Home Brew Forums

Home Brew Forums (http://www.homebrewtalk.com/forum.php)
-   Fermentation & Yeast (http://www.homebrewtalk.com/f163/)
-   -   Aging: what exactly happens? (http://www.homebrewtalk.com/f163/aging-what-exactly-happens-238095/)

o4_srt 04-07-2011 02:45 AM

Aging: what exactly happens?
 
Does the yeast clean up it's mess, or is some other process taking place?

MalFet 04-07-2011 03:20 AM

There's a lot of stuff going on.

Some of it is metabolic, as intermediate compounds get broken down by the yeast. Acetaldehyde and diacetyl come to mind immediately, but there are certainly others.

Some of it is chemical, including oxidation.

Some of it is physical, as suspended solids settle out into the trub.

"Cleaning up" is a bit simplified, but it's not all together wrong.

o4_srt 04-07-2011 03:26 AM

Quote:

Originally Posted by MalFet
There's a lot of stuff going on.

Some of it is metabolic, as intermediate compounds get broken down by the yeast. Acetaldehyde and diacetyl come to mind immediately, but there are certainly others.

Some of it is chemical, including oxidation.

Some of it is physical, as suspended solids settle out into the trub.

"Cleaning up" is a bit simplified, but it's not all together wrong.

This thread was started in an attempt to continue an off topic conversation from a now closed thread.

Has anyone actually experimented with aging on the yeast cake, vs aging without any yeast present removed by filtration, to see what role yeast plays post fermentation?

As of right now, most are speculating.

MalFet 04-07-2011 03:37 AM

Quote:

Originally Posted by o4_srt (Post 2814797)
This thread was started in an attempt to continue an off topic conversation from a now closed thread.

Has anyone actually experimented with aging on the yeast cake, vs aging without any yeast present removed by filtration, to see what role yeast plays post fermentation?

As of right now, most are speculating.

It's not really speculation. These things are readily observable.

I can't think of any particular published experiment, but I'm not sure there's need. If you have diacetyl, you need yeast to metabolize it. Same goes for acetaldehyde, some heavy alcohols, pyruvate, acetate, etc. There's a chart here.

If you don't have detectable intermediates, you don't need the yeast any more. If you do, filtration will leave you with a flawed beer. People tend to tell new brewers to leave the beer on yeast for several weeks because it's the safe bet in a "can't hurt, might help" sort of way. To say categorically either that beer needs or that it doesn't need a long fermentation is naive.

I found and skimmed through the other thread. The person responsible for getting it locked has very little understanding of yeast biology.

o4_srt 04-07-2011 03:40 AM

Quote:

Originally Posted by MalFet

It's not really speculation. These things are readily observable.

I can't think of any particular published experiment, but I'm not sure there's need. If you have diacetyl, you need yeast to metabolize it. Same goes for acetaldehyde, some heavy alcohols, pyruvate, acetate, etc. There's a chart here.

If you don't have detectable intermediates, you don't need the yeast any more. If you do, filtration will leave you with a flawed beer. People tend to tell new brewers to leave the beer on yeast for several weeks because it's the safe bet in a "can't hurt, might help" sort of way. To say categorically that beer either needs or doesn't need a long fermentation is naive.

I found and skimmed through the other thread. The person responsible for getting it locked has very little understanding of yeast biology.

Not arguing with you, in fact, it makes perfect sense, but has it ever been directly proven that it's the yeast responsible for this, and not something else? I leave all my beer in the primary for a month before I cold crash and bottle.

I'd really like to do the experiment I outlines in the previous thread, but I don't have force carb or filtration equipment.

IffyG 04-07-2011 03:41 AM

http://www.byo.com/component/resourc...harm-your-beer

As with any of the BYO/BBR 'experiments' I wouldn't take the results too seriously, but they did have results.

Quote:

The twelve experiment participants were split on whether the process yielded significant flavor differences. Six said there was either no or slight flavor difference, while five reported definite flavor differences. One was disqualified because coriander was added to one sample and not the other. However, in his submission, Hugh Brown of New Westminster, British Columbia, commented that both samples were quite good.

Of those that described a flavor difference, five reported that the racked beer tasted “cleaner” or “smoother.”

MalFet 04-07-2011 03:53 AM

Quote:

Originally Posted by o4_srt (Post 2814843)
Not arguing with you, in fact, it makes perfect sense, but has it ever been directly proven that it's the yeast responsible for this, and not something else? I leave all my beer in the primary for a month before I cold crash and bottle.

I'd really like to do the experiment I outlines in the previous thread, but I don't have force carb or filtration equipment.

The problem is that an experiment like this wouldn't prove much, if anything. Sometimes they yeast has a lot of work to do once the simple sugars have been processed, sometimes it doesn't. I've had beers be ready for bottling after a week, some have taken a month, and a few have taken much longer, all due to yeast intermediate metabolites. In all cases, the simple sugars were all consumed in the first couple of days.

Unfortunately, this experiment is logically equivalent to calculating annual beef consumption by calling a few friends and asking if they're having hamburgers for dinner tonight. Unless you can propose another chemical pathway for things like diacetyl to be broken down, I would say this stuff is relatively proven.

Edit: P.S. I hope I don't sound short or anything here. You've got a fully legitimate question, and I'm glad to see it asked.

o4_srt 04-07-2011 04:24 AM

Quote:

Originally Posted by MalFet

The problem is that an experiment like this wouldn't prove much, if anything. Sometimes they yeast has a lot of work to do once the simple sugars have been processed, sometimes it doesn't. I've had beers be ready for bottling after a week, some have taken a month, and a few have taken much longer, all due to yeast intermediate metabolites. In all cases, the simple sugars were all consumed in the first couple of days.

Unfortunately, this experiment is logically equivalent to calculating annual beef consumption by calling a few friends and asking if they're having hamburgers for dinner tonight. Unless you can propose another chemical pathway for things like diacetyl to be broken down, I would say this stuff is relatively proven.

Edit: P.S. I hope I don't sound short or anything here. You've got a fully legitimate question, and I'm glad to see it asked.

Not at all! I started this post for educational purposes, and to get away from the petty arguing in the other thread.

If no one asked questions, and performed experiments, mankind would still be in the stone ages.

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?

Indyking 04-07-2011 12:16 PM

In case someone wonders, my opinion (not proved in a brewing set up, just what makes sense to me biologically) was part of the other thread that went too off-topic and appropriately closed by the mod.

I did more research in this subject and this is the best I could find. Brewing is also science, and perhaps that is the main reason I like this hobby so much. For those who don't know, PNAS is a highly renowned journal in scientific research worldwide. It's one of my favorites. This particular article was NIH funded.

I encourage people interested in the matter to read the article. You may find it overtly technical if you don't have a cell biology or molecular biology background, but you can skip the technical aspects about the results of their experiment and read the general well accepted knowledge about Saccharomyces cerevisiae, the common brewing yeast.

They do suggest that S. cerevisiae can carry on some degree of metabolic activity after starvation (i.e. sugar depletion), albeit minimal. Note that it is a common knowledge and also stated in the article that reentry in the cell cycle and peak of metabolic activity requires re-exposure of the yeast to its energy source, which is sugar.

So, perhaps the yeast play some role in the aging process after all but every reliable scientific resource I found to date confirms it's very minor at best.

ayoungrad 04-07-2011 12:25 PM

I also enjoy homebrewing partially because of the science behind it. I was not satisfied with explanations for several things so I ponied up and bought Briggs' Brewing: Science and Practice. I have only read about 1/2 of it - it's over 800 pages. It is meant as a textbook for professional brewing but has a lot of relevance to homebrewing as well. It is definitely science-based and not experience-based. Unfortunately the science-based aspect means it is just as dry as most science texts. But it does have a few pages specific to the science of secondary fermentation (maturation).

Check it out. It could help in this discussion.


All times are GMT. The time now is 04:38 AM.

Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.