[HighVoltageMan!]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Oxygen will go into solution similar to co2 but to a lesser degree. Yeast doesn’t have access to oxygen in the atmosphere, it needs to be available in the wort. Pure oxygen isn’t needed unless you need to exceed 8ppm. Most ale yeasts can do fine on 8ppm, although if you have an oxygen setup, you can get it to 12ppm. I found this works very well, especially on beers above 1.060 or so.  Lagers on the other hand need more oxygen.

[Richard]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

[tommymorris]

And dry yeast don’t need aeration right?

[Richard]

And dry yeast don’t need aeration right?

Correct. The oxygen is needed to synthesize sterols and other compounds, and the dry yeast already has enough of those to ferment a batch of beer.

[Village Taphouse]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

[Megary]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

This may be a dumb question…

Is there any reason to believe that swirling or rousing the fermenter actually restarts yeast that have dropped out or have otherwise given up?  I hear this a lot, but I’ve never experienced any additional activity when I have tried it.  Time mostly, but also a bump in temperature (before it’s too late) seem to be the only arm-twisting I can use to successfully encourage the yeast along.

[denny]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

Ken, the info on foam positive elements only being used once showed up many years ago. I did some informal testing and couldn't verify that it actually made a difference in my own brewing.  It's good to be aware of it,  but don't freak out.

[erockrph]

This may be a dumb question…

Is there any reason to believe that swirling or rousing the fermenter actually restarts yeast that have dropped out or have otherwise given up?  I hear this a lot, but I’ve never experienced any additional activity when I have tried it.  Time mostly, but also a bump in temperature (before it’s too late) seem to be the only arm-twisting I can use to successfully encourage the yeast along.

I don't buy it myself. If the yeast has already formed flocs and dropped out of suspension, then shaking the flocs back up isn't going to bring the yeast out of dormancy to further attenuate a wort that they already quit on.

In all likelihood this is an old brewers' tale that dates back to the days where "active fermentation" was determined by airlock activity rather than hydrometer readings. Swirling the fermenter probably knocked some CO2 out of solution and made it look like fermentation had restarted.

[Village Taphouse]

This may be a dumb question…

Is there any reason to believe that swirling or rousing the fermenter actually restarts yeast that have dropped out or have otherwise given up?  I hear this a lot, but I’ve never experienced any additional activity when I have tried it.  Time mostly, but also a bump in temperature (before it’s too late) seem to be the only arm-twisting I can use to successfully encourage the yeast along.

I don't buy it myself. If the yeast has already formed flocs and dropped out of suspension, then shaking the flocs back up isn't going to bring the yeast out of dormancy to further attenuate a wort that they already quit on.

In all likelihood this is an old brewers' tale that dates back to the days where "active fermentation" was determined by airlock activity rather than hydrometer readings. Swirling the fermenter probably knocked some CO2 out of solution and made it look like fermentation had restarted.

Imagine this:  I have S-04 running in an ale and it's on my basement floor where it's cool and after a few days fermentation stops.  Then I carry it upstairs to a warmer place and I rouse the fermenter and yes, of course I would get some bubbling because I roused the yeast and then I might allow a few hours to go by and do that again with the wort warmer and now... for another 5-6 hours I have steady blooping in my bucket of sanitizer because the yeast warmed up and knocked the gravity down a few more ticks.  Are you thinking that if I had just moved the fermenter and not roused it the yeast would warm up and do all of that final fermenting on its own?  I'm not arguing it, I'm just curious.  I hate underfermented/sweet beer.  I want a dry finish and I want my yeast to complete it's important work.  I also want to eliminate diacetyl in a yeast strain that is known for it. 

[kramerog]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

I have never seen a factual or theoretical basis for the idea that foam positive compounds can only make foam once. But even if true, I haven't seen anything that says there isn't normally a lot of foam positive compounds still available to make foam.

[denny]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

I have never seen a factual or theoretical basis for the idea that foam positive compounds can only make foam once. But even if true, I haven't seen anything that says there isn't normally a lot of foam positive compounds still available to make foam.

That was my conclusion after my tests. Even if foam positive compunds were uwwed up, there were obviously still plenty left to create good foam.

[Richard]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

I have never seen a factual or theoretical basis for the idea that foam positive compounds can only make foam once. But even if true, I haven't seen anything that says there isn't normally a lot of foam positive compounds still available to make foam.

That was my conclusion after my tests. Even if foam positive compunds were uwwed up, there were obviously still plenty left to create good foam.

I heard that in the Charlie Bamforth podcast on BeerSmith (https://beersmith.com/blog/2021/02/28/beer-foam-with-dr-charlie-bamforth-beersmith-podcast-231/). He told a story about visiting a brewery that was complaining that their beer had crappy foam, but he saw foam all over the floor in the brewery. It obviously did foam at one time, but not when it was the finished product.

[Richard]

This may be a dumb question…

Is there any reason to believe that swirling or rousing the fermenter actually restarts yeast that have dropped out or have otherwise given up?  I hear this a lot, but I’ve never experienced any additional activity when I have tried it.  Time mostly, but also a bump in temperature (before it’s too late) seem to be the only arm-twisting I can use to successfully encourage the yeast along.

I don't buy it myself. If the yeast has already formed flocs and dropped out of suspension, then shaking the flocs back up isn't going to bring the yeast out of dormancy to further attenuate a wort that they already quit on.

In all likelihood this is an old brewers' tale that dates back to the days where "active fermentation" was determined by airlock activity rather than hydrometer readings. Swirling the fermenter probably knocked some CO2 out of solution and made it look like fermentation had restarted.

Imagine this:  I have S-04 running in an ale and it's on my basement floor where it's cool and after a few days fermentation stops.  Then I carry it upstairs to a warmer place and I rouse the fermenter and yes, of course I would get some bubbling because I roused the yeast and then I might allow a few hours to go by and do that again with the wort warmer and now... for another 5-6 hours I have steady blooping in my bucket of sanitizer because the yeast warmed up and knocked the gravity down a few more ticks.  Are you thinking that if I had just moved the fermenter and not roused it the yeast would warm up and do all of that final fermenting on its own?  I'm not arguing it, I'm just curious.  I hate underfermented/sweet beer.  I want a dry finish and I want my yeast to complete it's important work.  I also want to eliminate diacetyl in a yeast strain that is known for it.

The little trickle of bubbles might just be CO2 coming out of solution, not more CO2 being generated through fermentation. The higher temperature and agitation can cause that to happen. The higher temperature will also lower the density of the beer, so you need to be sure to correct your gravity readings for that. Otherwise just the increase in temperature and agitation can make it look like fermentation started again.

[Village Taphouse]

The little trickle of bubbles might just be CO2 coming out of solution, not more CO2 being generated through fermentation. The higher temperature and agitation can cause that to happen. The higher temperature will also lower the density of the beer, so you need to be sure to correct your gravity readings for that. Otherwise just the increase in temperature and agitation can make it look like fermentation started again.

Mmm, thanks for that.  I plan to try this out on a beer that I just made yesterday.  It's fermenting robustly on the lower level and it's probably around 62-65°.  I might just bring it upstairs close to the end of fermentation and let it warm up without rousing it.  I'll watch for activity and I'll also monitor diacetyl.  This beer was made with S-04 and I know it's character of producing the "D" if the brewer isn't careful. 

[kramerog]

I also am confused about getting O2 into the solution (by aeration stone as the only way to achieve sufficient PPM)...isn't the yeast able to scavenge O2 from the foam that is at the top of the wort after swirling/stirring/etc...  That foam is pretty full of bubbles or at least it looks like a ready source of O2 that the yeast could access.

Remember that air is only ~20% oxygen. Yes, the foam is a good source but there is a limited quantity there, and most of the yeast is in the liquid and not the foam. If you shook it over and over again every hour or so after pitching, allowing the yeast to consume the dissolved oxygen between shakings, you might eventually be able to get as much as through direct oxygenation. That is a lot of work, though, and all the splashing and foaming will only reduce the ability of foam positive compounds to form a head on your finished beer. They can only make foam once.

I'm focusing on this one piece because I have never heard this before.  This is like one of those pieces of information that are highlighted by the sun as the angels sing.  So at the end of fermentation when I might rouse my fermenter to make sure that the yeast can finish it's important work or maybe I'm working with a high-floccing yeast that may have dropped before it's finished or maybe I have moved the fermenter to a warmer spot because I'm working with a yeast that's notorious for producing diacetyl and I rouse it... I am effectively reducing the chance for a big, bountiful head of foam?  That's pretty fascinating.  What would you suggest in the examples I gave to make sure the yeast had finished without reducing the ability of foam-positive compounds to form a head?  The fact that they can only make foam once could be such a huge indicator for why some beers won't keep a nice head.  Thanks for the insight.   

I have never seen a factual or theoretical basis for the idea that foam positive compounds can only make foam once. But even if true, I haven't seen anything that says there isn't normally a lot of foam positive compounds still available to make foam.

That was my conclusion after my tests. Even if foam positive compunds were uwwed up, there were obviously still plenty left to create good foam.

I heard that in the Charlie Bamforth podcast on BeerSmith (https://beersmith.com/blog/2021/02/28/beer-foam-with-dr-charlie-bamforth-beersmith-podcast-231/). He told a story about visiting a brewery that was complaining that their beer had crappy foam, but he saw foam all over the floor in the brewery. It obviously did foam at one time, but not when it was the finished product.

Sounds like a pretty extreme example (removing the foam) that doesn't support a general rule, but I have to acknowledge that I haven't listened to the podcast and Dr. Bamforth has forgotten more beer knowledge than I have ever learned.