Aging: what exactly happens?

[MalFet]

If I split the same batch in two, fermented them both, then immediately after fermentation removed the yeast from one via filtration, and then aged for the same length of time, then filtering the other and force carbing both, couldn't it be feasible for any taste difference to be attributed to the yeast, and nothing else?

And, if a lack of difference was noted, couldn't one deduce that yeast don't play a part in "cleaning up" post fermentation, and taste differences are due to some other process?

Sure thing, and it would be a great experiment...If you did that, you could reasonably demonstrate that they yeast is active. But, finding no difference wouldn't demonstrate that, in other circumstances, yeast aren't active. I say go for it, if you can

 

[Indyking]

These two sentences are contradictory.

Please read Briggs or the online reference I posted.

Don’t want to get too philosophical but I said it is difficult to fight against perceptions, which is very different from common facts well accepted in the scientific community.

Like in this case, the perception that yeasts clean-up after themselves after fermentation is completed. The notion is widespread here and the best I can do is to show scientific facts that challenge the perception.

I know very well we can trace the common facts well accepted in the scientific community too its very roots, like you pointed out, I just don't think it's necessary here and it's often a struggle to find them.

Here is a nice example of a common fact well accepted in the scientific community... legendary!

 

[ayoungrad]

Sure thing, and it would be a great experiment...If you did that, you could reasonably demonstrate that they yeast is active. But, finding no difference wouldn't demonstrate that, in other circumstances, yeast aren't active. I say go for it, if you can

That is the issue I guess. You will have to wait and see if your unfiltered beer has off-flavors. If it doesn't, you would have to repeat the experiment until you get a batch that does.

If they both taste the same, maybe try repeating the experiment with a lager without a diacetyl rest? Maybe pitching at higher than expected temps? Or with a yeast strain that is know to produce diacetyls.

Of course this would only answer the question for diacetyl and nothing else...

 

[remilard]

Are you suggesting that diacetyl, acetaldehyde, etc. undergo substantial redox in the absence of yeast? I've never heard such a thing, but I'd be delighted to learn it.

I'm suggesting that the only way to get rid of diacetyl is reduction, not yeast metabolism like you stated.

In beer it happens via enzymatic reduction and the enzymes come from the yeast.

 

[ayoungrad]

Don’t want to get too philosophical but I said it is difficult to fight against perceptions, which is very different from common facts well accepted in the scientific community.

Like in this case, the perception that yeasts clean-up after themselves after fermentation is completed. The notion is widespread here and the best I can do is to show scientific facts that challenge the perception.

I know very well we can trace the common facts well accepted in the scientific community too its very roots, like you pointed out, I just don't think it's necessary here and it's often a struggle to find them.

Here is a nice example of a common fact well accepted in the scientific community... legendary!

Point taken. I guess what most people are saying is that the idea that yeast play a roll in maturation is not a perception. It is a well accepted fact. The references I gave support this.

I like your article. I used to have to find all sorts of original articles like that one and it was amazing to me how far back the journals go. And, at least at the time, that they actually still had the original copies available.

 

[ayoungrad]

I'm suggesting that the only way to get rid of diacetyl is reduction, not yeast metabolism like you stated.

In beer it happens via enzymatic reduction and the enzymes come from the yeast.

According to Briggs, the yeast "readily take up and reduce" as I mentioned above. So it is an intracellular conversion. It requires yeast cells.

 

[MalFet]

I'm suggesting that the only way to get rid of diacetyl is reduction, not yeast metabolism like you stated.

In beer it happens via enzymatic reduction and the enzymes come from the yeast.

Well, perhaps I am using terminology wrong, but I have always understood "metabolism" to be a blanket term referring to intracellular activity related to energy production, including various redox reactions. Wikipedia, at least, seems to agree.

Wouldn't saying "It's not metabolism, is reduction" be like saying "I'm not making beer, I'm making a Belgian Wit"?

In any case, this is semantics. The broader question was whether diacetyl, etc., can be broken down in meaningful quantities the absence of yeast, and you don't seem to be disagreeing with me on that.

 

[ayoungrad]

FWIW... I am a broken record, but Briggs implies that many modern commerical breweries utilize enzymes and other atypical or unnnatural means of speeding up maturation. That is to say, means other than natural yeast cell processes. Homebrewers typically do not go that route (not that you couldn't).

 

[MalFet]

FWIW... I am a broken record, but Briggs implies that many modern commerical breweries utilize enzymes and other atypical or unnnatural means of speeding up maturation. That is to say, means other than natural yeast cell processes. Homebrewers typically do not go that route (not that you couldn't).

True, true, though I hear WL and Wyeast are planning to expand their repertoire of commercially available enzymes.

(I'm very jealous of your book, btw. I get a stipend for relevant book purchases from my job, and I've often wondered if I can sneak that through.)

 

[ayoungrad]

My purchase was SWMBO approved. She accepts the fact that I'm a geek.

 

[ayoungrad]

Ohhhhh-oh-oh it's magic, you know. Never believe it's not so.

I think it is impossible to read this without singing it to yourself...

 

[pjj2ba]

Unless one has filtered their beer (or cold crashed), there is plenty of yeast is suspension to metabolize any undesireable compounds (unless fermentation was REALLY bad). I don't believe at all that by being on a yeast cake this process occurs faster/better. The yeast in the cake are the ones that are less active and have settled out and likely only play a minor role in metabolizing undesireable compounds. Just found this from Fix

Highly flocculent yeast usually behave much like W-308 and can leave perceptible levels of diacetyl in beer, which is one reason why most commercial yeast strains are powdery and fully flocculate only after chilling

http://www.brewingtechniques.com/library/backissues/issue1.2/fix.html This to me suggest that yeast is suspension are much better at cleaning anything up and that early flocculation limits diacetyl removal. Hey I learned something! I had not ever considered the importance of flocculation in diacetyl levels.

I do however believe that leaving a beer longer on the cake does influence the taste. The BYO linked article clearly shows that there are differences, some were subtle others less so. This will vary with style. What was very different was what people preferred. THIS IS WHAT IT COMES DOWN TO. Try it both ways, and see which YOU like. One should not blindy follow what someone else recommends, unless you know you have the same tastes. And then one should not blindly recommend no secondary (or X, Y, Z) unless they know the other person's tastes

In my opinion, lots of homebrewer like the extra flavors from sitting on the cake longer. That is part of the reason many start to homebrew - they want stronger flavors. (perhaps a backlash to BMC beers). Me personally, I like really clean beers. I learned early on that I don't like the yeasty/bready flavors that one can get with a long yeast cake exposure, particularly if the fermenter is a bit on the warm side. 20 + yrs ago we knew that we didn't want to ferment hot, but weren't totally clued into just how important temperature is. Nowadays the novice is quickly exposed to the importance of fermentation temperature. Now that is is easier for folks to control temperature this is less of an issue.

Wine clearly changes over time in the bottle with no yeast. Some improve, some don't, some get worse. The same is true for beer. Clearly there are non-biological aspects to maturation

 

[Indyking]

Point taken. I guess what most people are saying is that the idea that yeast play a roll in maturation is not a perception. It is a well accepted fact. The references I gave support this.
.

I haven't seen the book and I plan to buy it sometime but right now it is too expensive

Does Briggs have actual published references for the part where he describes the yeast playing a significant role after fermentation is completed during the stationary phase?

Would you mind to share those references so see if I can track them down?

If he did not referenced it, it's still just perception I'm afraid. It doesn't change much my opinion but I take your points into consideration. Thanks.

 

[ayoungrad]

I absolutely agree with pjj2ba.

This is about what we like and we should brew with techniques that result in what we like.

I don't think that means we can emphatically state that certain principles are untrue. But it means we can state that certain truths may be irrelevant to achieve our own specific goals.

And yes, like wine, beer will change over time without yeast. This does not say that yeast does not change beer taste but only that there are additional factors. Wine, to my understanding, predominately changes based on oxidation reactions and theoretically, cork is porous, allowing oxidation (this is my basic understanding based on nothing but conversations with friends). I don't know if experiments have been done, but I'd be interested to know if screw-cap wine bottles "mature". I bet they do. And it's probably based on the existing oxygen in the wine (same with canned beers).

 

[remilard]

Well, perhaps I am using terminology wrong, but I have always understood "metabolism" to be a blanket term referring to intracellular activity related to energy production, including various redox reactions. Wikipedia, at least, seems to agree.

Wouldn't saying "It's not metabolism, is reduction" be like saying "I'm not making beer, I'm making a Belgian Wit"?

In any case, this is semantics. The broader question was whether diacetyl, etc., can be broken down in meaningful quantities the absence of yeast, and you don't seem to be disagreeing with me on that.

No your terminology is correct my point is that it is the enyzmatic reduction and not yeast per se. It certainly could happen outside of a yeast cell in a number of ways.

Normally yeast are involved but then normally beer has yeast in it, doesn't it?

 

[pjj2ba]

I didn't want this to get buried and thought it was important and wanted to discuss this some more.

Just found this from Fix

Highly flocculent yeast usually behave much like W-308 and can leave perceptible levels of diacetyl in beer, which is one reason why most commercial yeast strains are powdery and fully flocculate only after chilling

http://www.brewingtechniques.com/library/backissues/issue1.2/fix.html This to me suggest that yeast is suspension are much better at cleaning anything up and that early flocculation limits diacetyl removal. Hey I learned something! I had not ever considered the importance of flocculation in diacetyl levels.

This has me thinking then that we have a lot more control over diacetyl levels than we (at least I) had been thinking.

If one is using a highly flocculant strain and want low diacetyl, then once fermentations slows a little, it might be worth it to rouse the yeast a bit (I spin my carboy) to promote better breakdown of diacetyl. I often spin my carboys, to keep the yeast up and active, with the goal of getting full attentuation. Without realizing it, I was helping to reduce diacetyl as well.

Of course one can also then limit diacetyl, through yeast strain selection, opting for a less flocculant one.

Then if you want more diacetyl for certain styles, do the opposite of above and consider a cold crash as soon as your desired FG is reached.

Cool, more techniques for the toolbox.

 

[ayoungrad]

I haven't seen the book and I plan to buy it sometime but right now it is too expensive

Does Briggs have actual published references for the part where he describes the yeast playing a significant role after fermentation is completed during the stationary phase?

Would you mind to share those references so see if I can track them down?

If he did not referenced it, it's still just perception I'm afraid. It doesn't change much my opinion but I take your points into consideration. Thanks.

He did. Check out my link earlier to the google book pages.

I can't get the final google page to load that lists the relevant references from the reference that I linked. But that is the start of the chain leading back to the earliest references. Just like in Nature, Briggs references earlier works that reference earlier works, etc.

 

[ayoungrad]

Briggs:

"Frequent causes of inability to control the concentration of vicinal diketones in beer are yeast of the wrong strain or yeast in poor health perhaps accelerated by the too rapid onset of fermenter cooling, causing the yeast to seperate. If active yeast is not present diacetyl will not be reduced."

Can you tell I have the day off today??

 

[Indyking]

He did. Check out my link earlier to the google book pages.

I can't get the final google page to load that lists the relevant references from the reference that I linked. But that is the start of the chain leading back to the earliest references. Just like in Nature, Briggs references earlier works that reference earlier works, etc.

Gotcha! Thanks. But I'm interested to know if his book specifically addresses the yeast effects under starvation after maximum attenuation is reached and SG can change no longer.

 

[pjj2ba]

Briggs:

"Frequent causes of inability to control the concentration of vicinal diketones in beer are yeast of the wrong strain or yeast in poor health perhaps accelerated by the too rapid onset of fermenter cooling, causing the yeast to seperate. If active yeast is not present diacetyl will not be reduced."

Can you tell I have the day off today??

Maybe it is me, but I read this as yeast that has settled aren't good at removing diacetyl. This would argue against those who say that leaving the yeast on the cake helps to clean up - at least diacetyl. The yeast cake has little to do with it. Leaving the beer in the fermenter will help reduce diacetyl, but not because of the yeast cake.

Also then, transferring to a secondary will not result in a decreased ability to remove diacetyl

 

[ayoungrad]

Gotcha! Thanks. But I'm interested to know if his book specifically addresses the yeast effects under starvation after maximum attenuation is reached and SG can change no longer.

I'll see if I find the book in my local libraries. I have been surprised with what they have sometimes!

I really like the book. It is very expensive but I enjoy it. It is written (dry as all get out) scientifically and has well demarcated references which are listed at the end of each chapter. It satisfies my scientifically curious side. I somehow managed to throw out every basic science text that I ever owned and this provides most of the relevant info that you would find in those texts.

As far as what after maximum attenuation... his discussion of diacetyl, etc is fairly limited but it is in the section on maturation which is described to follow primary fermentation.

 

[MalFet]

This has me thinking then that we have a lot more control over diacetyl levels than we (at least I) had been thinking.

If one is using a highly flocculant strain and want low diacetyl, then once fermentations slows a little, it might be worth it to rouse the yeast a bit (I spin my carboy) to promote better breakdown of diacetyl. I often spin my carboys, to keep the yeast up and active, with the goal of getting full attentuation. Without realizing it, I was helping to reduce diacetyl as well.

Of course one can also then limit diacetyl, through yeast strain selection, opting for a less flocculant one.

Then if you want more diacetyl for certain styles, do the opposite of above and consider a cold crash as soon as your desired FG is reached.

Cool, more techniques for the toolbox.

Very interesting...I hadn't considered that either, but I like it. I wonder if the same goes for acetaldehyde.

No your terminology is correct my point is that it is the enyzmatic reduction and not yeast per se. It certainly could happen outside of a yeast cell in a number of ways.

Normally yeast are involved but then normally beer has yeast in it, doesn't it?

Forests and trees, man, forests and trees.

 

[ayoungrad]

Maybe it is me, but I read this as yeast that has settled aren't good at removing diacetyl. This would argue against those who say that leaving the yeast on the cake helps to clean up - at least diacetyl. The yeast cake has little to do with it. Leaving the beer in the fermenter will help reduce diacetyl, but not because of the yeast cake.

Also then, transferring to a secondary will not result in a decreased ability to remove diacetyl

I absolutely agree with you about the yeast cake cells. But the way I look at things is through the concept of equilibrium. Mind you this is my personal concept and I have not read it anywhere...

There is an equilibrium between flocculated cells and the amount of available sugar. When sugar levels fall, more yeast cells flocculate. If you remove the beer/sugar/suspended yeast cells from the yeast cake, a new equilibrium is set up. The suspended yeast will flocculate more rapidly than they would if there were a large number of flocculated cells on the bottom.

Yes, this is conjecture. And to me, this is the part that can be debated.

Another thing is that the idea that the yeast cake plays no active role assumes that flocculated yeast cells are completely dormant and undergo absolutely no metabolism and no active or inactive filtration processes. I'm willing to accept this but I'm just bringing it up as a possible flaw in logic.

Does anyone have a reference relevant to these ideas?

 

[Indyking]

As far as what after maximum attenuation... his discussion of diacetyl, etc is fairly limited but it is in the section on maturation which is described to follow primary fermentation.

See, the D-rest is a different history. There seems to be no reference of what exactly the yeast does after full attenuation in brewing beer. And I looked hard for it. That's why I based my theory that not much is done by the yeast after fermentation is finished based on general knowledge in yeast metabolism I found published in reliable scientific sources. I'm not saying it's the truth, just what I believe now and I will keep looking. Will hopefully start reading the book soon!

 

[pjj2ba]

I don't assume the cake yeast are totally dormant, just not terribly active, particularly compared to those in suspension.

I wouldn't transfer to a secondary until fermentation is complete so sugars won't be playing a role. Surface area could make a difference in flocculation, where more = better. If anything I would think that having the cake present might promote flocculation as there is more surface area to be attracted to. Then it becomes a personal choice, better flocculation or less yeast exposure.

 

[remilard]

Maybe it is me, but I read this as yeast that has settled aren't good at removing diacetyl. This would argue against those who say that leaving the yeast on the cake helps to clean up - at least diacetyl. The yeast cake has little to do with it. Leaving the beer in the fermenter will help reduce diacetyl, but not because of the yeast cake.

Also then, transferring to a secondary will not result in a decreased ability to remove diacetyl

That's how I read it too. Once yeast have settled, they can't reduce VDKs.

Every commercial brewery dumps the cone within a few days of fermentation. I would think the fact that diacetyl is much less common in commercial beer than homebrew would be enough to observe that having a big pile of yeast in the bottom of the fermentor isn't the key to reduced diacetyl.

 

[cruelkix]

The idea that less flocculant yeast could clean up flaws faster is HUGE! I am loving this thread. Keep it going guys.

I'm about to go big and anything that gets non-green beer out of my fermenters faster is going to be a big concern of mine. If this holds true I will definitley start to formulate my recipes using les flocculant yeast, then eaither filtering, or cold crashing early to get the suspended yeast out.

I will be doing High Gravity Beers, so time is a big enemy for me.

Good stuff!

 

[cruelkix]

That's how I read it too. Once yeast have settled, they can't reduce VDKs.

Every commercial brewery dumps the cone within a few days of fermentation. I would think the fact that diacetyl is much less common in commercial beer than homebrew would be enough to observe that having a big pile of yeast in the bottom of the fermentor isn't the key to reduced diacetyl.

It was also brought up however that large brewers add enzymes to increaase the speed. Maybe they dont care about the yeast cake becuase they are replacing the enzymes?

 

[ayoungrad]

See, the D-rest is a different history. There seems to be no reference of what exactly the yeast does after full attenuation in brewing beer. And I looked hard for it. That's why I based my theory that not much is done by the yeast after fermentation is finished based on general knowledge in yeast metabolism I found published in reliable scientific sources. I'm not saying it's the truth, just what I believe now and I will keep looking. Will hopefully start reading the book soon!

That's not how I interpret Briggs or the reference I posted. They both seem to indicate that the dealing with diacetyl can be accomplished at the end of primary or during maturation. There are always yeast cells present and there is always a small amount of sugar present (even after "completion" of primary fermentation).

 

[MalFet]

It was also brought up however that large brewers add enzymes to increaase the speed. Maybe they dont care about the yeast cake becuase they are replacing the enzymes?

Not all (not most?) commercial breweries are adding enzymes, and in any event there's no shortage of yeast in suspension. Anecdotally, I've had effective d-rests in the absence of a yeast cake.