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Diacetyl or infection

Discussion in 'All Grain Brewing' started by Drewgong, 29/8/19.

 

  1. Drewgong

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    Posted 29/8/19
    Gday fellas I brewed a Bentspoke Crankshaft ipa clone using safale us05 @ 18°c . Its been in the keg for about 2 weeks it tasted great for the first week then i noticed a slight butterscotch taste which has just gotten stronger each day You can smell it now when pouring a beer. The beer is crystal clear with perfect carbonation. Have i got my first infection or is it diacetyl ? i rushed this one into cold crash as soon as gravity readings stopped no rest as i needed the fermenter. So if the butterscotch flavour is getting stronger would that suggest infection? If it is diacetyl and i bottled it and let it warm to room temperature then leave it a few weeks Would yeast wake up and eat it ?
    It started out as one of the better beers ive ever brewed its a shame to lose it.
     
  2. MHB

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    Posted 29/8/19
    Could be both!
    There are bugs (infections) that can make Diacetyl.
    For some reason it loves to imbed it self in the plastic beer lines in keg systems, try serving the beer on a different line, or changing the line.
    In any case I would switch out the lines at the end of this keg, one of those bugs that can take a hell of a lot of killing and its often easier just to replace infected parts.
    Bit of light reading Diacetyl_Time_Line.pdf
    Mark
     

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  3. Drewgong

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    Posted 30/8/19
    T
    Thanks for that mate interesting read ill try swapping lines tomorrow.
     
  4. keine_ahnung

    joeblogsbier.com

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    Posted 18/9/19
    If it tasted good after a week, and some time later the diacetyl flavour started and kept increasing, it's verrry unlikely this is diacetyl from the fermentation.
    An ale at that temperature has already done the majority of it's conditioning (and thus breakdown of diacetyl produced during fermentation) within a week. And any fermentation-diacetyl is only going to get less.

    As Mark said, there are numerous bacteria that produce diacetyl. E.g. Pediococcus damnosis.
     
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  5. RoneMac

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    Posted 18/9/19
    A good rule of thumb: If the fault increases in intensity after fermentation is finished and the beer is chilled, it's probably an infection. If the flavour remains static with time, it is probably a process fault.
    Just a general rule. Don't bet your house on it, but it's a good start.
    MHB is spot on with the corrective action. If you have a cheap disposable part that could be an infection source, just replace it. Better to start fresh and be more vigilant in the future than to try and clean back to sanitary and risk more heartbreak if the effort wasn't 100% effective.
     
  6. Goose

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    Posted 19/10/19 at 4:32 AM
    sorry I disagree. infection can be a cause but in my experience it has always been the existence of the diacetyl precursor called AAL (alpha aceto lactate). This is formed in the fermentation process but is tasteless. It should be reabsorbed by the yeast at the end of the fermentation process and in the rest stage, but sometimes it does not get reabsorbed. AAL will gradually react to diacetyl over time if it is present and that has been the cause of by butter bomb evolution in the past.In my experience, minimising AAL is a function of yeast pitch rate and viability.

    Please check this out: https://aussiehomebrewer.com/threads/delayed-diacetyl-appearance-in-lager.64082/

    here is a simple test you can do to find out if you have AAL precursor in your beer....

    http://www.professorbeer.com/articles/diacetyl.html
     
  7. MHB

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    Posted 20/10/19 at 6:02 AM
    For that to be the cause, I suspect you would nave needed to seriously stuffed up your primary ferment.
    Massive under pitch seriously sick yeast... in any case for enough AAL to survive past a week or two of maturation your beer is going to be reeking of other yeast stress related flavours and aromas that you would have a lot of other problems beside Diacetyl (VDK's).
    The test you refer to is a pretty standard pre-packaging precaution for VDK's, when making Lager, if butter shows give the Lager another 24-48 hours at ~20oC and it will be cleaned up.
    Bacterial Diacetyl is usually low at first but grows, often its accompanied be some sour notes, if you're not sure it will certainly show as a falling pH
    Mark
     
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  8. keine_ahnung

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    Posted 21/10/19 at 10:10 PM
    Thanks Mark, I was just about to clarify this misconception, but you've covered it pretty well ;)

    As mentioned, Alpha-Acetolactat is a flavourless and odourless compound that is formed during fermentation.
    (It is formed as a downstream "byproduct" out of Pyruvat during the synthesis of Valin (an alpha acid). What is Pyruvat? One of the key compounds or stepping stones on the path from C6H12O6 (Glucose) ----> down to ---> C2H5OH (Ethanol) + CO2 + Energy! (anaerobic fermentation)
    or --> via aerobic fermentation to a much more substantial breakdown to H20 + CO2 + significantly more energy!

    Pyruvat (C3H4O3) is, in the presence of Oxygen, worked through the extremely complicated Citrat-Cycle, where amino-acids, fatty-acids, and numerous compounds that are essential to new cell production are built, broken down and transformed.

    One of these amino-acids is Valin. The amount of produced valin has a direct influence on the amount of alpha-acetolactat.

    As mentioned, alpha-acetolactat is odourless and flavourless. So what's the problem? The problem is that it is very reactive to the chemical "decarboxilisation" (splitting off of CO2) in beer. Alpha-acetolactat minus CO2 = Butandion. a.k.a Diacetyl.
    Our well known "butter" flavour/smell.

    However, Diacetyl is then taken in by the yeast, where it is further processed down to Acetoin --> then 2,3-Butandiol. (Which is flavourless and odourless). And the rate at which this happens, is of course related to the temperature.


    So, what can/should the brewer take out of this understanding of how the yeast works?? -> A few things indeed.

    1. Diacetyl isn't some mystical magical evil compound that just inconviently presents itself to annoy brewers. Brewers who understand the fermentation process DO know how much Diacetyl is going to end up in the constumer's glass, and they know when/where/how/why it's produced and how to steer these factors in the direction they want.
    Diacetyl isn't necessarily evil. In a bavarian pils, it's considered a "fault" above 0.1mg/L. In bohemian pils, it's well above this level, and is desired as such.
    There are lots of strongly hopped beers out there that are loaded with diacetyl, however most consumers don't notice it due to less experience and a shittonne of hops.

    2. An increase in the amount of alpha-acetolactat = an increase in the amount of diacetyl (which we then want the yeast to "clean up")
    So, to minimise the amount of diacetyl, these two things need to be considered. How do we produce less a-acetolactat (let's call this 2a.)? And how to we optimise the "break-down" (<- I really dislike this word in this context, as it's quite misleading. But my english is alarming rusty these days :/ ) of diacetyl into 2,3-Butandiol? (let's call this 2b.)

    2a. Again, why is a-acetolactat produced at all? It's a downstream product of the synthesis of (one of many) amino-acids. Why does the yeast produce more amino-acids??? (and this is extremely important, as it's also directly related to the amount of higher alcohols and other unpleasants in beer)
    ------> amino-acids are essential building blocks for cell growth/reproduction. The wort already has quite a lot of amino-acids in it, however when/if they aren't sufficient....it has to make it's own. (Note here, this is slightly misleading because these cycles are almost inevitable at least to some extent)

    So, two big points here: factors that stimulate growth, also stimulate this process. And a lack of amino-acids in the wort exaggerate this further! (Ever seen the term "FAN" --> Free Amino Nitrogen. That is = amino-acids)
    Factors that stimulate growth?? We already know those as brewers: oxygen and temperature are the big ones. (Pitch rate does also play a role here, but's better just to stick to pitching at a usual advised rate and varying the other factors. Because, you can't change the pitch-rate on day 3 or 5 of fermentation, but the temperature you can ;) )

    In short, cooler temps during the initial stages of fermentation reduce the level of a-alcetolactat produced.

    And, oxygen also increases the amount. But don't let this confuse you. This doesn't mean "aerate the wort less". During the first 12-24 hours, the yeast reproduces itself exponentially. It needs a shittonne of amino-acids. There's a reason why we aerate, and this is a big part of it! However, aerating after this stage is going to stimulate the citrat-cycle, producing more amino-acids, than are needed (the wort is already getting low on sugar....the yeast doesn't need to keep reproducing so much)
    In short, aerate once, and do it well.

    2b. The reaction of Diacetyl -> flavourless/odourless 2,3-Butandiol can also be influenced.
    Via: temperature, yeast strain, movement/agitation, PRESSURE, and again pitch-rate. (We'll leave pitch-rate aside for the same reasons as previously)
    That means, once the yeast has made all of the a-acetolactat that it's going to make (i.e. once the wort is exhausted of oxygen and mostly of energy sources too), slightly warmer temps accelerated the reduction of diacetyl. Hence the popularly coined "Diacetyl rest".
    (As an aside, I'm not a fan of the term, as it neglects the bigger picture. This "rest" accelerates the maturing and rounding up of numerous compounds/flavours in the beer. Not just diacetyl)
    Interestingly..... pressure has a negative affect on the "break-down" of diacetyl.

    In summary, this is why bavarian/german breweries brew their lagers at the temps they do. Lots of them still don't raise the temp for "conditioning", and opt for more time in the name of tradition. But either way, there's a good understanding of what's happening in the beer. (If there's not, they don't pass the state exam, and are then not a "brewer")


    All of this in summary also sheds light on Goose's dilemma with "increasing" diacetyl.
    To further clarify my earlier statement: Diacetyl will and can only increase in *BEER that has properly finished fermentation and conditioning, if some other non-brewers-yeast diacetyl producing organisms have entered and/or already were in the "young-beer".

    * Beer isn't "beer" until fermentation and conditioning are complete. Until then, it's actually "young-beer".
    If conditioning has properly taken place, all alpha-acetolactat has been reduced to diacetyl and then further to 2,3-Butandiol.
    And not just diacetyl. Like I keep saying, there are tonnes of compounds that need to be conditioned here. Diacetyl is taken as a benchmark of checking if the whole process has gone far enough, largely because it is detectable by humans in such low quantities. If it's gone (enough), then it's safe to say that conditioning is pretty well done.

    Reading your old post, Goose, it jumped out at me that you pitched at 12°C, and fermented at 10°C.
    I personally wouldn't have thought that this would result so extremely in the problems you seem to be having....but in light of how the yeast works, you should have better results adjusting your fermentation in the other direction :)
    12°C is pretty damn warm for a lager.

    Sorry about the long post again. But I wanted to clear up some very commonly misunderstood ideas :)
     
    Last edited: 22/10/19 at 5:52 AM
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  9. MHB

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    Posted 21/10/19 at 11:17 PM
    To avoid confusion perhaps Primary Amino Acids would be a better term than Alpha Acids which many will take to mean the main bittering component in hops, not related at all.
    The description of the Citric Acid Cycle (or Krebs cycle) in Wikipedia is a pretty good introduction, its all about producing ATP which is how cell store energy, the ATP then enters another whole series of reactions that convert Glucose to Alcohol, CO2 and Energy (Glycolysis), the ATP get recycled a bit like a battery getting recharged (iffy analogy) but that's a whole other cycle.
    Mark
     
  10. Goose

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    Posted 22/10/19 at 3:42 AM

    Thanks Mark, but I am confident in my sanitation procedures and have been as meticulous as I can in my pitching rates by stepping up to well above what the calculators say is the minimum. I had this problem almost repeatably and never ruled out bacterial infection though never tasted any other signs of it, like a hint of sourness and the problem was corrected by a re-pitch of active yeast (which I understood would unlikely correct an infected brew).

    Furthermore, my problems disappeared when I started using a smidge of Alpha Acetolactate Decarboxylase (ALDC) enzyme (just a ml in 45 litres) at commencment of fermentation.

    I remain convinced that AAL was the problem.
     
  11. keine_ahnung

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    Posted 22/10/19 at 5:43 AM
    Shit. Thanks Mark. Complete brainfart there on my part. Amino-acids! Not alpha-acids!
    *Post has been edited now ;)
     
    Last edited: 22/10/19 at 5:59 AM
  12. MHB

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    Posted 22/10/19 at 10:48 PM
    I sort of put it down to lost in translation.
    If ever you are translating "Yeast" into Spanish be very very careful, there are two quite different meanings...

    Goose
    It really is a lot more likely that when you were stepping up your yeast, you were ending up with more but less healthy yeast (given that it isn't an infection).
    Yeast farming is a lot more complex and problematic than many people thing. Unfortunately as home brewers, most of us lack the ability to do anything like accurate counts and vitality checks. Factors like the average age of the population are often totally ignored although its really important.
    Big brewers have labs and staff dedicated to keeping their yeast in peak condition, we are mostly guessing.
    If you are getting undesirable levels of VDK, even after a Diacetyl rest, especially if doing a late pitch or using ALDC is cleaning up the VDK's, I would be taking a very long hard look at my yeast management.
    A well sized pitch of healthy yeast will ferment and cleanup in 5-7 days, without remedial measures, anything else and there is a problem somewhere. It could be wort composition and the nutrients available in the wort but its much more likely to be the yeast.
    Mark
     
  13. Goose

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    Posted 23/10/19 at 1:38 AM
    very fair points and fully agree its an issue with yeast but I still ponder what I might be doing wrong with the step ups given I had precisely the same issue even pitching dried lager yeast both rehydrated and directly in different trials.

    To add, I could solve the problem by "krausening" toward the end of the fermentation or as mentioned earlier, even after the diacetyl had developed (around a month or more after kegging) by raising the temperature and adding a little fresh yeast, but I find the smidge of enzyme at the commencement of fermentation is the best insurance.

    I do realise all of these should not be necessary though.
     
  14. keine_ahnung

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    Posted 23/10/19 at 7:28 PM
    Nah...more down to the beers whilst typing it up late at night after being at work all day (where one also "has to" try beer occasionally..)

    Goose,
    Diacetyl emerging/increasing over a month after kegging is very suspect. The reaction of AAL -> Diacetyl is a chemical reaction....not an enzymatic reaction. One could say, this step on it's own, has nothing to do with yeast vitality.
    It's affected (accelerated) by: temp, lower pH, and oxygen.
    What's the pH of your beer like? What's your aeration like?

    I've never (ever) heard of "slow conversion" of AAL -> diacetyl even being mentioned as a thing, let alone a problem...but hey, it could be the case. I'll have a look in my fermentation text book tomorrow.

    If it were me, I'd being doing these steps:

    1. Pitch at 8°C, ferment at 10° until about 75% of the way through fermentation (i.e. 75% of the way between OG and FG). At this stage, turn off the cooling and let it's run it course. It'll probably warm up a bit, but shouldn't be too much. This'll accelerate all things i've been talking about above.

    Basically, optimise the fermentation. It's free, will produce a rounder crisper lager, if it fixes the problem: great. If not, you haven't lost anything either.

    2. Rule out any infections. They are products used by most competent breweries that are designed to suppress yeasts will providing an optimal environment for beer-damaging microorganisms to grow. (https://www.doehler.com/en/our-port...icrobial-detection/dmd-product-range/nbb.html)
    NBB-B changes colour when the pH falls --> extremely helpful in diagnosing the presence anaerobic bacteria in beer.
    It's not a 100% check, as there are a few bacteria that don't produce acid, but most common and most problematic ones with beer do (especially then ones that produce diacetyl)

    3. Look into your mash (well, Point 3 is kinda irrelevant, you should always be doing this).
    Most people overlook the importance of the mash for a good fermentation. At the end of the day, the entire point of mashing is turn the starch in malt into some kind of fermentable medium. If that medium is suboptimal to fement, then the problem lies with the mash, not the yeast.
    Same goes for high FG.....it's a function of the mash, SIGNIFICANTLY more than the yeast.
     
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