits repitching is an ever growing microbial load.  No liquid culture is 100% pure.  Every repitch is an opportunity for microflora other than the pitched yeast strain to reproduce.  The thing about top-cropped yeast is that wild yeast and bacteria do not floc to the top; therefore, top cropping can naturally purify a culture.  A nineteenth century German chemist named Max Emil Julius Delbrück referred to this process as "Natural Pure Culture."   Delbrück duked it out with Emil Christian Hansen for the hearts and minds of brewers during the early days of pure cultures.  Delbrück's argument was that Hansen's approach (single-cell culture) was too synthetic to use in a production brewery.   Hansen's answer was the Carslberg Flask, which forms the basis for the modern yeast propagators used in large craft and industrial breweries.

Getting back to top-cropped yeast, Harveys in the UK has be repitching the same top-cropped yeast culture for over fifty years.  Geary's in Maine has been repitching the same Ringwood mixed culture for 29 years.
These cultures are now the dominant microflora in their respective breweries.

While I appreciate the response, I am not sure that this explanation fully answered my question (please don't take offense).  Aren't both populations of yeast cells (a starter going to fermentation completion and a batch of beer wort fermenting to completion of which to be repitched as slurry) considered to be in quiescence?  And if so, wouldn't both of their UFA and ergosterol reserves pretty much be used up at this point, potentially making for a "not so healthy" pitch?

Thanks for helping me trying to wrap my head around this....

[RPIScotty]

I would think a "healthy" pitch would consist of the desired yeast cells and not other microflora. Under that assumption, the sheer quantity of yeast in a slurry and the fact that it has successfully fermented a batch is a plus.


Sent from my iPhone using Tapatalk

[evil_morty]

@ nearly 8 hours since pitch now.  there MIGHT be the start of something.  a little positive pressure on the airlock anyway.

[S. cerevisiae]

While I appreciate the response, I am not sure that this explanation fully answered my question (please don't take offense).  Aren't both populations of yeast cells (a starter going to fermentation completion and a batch of beer wort fermenting to completion of which to be repitched as slurry) considered to be in quiescence?  And if so, wouldn't both of their UFA and ergosterol reserves pretty much be used up at this point, potentially making for a "not so healthy" pitch?

Thanks for helping me trying to wrap my head around this....

While I appreciate the response, I am not sure that this explanation fully answered my question (please don't take offense).  Aren't both populations of yeast cells (a starter going to fermentation completion and a batch of beer wort fermenting to completion of which to be repitched as slurry) considered to be in quiescence?  And if so, wouldn't both of their UFA and ergosterol reserves pretty much be used up at this point, potentially making for a "not so healthy" pitch?

Thanks for helping me trying to wrap my head around this....

I may be wrong, but I believe that you are equating health of the pitch with the health of the fermentation.  That's not how things work.  Improved health and activity have one big advantage; namely, they reduce the lag phase.  The lag phase is the period of time between pitching the cells and the beginning of replication (i.e., the logarithmic or exponential phase).  It is not the period of time between pitching the cells and signs of fermentation.  That definition of lag phase is misnomer that is unique to the home brewing community. The lag phase is where cellular health is rebuilt by shunting O₂ and carbon to the respirative metabolic pathway for the sythesization of ergosterol and UFAs.  Quiescent cells can become healthy cells, that is, if their cell walls have not been damaged via physical forces such as shear stress and there is enough O₂ in solution.  Quiescent cells just require more time in the lag phase and more O₂ than active cells that are pitched at high krausen.

The reason why we make a starter is to shorten what I am going to refer to as time-to-own.  Time-to-own is the period of time between pitching our culture and our culturing owning the wort.  None of our breweries are sterile.  Our culture is in a battle with other microflora that reproduce at a faster rate. Sanitize is not a synonym for sterilize.  Sanitized items still harbor live vegetative cells.  These surfaces just harbor far fewer vegetative cells than they did before they were sanitized.  This battle means that we need to do whatever we can to shorten time-to-own.   We do that by shortening the lag phase and/or the exponential phase.  My method attempts to shorten the lag phase via pitching at high krausen.  Cells at high krausen are active and have higher ergosterol and UFA reserves.   Cells pitched at high krausen have already started replicating by the time that quiescent cells have reversed the morphological changes that occurred at the end of fermentation and replenished their ergosterol and UFA reserves.

While the cells from slurry and a fermented to completion starter are quiescent, they are not quite equal.  We can look at the cells in slurry as tired battle hardened soldiers and the cells in a fermented-out starter as tired untested soldiers.  The cells in slurry have been through a "real world" fermentation in our brewery.  Starter wort is not a real world medium (at least not in American breweries ).  The cells that are not going to hack it in our brewery have already been weeded out in slurry via selective pressure.   An advantage that cannot be overlooked is the sheer number of cells available in slurry.  A 2L starter contains roughly 1/10th the number of cells in a 5-gallon batch.  While the lag phase is not shorter when pitching slurry, we have more control over the length of the exponential phase; hence, shortening time-to-own.  Anyone who has ever pitched the entire cake from a fermentation has witnessed how quickly active fermentation starts.  That's because the exponential phase has almost been completely eliminated.

In end, one should look at slurry as a brewery convenience, not the end all, be all of yeast cultures.  Repitching slurry is something that we adopted from the commercial world where the practice is critical to remaining profitable in many cases.  Ideally, we want to serially repitch to place selective pressure on a culture, plate the culture for isolates, and grow new seed culture from the best performing isolate.  If we go through that process enough times, we will end up with a culture that is robust in our brewery (however, me may not care for the flavor that it produces).

[MerlinWerks]

Thanks Mark

That certainly fleshes out your response to my initial post 

[charles1968]

While I appreciate the response, I am not sure that this explanation fully answered my question (please don't take offense).  Aren't both populations of yeast cells (a starter going to fermentation completion and a batch of beer wort fermenting to completion of which to be repitched as slurry) considered to be in quiescence?  And if so, wouldn't both of their UFA and ergosterol reserves pretty much be used up at this point, potentially making for a "not so healthy" pitch?

Thanks for helping me trying to wrap my head around this....

While I appreciate the response, I am not sure that this explanation fully answered my question (please don't take offense).  Aren't both populations of yeast cells (a starter going to fermentation completion and a batch of beer wort fermenting to completion of which to be repitched as slurry) considered to be in quiescence?  And if so, wouldn't both of their UFA and ergosterol reserves pretty much be used up at this point, potentially making for a "not so healthy" pitch?

Thanks for helping me trying to wrap my head around this....

I may be wrong, but I believe that you are equating health of the pitch with the health of the fermentation.  That's not how things work.  Improved health and activity have one big advantage; namely, they reduce the lag phase.  The lag phase is the period of time between pitching the cells and the beginning of replication (i.e., the logarithmic or exponential phase).  It is not the period of time between pitching the cells and signs of fermentation.  That definition of lag phase is misnomer that is unique to the home brewing community. The lag phase is where cellular health is rebuilt by shunting O₂ and carbon to the respirative metabolic pathway for the sythesization of ergosterol and UFAs.  Quiescent cells can become healthy cells, that is, if their cell walls have not been damaged via physical forces such as shear stress and there is enough O₂ in solution.  Quiescent cells just require more time in the lag phase and more O₂ than active cells that are pitched at high krausen.

The reason why we make a starter is to shorten what I am going to refer to as time-to-own.  Time-to-own is the period of time between pitching our culture and our culturing owning the wort.  None of our breweries are sterile.  Our culture is in a battle with other microflora that reproduce at a faster rate. Sanitize is not a synonym for sterilize.  Sanitized items still harbor live vegetative cells.  These surfaces just harbor far fewer vegetative cells than they did before they were sanitized.  This battle means that we need to do whatever we can to shorten time-to-own.   We do that by shortening the lag phase and/or the exponential phase.  My method attempts to shorten the lag phase via pitching at high krausen.  Cells at high krausen are active and have higher ergosterol and UFA reserves.   Cells pitched at high krausen have already started replicating by the time that quiescent cells have reversed the morphological changes that occurred at the end of fermentation and replenished their ergosterol and UFA reserves.

While the cells from slurry and a fermented to completion starter are quiescent, they are not quite equal.  We can look at the cells in slurry as tired battle hardened soldiers and the cells in a fermented-out starter as tired untested soldiers.  The cells in slurry have been through a "real world" fermentation in our brewery.  Starter wort is not a real world medium (at least not in American breweries ).  The cells that are not going to hack it in our brewery have already been weeded out in slurry via selective pressure.   An advantage that cannot be overlooked is the sheer number of cells available in slurry.  A 2L starter contains roughly 1/10th the number of cells in a 5-gallon batch.  While the lag phase is not shorter when pitching slurry, we have more control over the length of the exponential phase; hence, shortening time-to-own.  Anyone who has ever pitched the entire cake from a fermentation has witnessed how quickly active fermentation starts.  That's because the exponential phase has almost been completely eliminated.

In end, one should look at slurry as a brewery convenience, not the end all, be all of yeast cultures.  Repitching slurry is something that we adopted from the commercial world where the practice is critical to remaining profitable in many cases.  Ideally, we want to serially repitch to place selective pressure on a culture, plate the culture for isolates, and grow new seed culture from the best performing isolate.  If we go through that process enough times, we will end up with a culture that is robust in our brewery (however, me may not care for the flavor that it produces).

I have to say, you're very good at avoiding the question and getting lost in long digressions. All you had to say was "yes" to brewinhard's first question. Slurry from an FV contains more cells than slurry from a starter simply because it has more biomass. The natural-selection argument is obfuscation.

[charles1968]

The thing about top-cropped yeast is that wild yeast and bacteria do not floc to the top; therefore, top cropping can naturally purify a culture.

I suspect this is more to do with numbers and vigour than purity. Bacteria and wild yeast can't avoid getting buoyed up into the krausen along with beer yeast, hop debris, coagulated protein and everything else - there are simply fewer of them than beer yeast cells when fermentation is at peak activity.

[charles1968]

sythesization

I think you mean synthesis..