Aging: what exactly happens?

ayoungrad said:

Back to the debate...

Did you read through the prior google reference? That reference seems to be the basis for Briggs' stance on the maturation process. What about the reference do you not find to be "convincing scientific support"?

What do you need to convince yourself that yeast cells aid in secondary maturation? What is it, specifically, that you are looking for? I feel like I have provided fairly good back-up information.

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My apologies. I have not had time to track down any of the google references. I'm not sure how useful they would be anyway since they seem to apply more to the D-rest, but I will take a look when I can.

I'm not talking about secondary maturation either. I'm talking specifically about that aging process in Ales where there seems to be a improvement in beer quality if the beer is allowed to rest for prolonged periods of time after fermentation is completed (Final SG is reached).

The "convincing scientific support" I talked about here and in the other thread that was closed refers to scientific articles I showed that confirm that S. cerevisiae activity and metabolism decreases dramatically at starvation in situations different from homebrewing. In our case, starvation means depletion of fermentable sugars, which is essentially their source of energy.

I don't think the book addresses that specifically. That's what I’m trying to find out.

ayoungrad said:

To add to this... Give us a reference that specifically disputes the idea that yeasts play an active role in secondary fermentation.

I have never seen one. But I'm happy to read one if you've got it.

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+1.

Indyking, you keep making references to your "reliable scientific references", but don't give us any kind of reference to follow. Citations or they don't exist.

Also, you keep saying that you haven't seen any scientific evidence to the contrary, but ayoungrad's references have been pretty solid in my book. If there is something you find problematic in them, bring it up. Everybody here is enjoying the discussion. Right now it looks like you are just ignoring the references.

Please play science with the rest of us.

MalFet said:

+1.

Indyking, you keep making references to your "reliable scientific references", but don't give us any kind of reference to follow. Citations or they don't exist.

Also, you keep saying that you haven't seen any scientific evidence to the contrary, but ayoungrad's references have been pretty solid in my book. If there is something you find problematic in them, bring it up. Everybody here is enjoying the discussion. Right now it looks like you are just ignoring the references.

Please play science with the rest of us.

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Did you see my direct link to the PNAS article? Can't remember if you post a comment about it or not.

ayoungrad's references has not shown anything that applies to Ale yeast working under starvation and what they exactly do under that situation, unless I completely missed it.

Indyking said:

Did you see my direct link to the PNAS article? Can't remember if you post a comment about it or not.

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MalFet said:

You'll have to direct me to the part of the article that says anything about yeast activity levels in a sugar-poor environment, because I can't find a darn word. The article talks about transgenerational effects of stress, and in particular compares daughters of stressed cells to naturally aged cells. I might be missing something, but I don't see a connection to the role of yeast in processing metabolic intermediates once the majority of fermentation has completed.

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That article has nothing to do with the topic at hand.

Indyking said:

ayoungrad's references has not shown anything that applies to Ale yeast working under starvation and what they exactly do under that situation, unless I completely missed it.

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They talk extensively about the processing of diacetyl after terminal gravity has been reached. Furthermore, these things are readily observable. I've got a beer going right now that, for whatever reason, spat out a lot of acetaldehyde. Over the last few days, the amount has gone down significantly (and will soon be gone completely), and yet the gravity has remained constant.

It's not a starvation environment, either. There are relatively low residual sugar levels in the beer, and don't forget that processing things like diacetyl and acetaldehyde produces energy for the yeast as well. Diacetyl and acetaldehyde are food, though less preferred to simple sugars.

Perhaps a professor at one of the brewing schools would have some insight on this. I might fire off a few emails this weekend to people at uc Davis or one of the other programs and hope I get a response.

I think there is definitely more going on in the aging process than just diacetyl reduction via yeast, the question is why and how.

Hell if I have free time tomorrow between classes, I might wander down to the bio department and start asking questions. Might track down my chem professor from last semester and pose some questions as well.

As an electrical engineering student, microbiology is not my forte, but I love science.

Indyking said:

Did you see my direct link to the PNAS article? Can't remember if you post a comment about it or not.

ayoungrad's references has not shown anything that applies to Ale yeast working under starvation and what they exactly do under that situation, unless I completely missed it.

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Your citation failed to show that yeast under starvation conditions have no effect on beer. Rather, the PNAS paper showed that passing through the stationary phase accelerates aging in yeast. This is hardly relevant to the question being asked here.

MalFet said:

That article has nothing to do with the topic at hand..

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I disagree. That article is one of the most elegant articles I have seen that deals with S. cerevisiae metabolism under starvation. Just because it was not done with samples taken from a homebrewing, it does not mean the general knowledge from it does not apply to our situation.

MalFet said:

They talk extensively about the processing of diacetyl after terminal gravity has been reached. Furthermore, these things are readily observable. I've got a beer going right now that, for whatever reason, spat out a lot of acetaldehyde. Over the last few days, the amount has gone down significantly (and will soon be gone completely), and yet the gravity has remained constant...

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.

Point taken. In fact, like I said before, I agree with that in the context of lagering, but I believe it does not apply to Ale aging.

The PNAS article confirms that yeast metabolism does not necessarily ceases upon starvation, but they do say it's dramatically reduced. What I wonder, and probably won't find a reference in a brewing context, is how much of this presumably residual metabolism after the SG has been reached influences the changes in flavor in the aging beer compared to other factors unrelated to yeast metabolism.

ayoungrad said:

It seems to me that commercial brewers use alternative methods of maturation utilizing techniques aimed at increasing throughput. To say that they dump the cone rapidly does not infer that the beer does not need to be conditioned. It just means (as I mentioned previously) that commercial brewers do not necessarily rely on yeast to clean things up.

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I know of many brewpubs that do nothing different than what many homebrewers do (they have temperature control and use gelatin, say). No chemicals, no filtration.

They all dump the yeast in the first week. I can keg almost any ale at 7 days with no chemicals/fining/filtration and they are generally flaw free (my friends like it and I win a bunch of medals).

The bottom line is, leaving the beer in contact with a pile of yeast at the bottom of the container well beyond TG is not required to make clean beer. The BBR/BYO study seemed to echo this for those who look to homebrewer kitchen science as the pinnacle of knowledge rather than industry practice and academic writings.

What nobody seems to get is that conditioning the beer in the presence of yeast does not require an inch of yeast at the bottom of the container. The yeast in suspension is generally sufficient.

IffyG said:

Your citation failed to show that yeast under starvation conditions have no effect on beer. Rather, the PNAS paper showed that passing through the stationary phase accelerates aging in yeast. This is hardly relevant to the question being asked here.

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So, show me than an article that yeast under starvation conditions have effect on beer!!! Specific to ales, which is what I'm talking about.

Wow, this thread took a turn. This is NOT as thread about autolysis and primary or secondary. We are discussing the maturation of a fermented beer and what is going on and what role(s) yeast play in this, with a bit of an emphasis on diacetyl.

I believe everyone is in agreement that diacetyl exists, it is desired in some beers and a flaw in others, and that yeast play a major role in its creation and removal

Maturation of beer flavour requires the presence of yeast as a catalyst. There are many methods of finishing that have the sole objective of prolonging the contact of beer with yeast after primary fermentation is completed. I want to emphasize that a diacetyl rest with most of the yeast lying at the bottom of the tank and not enough in suspension is of no use.

Paraphrasing
Method 1
If a very cold primary fermentation was used it involves allowing the beer temperature to rise from the controlled primary fermentation temperature of about 10°C to 15-18°C when the primary fermentation is coming to an end. ..... then the diacetyl rest would be commenced when the beer has attenuated to about SG 1023 when two-thirds of the total fermentable material in the wort has been consumed. .........

Method 2
.......When brewing ales, that should have very low diacetyl levels especially German Ales like Alt and Kölsch, the implications are to not use highly flocculent yeast and to allow an extended primary fermentation, albeit at cooler temperatures until sufficiently low diacetyl levels are reached. Yeast that settles in the cone is still removed on a daily basis.

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I interpret the "contact of beer" to simply mean there is yeast in the beer - somewhere, anywhere, and not removed by some method (filtering or cold crashing). It then goes on to say that "not enough in suspension is of no use" which I interpret to mean that settled yeast is not going to do much to reduce diacetyl.

For both of these methods above it looks to me that, at least commercially, they are relying on yeast in suspension to clean up any diacetyl. I don't see how this would change in a homebrew setting. Yeast in suspension are going to take up and metabolize diacetyl. With respect to diacetyl, yeast in suspension in a 300 bbl fermenter are going to behave the same as those in our 5 gal fermenters. There certainly is different behavior by yeast in the two systems, but I don't think the metabolism of diacetyl is one of them

So if a persons stated reason for leaving the beer on the yeast cake is to reduce diacetyl, this is not technically accurate. The remaining yeast in suspension are the ones doing the job. There are plenty of reasons why one might leave their beer on the cake, but removal of diacetyl is not one of them. It has nothing to do with if one should use a secondary or do primary only.

Indyking said:

I disagree. That article is one of the most elegant articles I have seen that deals with S. cerevisiae metabolism under starvation. Just because it was not done with samples taken from a homebrewing, it does not mean the general knowledge from it does not apply to our situation.

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So you are saying I can find any paper with a throwaway sentence (likely only there to form a tenuous link between yeast in diapause to aging) in the discussion and make it relevant to the question at hand?

No one is arguing that the metabolic activity slows during the stationary phase. IMO, the reason you are catching heat is you seem to have the idea that metabolism drops to almost nothing once the sugar runs out. That's far from reality and it's hard to believe that the yeast has no effect on it's environment when its still actively turning over it's own metabolic products.

This doesn't address any of the possible effects of yeast on beer aging, but it appears to cover a lot of ground on other contributors to aging beer.

http://nfscfaculty.tamu.edu/talcott...nd Class Presentations/Review-Beer Ageing.pdf

This thread seems to be turning argumentative, please keep the discussion on track, and let's keep it civil.

Indyking said:

So, show me than an article that yeast under starvation conditions have effect on beer!!! Specific to ales, which is what I'm talking about.

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Briggs uses the term maturation to refer to the period of continued change AFTER the completeion of primary fermentation. This is relevant for ale and lagers. I'm not sure why you have decided to separate the two. Most every comment I have made is applicable to ales and lagers.

Also, no one, that I have seen, uses the term "starvation". But maturation as I have used it from Briggs, refers to the period of time after primary fermentation, when the majority of yeast cells have flocculated. i.e. when the beer is called "green". This does not infer starvation - there is always a little sugar available. No one is ever likely to show you "starvation" condition processes in a scientific article because such a condition is irrelevant to homebrewing.

You may be right, "starvation" might result in absolute cessation of yeast cell activity given enough time. But that is not relevant here.

ayoungrad said:

Briggs uses the term maturation to refer to the period of continued change AFTER the completeion of primary fermentation. This is relevant for ale and lagers. I'm not sure why you have decided to separate the two. Most every comment I have made is applicable to ales and lagers.

Also, no one, that I have seen, uses the term "starvation". But maturation as I have used it from Briggs, refers to the period of time after primary fermentation, when the majority of yeast cells have flocculated. i.e. when the beer is called "green". This does not infer starvation - there is always a little sugar available. No one is ever likely to show you "starvation" condition processes in a scientific article because such a condition is irrelevant to homebrewing.

You may be right, "starvation" might result in absolute cessation of yeast cell activity given enough time. But that is not relevant here.

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Indeed, on page 456 in Brewing: Science and Practice says, "The concentrations of several aldehydes and vicinal diketones are influenced by yeast metabolism during fermentation and subsequent conditioning." I won't type out the rest of it since it's visible on google books, but he goes on to talk extensively about enzymatic processes that happen at various stages of a beer's life.

I'm quite curious as well about the factors that determine yeast growth curves, but perhaps that is a topic for another thread.

IffyG said:

This doesn't address any of the possible effects of yeast on beer aging, but it appears to cover a lot of ground on other contributors to aging beer.

http://nfscfaculty.tamu.edu/talcott...nd Class Presentations/Review-Beer Ageing.pdf

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At some point I have to read through this article. Good find.

But I think this article mainly deals with changes after yeast has been removed.

ayoungrad said:

At some point I have to read through this article. Good find.

But I think this article mainly deals with changes after yeast has been removed.

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Mostly, but it pertained to the original question regarding aging, so I posted it.

If starvation cannot be applied to the homebrew situation because there is always residual sugar, why the gravity reaches a point of maximum attenuation? If there was significant metabolic activity in the yeast after fermentation was completed fueled by these presumed residual sugars, one would expect the SG to move at least 1 fraction of degree Plato, which can detected by my refractometer but it does not happen! 4-5 days after a vigorous fermentation or 30 days in my ales, it does not matter, the FG is always the same. No more food. They are starved and trow into dormancy. I am however convinced that they carry on some very limited metabolic activity to sustain dormancy and prevent death like my articles showed, I'm just not sure how much of that has an influence in the quality of beer and Briggs book references to date have not specifically addressed that.

Indyking said:

I'm just not sure how much of that has an influence in the quality of beer and Briggs book references to date have not specifically addressed that.

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"The concentrations of several aldehydes and vicinal diketones are influenced by yeast metabolism during fermentation and subsequent conditioning. As a group, these generally make a negative contribution to beer flavour and aroma. An important part of fermentation management is to ensure that these compounds are reduced to acceptable concentrations." (Briggs 2004: 456)

Can't get much more specific than that.

MalFet said:

"The concentrations of several aldehydes and vicinal diketones are influenced by yeast metabolism during fermentation and subsequent conditioning. As a group, these generally make a negative contribution to beer flavour and aroma. An important part of fermentation management is to ensure that these compounds are reduced to acceptable concentrations." (Briggs 2004: 456)

Can't get much more specific than that.

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First, he does not distinguish how much of that is influenced by fermentation vs. conditioning. It's a very general and broad assessment. If 99% is influenced during fermentation and merely 1% by conditioning, the statement is right and I'm right too!
Second. There is no reference to it, if there is please show me, hopefully the actual reference will do a better job. Until referenced by a reliable scientific study, it's just perceptions based on who knows what!?!

Indyking said:

If starvation cannot be applied to the homebrew situation because there is always residual sugar, why the gravity reaches a point of maximum attenuation? If there was significant metabolic activity in the yeast after fermentation was completed fueled by these presumed residual sugars, one would expect the SG to move at least 1 fraction of degree Plato, which can detected by my refractometer but it does not happen! 4-5 days after a vigorous fermentation or 30 days in my ales, it does not matter, the FG is always the same. No more food. They are starved and trow into dormancy. I am however convinced that they carry on some very limited metabolic activity to sustain dormancy and prevent death like my articles showed, I'm just not sure how much of that has an influence in the quality of beer and Briggs book references to date have not specifically addressed that.

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Ok. Not sure how much more staying power I have, but here goes another quote from Briggs:

"Beer, at completion of primary fermentation is said to be 'green'... In order to refine green beer it must be matured or conditioned... also called 'lagering' when referring to bottom fermented beers... Traditionally, maturation involves a secondary fementation and is effected by the small amount of yeast remaining in the beer when it is transferred from the fermenting vessel. This yeast can utilize fermentable carbohydrates remaining in the beer at the end of primary fermentation...Traditionally after primary fermentation the beer would pass into the conditioning or maturation vessel and would contain 1-4 million cells/mL of beer and about [1.1% fermentable extract]..."

I can not provide any more relevant information than this.

Your article is about the life cycle of yeast cells and possible long-term viability affects of dormancy. That does not seem to be what we are discussing.

Do you have anything I can read that disputes what I have just written? I think I have answered (in quoting two consecutive pages of one book) the questions you have raised.

ayoungrad said:

Ok. Not sure how much more staying power I have, but here goes another quote from Briggs:

"Beer, at completion of primary fermentation is said to be 'green'... In order to refine green beer it must be matured or conditioned... also called 'lagering' when referring to bottom fermented beers... Traditionally, maturation involves a secondary fementation and is effected by the small amount of yeast remaining in the beer when it is transferred from the fermenting vessel. This yeast can utilize fermentable carbohydrates remaining in the beer at the end of primary fermentation...Traditionally after primary fermentation the beer would pass into the conditioning or maturation vessel and would contain 1-4 million cells/mL of beer and about [1.1% fermentable extract]..."

I can not provide any more relevant information than this.

Your article is about the life cycle of yeast cells and possible long-term viability affects of dormancy. That does not seem to be what we are discussing.

Do you have anything I can read that disputes what I have just written? I think I have answered (in quoting two consecutive pages of one book) the questions you have raised.

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Give me the page number. I will see if I can find the scientific reference for his statement or perhaps another perception.

My reference:

Brewing Science and Practice (2004) by: Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes, Roger Stevens

If you want to chase down their references, feel free. They are at the end of every chapter.

ayoungrad said:

My reference:

Brewing Science and Practice (2004) by: Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes, Roger Stevens

If you want to chase down their references, feel free. They are at the end of every chapter.

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No, you know better! I have the book in front of me! The book specifically mention the reference at the end of each paragraph for referenced information published somewhere else. Everything else are his opinions in the matter. Give me the page number!

Indyking said:

Give me the page number. I will see if I can find the scientific reference for his statement or perhaps another perception.

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Wow. Have you ever trusted anything without experiencing it for yourself?

I tend to be pretty stubborn and I would much rather learn on my own than have facts spewed at me. But man, you take the cake.

In answer to your request... pages 543-544 and more info on the pages that follow.

Indyking said:

No, you know better! I have the book in front of me! The book specifically mention the reference at the end of each paragraph for referenced information published somewhere else. Everything else are his opinions in the matter. Give me the page number!

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I wrote that before I saw your response. Relax. I knew you'd ask for a reference. I just didn't know I had to give you the page number.

You are a piece of work.

I'm done.

Indyking said:

No, you know better! I have the book in front of me! The book specifically mention the reference at the end of each paragraph for referenced information published somewhere else. Everything else are his opinions in the matter. Give me the page number!

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Have you ever written a book chapter? I have... I had to review GABAergic neurotransmission in 5 pages with fewer than 20 references. Are you telling me that the vast majority of what I wrote (and didn't get to cite owing to limitations by the publisher) are simply my opinion? Not everything that is based in science will be cited in a book chapter.

Indyking said:

First, he does not distinguish how much of that is influenced by fermentation vs. conditioning. It's a very general and broad assessment. If 99% is influenced during fermentation and merely 1% by conditioning, the statement is right and I'm right too!
Second. There is no reference to it, if there is please show me, hopefully the actual reference will do a better job. Until referenced by a reliable scientific study, it's just perceptions based on who knows what!?!

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In order of apparent relevance:
(Barry and Watson 1987)
(Debourg et al. 1993)
(Jacobson and Bernofsky 1974)
(Mielgard 1975)
(Laurent et al 1995)

When you finish reading those, let me know and I'll pull up the rest. This tome is obsessively cited, which you would know if you checked it out yourself. The bibliography is at the end.

And of course, this kind of late processing is going to be more important in some batches than in others. I'm not sure what you are measuring when you say "99%", but if you don't know how significant an impact intermediate metabolites can have on a beer's flavor then I suspect you are rather new to this.

ayoungrad said:

Wow. Have you ever trusted anything without experiencing it for yourself?

I tend to be pretty stubborn and I would much rather learn on my own than have facts spewed at me. But man, you take the cake.

In answer to your request... pages 543-544 and more info on the pages that follow.

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Thanks, just like I suspected. No reference. There isn't a single reference in pages 543-544 as a matter of fact. The book is very organized literally the way it should be, every paragraph that is based on scientific information is referenced! Much discussion... Not much progress. We are still subject to opinions not based in scientific research, most likely due to experience.

Indyking said:

No, you know better! I have the book in front of me! The book specifically mention the reference at the end of each paragraph for referenced information published somewhere else. Everything else are his opinions in the matter. Give me the page number!

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What you should be asking for is what sources cite approvingly to Briggs. To the extent that Briggs is relied upon as an authoritative source of information, it is a bit disingenuous to say all non-referenced statements are merely "his opinions in the matter." That is how academic writing works - you state an "opinion" based on your experience and the study of other works. If that opinion is picked up and cited by others as support for their opinions enough times, you begin to accept that "opinion" as fact.

IffyG said:

Have you ever written a book chapter? I have... I had to review GABAergic neurotransmission in 5 pages with fewer than 20 references. Are you telling me that the vast majority of what I wrote (and didn't get to cite owing to limitations by the publisher) are simply my opinion? Not everything that is based in science will be cited in a book chapter.

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I have wrote 2 thesis and published more than 20 articles in highly regarded journals . I'm not telling you did anything wrong, don't put words in my mouth please.

And I'm also done. It has been a good discussion. Thanks for your comments.

I'm not putting words in your mouth... you said this:

Indyking said:

The book specifically mention the reference at the end of each paragraph for referenced information published somewhere else. Everything else are his opinions in the matter. Give me the page number!

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There is no misinterpretation, it's clear that you believe anything stated without citation is a matter of opinion.

ayoungrad said:

I wrote that before I saw your response. Relax. I knew you'd ask for a reference. I just didn't know I had to give you the page number.

You are a piece of work.

I'm done.

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Don't leave ayoungrad! I'm learning too much!

I just browsed through this guy's post history, and he does this in every thread he's in. My theory, based on scientific facts, is that IndyKing is a myth. I would love to be proven wrong in this matter, but unfortunately I have an unconventional and deeply personal notion of "proof". Also, gravity is just an opinion.

We can continue this conversation, which has been fascinating, if we just stop letting ourselves get baited.

Indyking is sticking to his "opinion" with religious fervor and there is no turning the devout.

Are we in kindergarden? Why is it so hard to discuss a rather nonemotional subject like an adult?

It's not like yeast is running for president...

Thanks for ruining the thread guys.. At least a few of us learned a thing or two before it went downhill.


This thread wasn't posted to"prove" anything, merely discuss and learn. Not sure why everyone has to prove something.

Thanks for ruining the thread guys.. At least a few of us learned a thing or two before it went downhill.

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What is there left to say? The last 50 or so posts contained a mountain of evidence regarding what happens during the aging process, and some people that shall not be named simply ignored the substance of the evidence because it wasn't referenced to their liking. A statement is either true or false - whether or not someone said the exact same thing in the past is not the end all be all of veracity.

"I don't want to talk to a scientist, ya'll MF lying and getting me pissed" - ICP

Not sure if this helps or not. I have been brewing the exact same recipe for 3 year(extract bb kit). up until this year I always took a reading in 5-7 days and moved to secondary for 2-3 days to "clarify" the beer, then bottled. There was always a certain bitter flavor that bothered me and my buddy not bad but you knew it was not supposed to be there. I made the same Kit this year the only thing i did differently was w8 for 3 weeks before waiting to tame my reading. then went to secondary for 2-3 days then bottle. it is a 100% better than ever before.


I know not scientific but it was enough proof for me that aging does in fact help.

tchuklobrau said:

Not sure if this helps or not. I have been brewing the exact same recipe for 3 year(extract bb kit). up until this year I always took a reading in 5-7 days and moved to secondary for 2-3 days to "clarify" the beer, then bottled. There was always a certain bitter flavor that bothered me and my buddy not bad but you knew it was not supposed to be there. I made the same Kit this year the only thing i did differently was w8 for 3 weeks before waiting to tame my reading. then went to secondary for 2-3 days then bottle. it is a 100% better than ever before.


I know not scientific but it was enough proof for me that aging does in fact help.

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If you do not have a scientific reference for this incident, then it did not happen. Heck, you may not even actually exist. Wait, do I exist? Oh no, I've gone cross-eyed.