Conditioning a function of yeast or other chemical reactions?

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verysupple

Supremely mediocre brewer
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Hi all,
I think most of us agree with and follow the idea that it's generally better to leave the beer in the fementor for a longer rather than a shorter period of time before packaging (within reason). The idea behind this is that you leave the beer in contact with a larger quantity of yeast so it conditions faster. My question is how much conditioning is a function of yeast activity and how much is other (non yeast) chemical reactions?

I know that after the exponential phase of fermentation that the yeast then metabolise undesirable compounds they produced earlier, such as diacetyl, acetaldehyde etc., but we would all have noted the difference between young beer that still contains high levels of diacetyl etc. and what I call "green beer" which has had time to reduce those compounds but still needs time for the flavours to mellow and round out. So in my mind there are two parts to conditioning - reducing unwanted compounds which takes only a few days and flavour maturation which can take from a few days to weeks.

My gut feeling is that the "mellowing" probably isn't a function of yeast metabolism but chemical reactions between other constituents of the beer. If this is true then the beer can be separated from the bulk of the yeast and packaged earlier without adversely affecting the conditioning process which has obvious positive implications for my production rate, which always seems to lag behind my consuption. :)

I've had a bit of a search and didn't find a great deal so does anyone have any info/sources regarding this?

PS. I'm not really looking for "Well, I always leave it in the FV for 3 weeks and it works for me." because we already know that works. I'm looking for the science behind beer conditioning.
 
50 views and no replies...Either I asked a really difficult question or a really dumb one not worth answering. Or maybe it's a case of TLDR.

Anyhoos, maybe I should open it up to anecdotal responses as well as scientific sources. What are people's thoughts on packaging imediately after a diacetyl rest for ales? Better to let it sit in the FV or let it condition in the bottle?
 
I think you have answered mostly your own questions and probably Friday night isnt the best time to ask :lol:
I would question a little of your assumptions "My gut feeling is that the "mellowing" probably isn't a function of yeast metabolism" but I think you have most of it nailed.
Nev
 
I think Nev is probably right, but I'm up for a bit of late-night-Friday "bottle-logic" & anecdotal shenanegins. I don't have immediate access to voluminous tomes of scientific reference, but here goes:

Once you've "fixed" the malt profile in your wort (post mash-out) & got the alpha acids isomerised in your boil, I'd be inclined to think that it's pretty "stable". I can't remember reading anything recently about degredation of hop oils etc. over time (by recently, I mean in the past 10 years). :huh:

After you have the wort stable & introduce the yeast, as a living organism, it's the only influence of change (except for oxidation) in your beer.

Compare a pasteurised bottle of beer to one that's bottle conditioned. One is "static" except for oxidation influences. The other continues to change as the remaining yeast scavenges available oxygen in the head-space, then starts to eat it's dead brethren in order to stay alive (ultimately resulting in the characteristic vegemite-taint of autolysis).

Anecdotally, I've made some absolutely HUGE beers in the past & the best ones have been bottle conditioned. The one that stands out for me was OG 1092 & I kept it in a keg @ 4C for a good 4 months, before CPBF'ing it straight from the keg (which was the secondary fermentor). When I did that, I would still have called it "green". It took a year to mellow-out, won prizes for several years & didn't start to drop-off in quality for about 8 years.

The only possible influence of change in that beer could have been yeast.

Like I said, I don't have access to science atm, just applying logic & anecdotes.....
 
[SIZE=medium]I like the question, but am a little too well “conditioned” myself to do it justice right now, but would like to have a go at your first paragraph.[/SIZE]
[SIZE=medium]First up if you are really serious about studying brewing (and maturation in particular) the best treatment of the subject I have read is Kunze, I know it’s a bit of an Ouch price but the book is the best there is on most aspects of brewing and doesn’t assume you already have a degree in brewing science, it covers the basics very thoroughly.[/SIZE]
verysupple said:
Hi all,
I think most of us agree with and follow the idea that it's generally better to leave the beer in the fementor for a longer rather than a shorter period of time before packaging (within reason). The idea behind this is that you leave the beer in contact with a larger quantity of yeast so it conditions faster. My question is how much conditioning is a function of yeast activity and how much is other (non yeast) chemical reactions?
First up let’s just for clarity, use the same terminology
Condition or Conditioning generally refers to the natural carbonation process, what most people call secondary fermentation (which it isn’t really it’s just more primary fermentation), conditioning can also be where CO2 is introduced, as is in a conditioning tank (or keg to us home brewers) by applying pressure to cold beer so it takes up the right amount of carbonation
Maturation refers to the other processes that go on in green beer to make it ready to drink.
Yeast is primarily responsible for both (with the obvious exception) but and it’s a doozey of a but; yeast can both help and harm the beer and the maturation process.
There is an old saying in brewing “We make wort and yeast makes beer” another one of my favourites “Everything you do ends up in the glass”
Which leads me to my first issue; the idea being expressed on AHB that ever longer ferments are better is wrong, dangerously so (from the point of beer quality), you should never leave a beer on the primary yeast cake for more than two weeks, and that is under ideal brewing conditions (in the dark at the right temperature for your yeast). Any longer (and a lot faster if hotter) and the yeast will start to catabolise old and dead yeast and you will see a marked increase in the lipid content of your beer and you will start to see other off flavour products.
I’m going to stick my neck out and say, if primary fermentation isn’t over in seven days you underpitched. We all know under pitching can and does cause off flavours.
There are advantages in maturing on a reasonable amount of yeast, just not old/dead yeast, the solution being to rack the beer at or near terminal gravity. Beer that is cask clear can still have 10,000 cells/mL so there is plenty there to provide the benefits of yeast contact without the drawbacks of leaving your beer on stale yeast.
To have a tilt at the last part, early in the maturation process yeast is the primary factor in the development of the beer, both for good or ill. Off flavours from underpitching or working too hot, improved flavour by reduction of unwanted components.
Later the break down products from dying yeast can add off flavours
Even later in the process other factors can play an increasing role, hop products polymerise (clump together and form lumps) hop product have an annoying habit of sticking to everything like the inside of bottles and kegs and there goes your IAPA heading back into the ranks of a mere APA...
Oxygen is the biggest chemical contributor to flavour change, there are lots of well identified oxygen related flavour faults; fortunately yeast aggressively scavenges O2 so it’s more of a problem for commercial brewers who filter and sterilise. Very sloppy brewing practice can cause problems, but you have to work at being that lazy.
There is one other family of reactions that is often overlooked, yeast excrete enzymes into the beer. Enzymes can continue working long after the yeast that made them has stopped doing much of anything. Remorseless little biological robots wandering around looking for just one more peptide to gnaw on; might be slow but the changes add up.
Other biological processes can start to show up, I doubt any home brew has just yeast living in it, or if all the yeasts are the ones we had in mind when we pitched. Over time what was an extremely small number of bugs can play a very big role in how your beer tastes, we all know about the common infections but there are literally thousands of other bugs that will take up residence and they all end up in the glass.
It’s very late; I think it’s going to be a quad shot for breakfast, I hope you take this the way it’s intended.
Mark
 
Thanks heaps for that detailed response Mark. Very insightful stuff !!!
 
I don't have Kunze (want it very much but damn right it's expensive). However I do have a couple of other texts that support the idea that there's a multitude of things going on.

As far as I can work out, conditioning and maturation are often used quite loosely by homebrewers - thus the specifics that contribute are multiple.

For example - if talking about maturation, various chemical pathways contribute to flavour changes which can be tasted as either pleasant or unpleasant depending on the taster, the beer and the level of certain compounds that are present.

When a beer is described as oxidised, it might be tasted as stale cardboard which is an unpleasant flavour in most people's psychology. However oxidation may also result in flavours like sherry and offer an amount of complexity to a big, dark beer like an Imperial stout.

Esters (not suggesting these are formed during maturation or conditioning) are an example of how the same compound may contribute flavour that is welcome in one beer at one level but most unwelcome at a different level or in a different beer. Esters are formed when alcohols combine with fatty acids. I do not pretend to understand 100% how the various metabolic pathways operate but I believe that they are begun by yeast producing specific enzymes that catalyse chemical reactions. The enzymes produced are specific to the wort composition and the chemical pathways/bonds that occur are specific to a variety of other things occurring/existing (eg production of certain alcohols at certain levels will result in associated esters and levels).

What I'm trying to say (possibly not very successfully) is that certain chemical reactions are begun by the presence of yeast. Some of these are irreversible, some (such as the production of ethanol via acetaldehyde) are not. Healthy yeast can reabsorb some compounds as you know but various other reactions will continue to occur independently depending on many factors, including oxidation, bacteria levels etc. They may result in flavours that are welcome, they may have a peak flavour point after which the beer becomes dull or 'off' or they may be downright horrible.

For me, recommending people don't remove beer from yeast too early is mostly to do with how common a fault acetaldehyde is. Leaving beer on yeast for yonks is not likely to help mellow and while autolysis is not going to make beer taste like vegemite if you don't rack on precisely the seventh day, I have noticed beers allowed to sit on primary yeast during warmer conditions for a touch too long develop an unpleasant 'yeasty' character. Thus, from my reading, I'd say your assumption (yeast plus other chemical reactions) is correct but how much is one and how much is another is dependent on so many factors.

Unsure if I just waffled on about nothing there but the question is not that simple. So many compounds formed that are reliant on so many other compounds and conditions. It starts with the wort and yeast and while what occurs early on is a direct function of the yeast, not all of those reactions require yeast to be present once they have begun.

Principles of Brewing Science by Fix has a good breakdown of various chemical pathways that occur during fermentation, how certain compounds are formed due to the presence of others and how associated flavours may present themselves in the finished beer. De Clerck also has good sections on Yeast related redox enzymes, lagering and bottle conditioning and flavours in beer including defects.
 
Thanks, guys. Good point about the distinction between conditioning and maturation. Somewhere in the back of my mind I thought there was a word for what I meant, and I meant maturation.

Particular thanks to Manticle and Mark for the brief rundown on stuff you've read from respected sources. I'd love to get Kunze but as pointed out, it's a tad expensive. I refuse to spend that much even for books I need for work. :p I think I'll have to get myself a copy of Fix though, even if some things I've read on other topics suggest it may be a bit out of date in parts.


MHB said:
<snip>

Which leads me to my first issue; the idea being expressed on AHB that ever longer ferments are better is wrong, dangerously so (from the point of beer quality), you should never leave a beer on the primary yeast cake for more than two weeks, and that is under ideal brewing conditions (in the dark at the right temperature for your yeast). Any longer (and a lot faster if hotter) and the yeast will start to catabolise old and dead yeast and you will see a marked increase in the lipid content of your beer and you will start to see other off flavour products.
I’m going to stick my neck out and say, if primary fermentation isn’t over in seven days you underpitched.

<snip>
I'm glad I'm not the only one doubting (disagreeing with?) the mentality that leaving the beer in the FV for longer is better. FWIW, I have noticed in a lot of the interviews in the BN Can You Brew It shows that the pros always say to get the beer off the yeast as soon as the diacetyl rest is finished. Now, obviously they have to think about things like freeing up the vessels for the next batch to keep the beer going out and the cash coming in, but they certainly wouldn't jeopardise the quality of their product to do it. So getting it off the yeast seems to be a two-fold benefit - higher production rate and lower chance of the risks mentioned in the quote above.

And, yes, I'm aware that the pros pitch high cell counts of high viability, high vitality yeast so they get good quality fermentations. But this is entirely achievable on a homebrew scale. My ferments never seem to throw out much in the way of acetaldehyde, fusel alcohols or other indicators of poor fermentation and always hit FG within 4 days for average strength ales. So I figure I can apply the same principles as the big guys.

This is all good because it means I should keep doing what I've always done; package it ASAP and move on to the next batch. I still want to read up on the subject of course.
 
Both Fix and de clerck are somewhat dated (de clerck is written in the 1950s) but both have a great deal of information that remains relevant. I know Fix has some distinct errors (beta and alpha amylase get mixed up at one point) - I'd presume that's an editing error but it's there nonetheless.

Great thing about the book is that it is detailed and technical enough to be useful in understanding brewing science yet not so dense and dry that an interested but not totally brewscience savvy person can approach it and learn. It's also very affordable.

De Clerck is/was available from siebel for around $70 which is a great price for a 2-volume, hardback reference text. I believe it is/was going out of print so see if you can get a hold of one sooner rather than later.

In regards to the above - If you have no noticeable acetaldehyde, no noticeable diacetyl or similar and can do a version of the test for total vdks carried out by commercial breweries, then the yeast has done its job. There's still active yeast in suspension anyway once primary is finished so the entire cake is not likely to be of benefit.

I'd go a bit further and suggest that for brewers who have pitched inadequate amounts of yeast or not oxygenated properly (or both) that that extra time on the yeast cake might be necessary (not forever but primary, then an extra 5-7 days). I know my beer improved significantly when I started doing this but it's likely the necessity for that amount of time points to other issues. A healthy fermentation should only need a couple of days post primary but if it's not that healthy, it may benefit from longer.
 
This is an interesting subject for me too as I like beers that last longer, am interested in the ageing after primary fermentation (when you can get some of the really interesting flavours into the beer), and I've been making meads, ciders and other wines that definitely benefit from ageing. I had thought it was the yeast that helped the beer or wine change with age but, as others have pointed out on AHB, 'not really', or, 'it's complicated'. Certainly in these drinks, the ageing process really helps to break down the more unpleasant components of the brew, the ones that give you headaches and really block out the other flavours, and let the more complex flavours, the tannins and the bitters and the sugars, to really become known. I'm sure the process is much the same with beer - though maybe beer producers don't always pay as much attention to these processes as they should. (I had a strong barleywine at Beer Deluxe the other week that left me feeling the effects the day after and I wonder if that was an ale that could have benefited from a much longer ageing).

But how about this - an episode of Brewing TV focusing on meadmaking; the meadmaker avoids the long ageing process by being nice to the yeast - feeding it yeast nutrient right at the start of fermentation, at high krausen, a few days after that, and again and again, periodically for a few weeks, to ensure it is healthy at 'every stage of the fermentation'. The meads he produces age quickly, over a period of weeks or a month, rather than (as is often the case) years. So maybe it really is the yeast.
 
Which leads me to my first issue; the idea being expressed on AHB that ever longer ferments are better is wrong, dangerously so (from the point of beer quality), you should never leave a beer on the primary yeast cake for more than two weeks, and that is under ideal brewing conditions (in the dark at the right temperature for your yeast). Any longer (and a lot faster if hotter) and the yeast will start to catabolise old and dead yeast and you will see a marked increase in the lipid content of your beer and you will start to see other off flavour products.
Is this still likely to be a problem even when CCing at close to 0 degrees after two weeks at around 18-19?
 
Cc on the cake for 2 weeks is no issue in my experience. However the cake is not of benefit either. Two weeks or more at warmer temps may result in some issues - again my experience.
 
If you are conditioning your beer under gladwrap with a big airspace in a plastic fermenter the sooner you bottle it or keg it the better. If you have a good airtight glass or SS fermenter you can take your time and wait till you are happy with the flavour. A lot depends on your equipment. Bottle conditioning is a lot safer.
 
wbosher said:
Is this still likely to be a problem even when CCing at close to 0 degrees after two weeks at around 18-19?
The rate of most (all?) reactions slows with lower temps. I think if it's close to 0C then extended periods of contact with the yeast will not be a problem. The problems come a lot faster at warmer (ale fermenting) temps.
 
I'm a little dubious about the consequences of leaving beer on the cake. Any metabolism that's happening down there will only affect a tiny volume of the beer unless you go out of your way to agitate the beer. The diffusional velocity of molecules created down there is less than one millimeter per day ( much less for molecules bigger than water) and there's no free convection because the temperature gradient in beer is usually inverted (warmer at the top than the bottom). So even if autolysis is occurring and putting unpleasant compounds into the beer, I'm at the very least unconvinced that they're going to get anywhere.

Edit: if you're using a heating belt, and/or you shake all hell out of the beer in the process of racking it later, then all bets are off. (A belt could create convection currents.)
 
manticle said:
In regards to the above - If you have no noticeable acetaldehyde, no noticeable diacetyl or similar and can do a version of the test for total vdks carried out by commercial breweries, then the yeast has done its job. There's still active yeast in suspension anyway once primary is finished so the entire cake is not likely to be of benefit.
If I'm concerned about a particular batch I do a diacetyl force test as described in "The Yeast Book" (White and Zainasheff). It's very easy and worth the ~50 mL for piece of mind knowing that you won't get diacetyl showing through in the final product.

For those without the book it's basically just warming a sample to 60 - 70 C for 10 - 20 min to force the precursors to degrade to diacetyl and 2,3-pentanedione. If you can't smell or taste any after doing that you know it on't come later.
 
schrodinger said:
I'm a little dubious about the consequences of leaving beer on the cake. Any metabolism that's happening down there will only affect a tiny volume of the beer unless you go out of your way to agitate the beer. The diffusional velocity of molecules created down there is less than one millimeter per day ( much less for molecules bigger than water) and there's no free convection because the temperature gradient in beer is usually inverted (warmer at the top than the bottom). So even if autolysis is occurring and putting unpleasant compounds into the beer, I'm at the very least unconvinced that they're going to get anywhere.
That may be the case, and there's usually no need to worry if for some reason you can't get the beer off the cake immediately, but if you have the choice why wouldn't you just not take the chance and as a bonus free up your equipment for more beer? :icon_cheers:
 
verysupple said:
That may be the case, and there's usually no need to worry if for some reason you can't get the beer off the cake immediately, but if you have the choice why wouldn't you just not take the chance and as a bonus free up your equipment for more beer? :icon_cheers:
Well, all true. But the OP question was whether there are benefits RE continued smoothing out of the beer's rough edges from leaving it in the primary. I suppose, by my own logic, any such activity would have to come from still-suspended yeast that would follow the beer during transfer, so you're right.
 
schrodinger said:
Well, all true. But the OP question was whether there are benefits RE continued smoothing out of the beer's rough edges from leaving it in the primary. I suppose, by my own logic, any such activity would have to come from still-suspended yeast that would follow the beer during transfer, so you're right.
Yes, when I started the thread I was asking about the possibility of benefits from prolonged exposure to yeast or if the benefit was not due to contact with the yeast. As it turns out, the "smoothing of the beer's rough edges" (maturation) doesn't require suspended yeast.
 
Verysupple, I wouldn't go that far nor be too emphatic about the role of yeast in maturation, it can be very important, but its far from the only factor to look at. I'm just cautioning about over long exposure to old yeast.

schrodinger I bet your a physicist or such like :)
I used the term catabolise rather than autolyse, same root as cannibalise, the yeast as conditions deteriorate (from the pov of reproduction) can get downright nasty in their attempts to get hold of nutrients, they will aggressively seek out old yeast and snack on dear old mum, its always easy to anthropomorphise when talking about yeast (and bee hives) but living things don't always follow the rules we want them to play by.

enough yeast in the pitch to get to terminal gravity in not more than seven days
rack the beer and let the still working yeast finish the job once you have reached terminal gravity
don't leave beer - under any conditions - on the primary yeast cake for more than two weeks
once the beer is at the point you want it, by all means crash chill, lager, filter or what ever
Mark
 

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