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  1. #1
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    Was It Diacetyl?

    When tasting the National Distillers Old Taylors I mentioned yesterday in the daily tasting thread, I was struck by the deep butterscotch-like taste of the whiskeys.

    Not all whiskeys from 30-40 years ago and more have that taste, but many do.

    In 2006, a special event was organised by Brown-Forman at which a number of historical bottles of Old Forester were tasted, dating back to whiskey that would have been distilled in the 1940's. John Lipman reported on the tasting on another website and said that the older ones all had a butterscotch-like taste.

    I have speculated that the use of older trees for barrel wood might have imparted this complexity but I now am wondering if fermentations then might have contained larger amounts of diacetyl than today.

    Interested readers may refer to the discussion of diacetyl in Wikipedia. Its alternate chemical names are given and other properties discussed.

    Wikipedia states that in brewing (and many beer fans are familiar with the buttery dicetyl taste in certain ales), a "diacetyl rest" is often allowed to occur after fermentation. This allows the yeast to re-absorb the diacetyl produced during active fermentation. The entry explains exactly how (in chemical terms) diacetyl is created, it is a substance that exits the yeast cells but can somehow re-enter them with a consequent neutralization of the taste associated with it.

    I wonder if Old Taylor fermentations in the 1980's and earlier might have been done in a way to favor production of large amounts of dicetyl, or at least, that is how the ferments occurred at the time for this brand and some others in the ND stable (and possibly again in some other distilleries for some other bourbons). As discussed earlier in a different context, Old Taylor may not have had this keynote taste in the 70's and earlier, so it is possible that either intentionally or otherwise, the fermentations were conducted in the 70's and 80's in a way to impart this character but not earlier.

    The fact that other bourbons had the taste suggests to me it was a traditional bourbon flavour - not the only one to be sure, but one type of flavor associated with some distilleries in Kentucky.

    In saying all the above, I am assuming of course that diacetyl can equal atmosphere pressure under sufficient heat (i.e., vaporize) but this seems clear from the Wikipedia entry which states a vaporisation temperature for diacetyl of 88 degrees C. This would be something over 200 F. and clearly since water and other compounds boiling at around that point enter a whiskey distillate so might diacetyl.

    Also, I can foresee that old-time distillers might not have wanted to rest the ferment for two to three days after its completion. Doing this might have been excessively costly and interrupted unduly the efficiency of the mashing/fermentation/distilling cycle.

    I'd be interested in anyone's comments especially brewers familiar with diacetyl and its properties or SB-ers with laboratory or chemistry experience. (Ed, any thoughts?).

    Gary
    Last edited by Gillman; 10-19-2007 at 05:03.

  2. #2
    Bourbonian of the Year 2002 and Guru
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    Re: Was It Diacetyl?

    What comes to my mind is that, with modern computer controls, distillers can be very precise about controlling fermentation. "Control" basically means using cold water (inside pipes inside the fermenters) to adjust the temperature of the fermenting mash. Controlling the fermentation temperature allows you to control exactly when the fermentation will be completed. The idea is to minimize the hold time between the completion of fermentation and the start of distillation, because there is a risk during that waiting period of unwanted microorganisms contaminating the beer.

    It may be that, in earlier days, when this science was not as evolved as it is now, there may have been more opportunity for diacetyl re-absorption. It was not deliberate, but had a happy result.

  3. #3
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    Re: Was It Diacetyl?

    Thanks for this, but if I read that Wikipedia entry right, the diacetyl rest is intended to reduce dicetyl flavor (through re-absorbtion), so if today they go straight to the distilling towers from fermentation completion, would that not tend to preserve the diacetyl flavor in the beer? Perhaps though since fermentation is controlled much more closely today than a generation ago, the answer is the yeasts do not produce much diacetyl to begin with. Certainly many brewers seem to get a handle on this, other than those who intentionally want to impart a measure of dicetyl character to their beers. Many winemakers wish to, Wikipedia gives examples of those buttery Chards. (I like those when served iced, but when served coolish or warmer they seem "too much", often).

    Gary
    Last edited by Gillman; 10-19-2007 at 12:45.

  4. #4
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    Re: Was It Diacetyl?

    Gary,
    Your right on about the diacetyl rest.

    The issue with cold-fermented styles of beer and wine is that they need to warm up essentially to an ale/red wine fermenting temperature for a day or a few days to outgas any unwanted levels of diacetyl. Ironically, some ale styles might not consider some amount of diacetyl a problem, yet they're unlikely to develop/retain much because of their brewing temperatures.

    It's the crispness and cleanness desired of most lagers that make diacetyl unwanted. What that leads me to think is that distillers may have intentionally removed diacetyl in a rush to lighten whiskies that more closely emulated the light spirits that gained higher popularity beginning in the '80s.

    Roger "just brew it" Hodges

  5. #5
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    Re: Was It Diacetyl?

    Roger, thanks, but how is it then that some ales (fermented warm) have the dicetyl problem? Distillers' mashes too are fermented at ambient I think. Are certain yeasts predisposed to it or does it have to do also with certain barley malts and other forms of cereal fermentables?

    Gary

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    Re: Was It Diacetyl?

    Quote Originally Posted by Gillman View Post
    Roger, thanks, but how is it then that some ales (fermented warm) have the dicetyl problem? Distillers' mashes too are fermented at ambient I think. Are certain yeasts predisposed to it or does it have to do also with certain barley malts and other forms of cereal fermentables?

    Gary
    Every yeast has different tolerances. Somewhere in the back of my head there's something about barley strains, but not that I can dredge up sufficiently. Maybe this is a question for Jeff Renner, not us mere mortals on this whiskey/whisky forum.

    I'm curious, what ales have a diacetyl "problem?"

    I've used many yeasts as a homebrewer, most of which were cultured from a commercial source, and I've never had amounts that I thought were a problem. Commercially, for those in Seattle, Hale's would probably be my best example of a beer that exhibits a pleasantly high level of diacetyl. And, assuming that part of the skunky banana of the original Redhook was diacetyl, that would be the only example I could think of for an obnoxious level of diacetyl in a commercial ale.

    Roger

  7. #7
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    Re: Was It Diacetyl?

    Thanks, I didn't mean some have a problem, just that some commercial ales exhibit some diacetyl character in low amounts which contributes to their character (and which does not degrade in other words, I know what you mean by that skunky banana and encountered it in some early micro ales as well). In small amount, I think diacetyl can blend with malt character to be a pleasant taste, and of course this occurs with some Chardonnay wines (where the ketone blends I think with the toasted barrel flavors). Maybe too pasteurisation can prevent such degradation.

    I thought you had indicated that ales fermented warm cannot develop much diacetyl but I think I see now what you meant (or what I didn't follow the first time!), which is that for the rest to occur, it needs to take place at warm temperatures; cold will retard the rest in other words.

    I've since read that large amounts of adjunct can increase production of diacetyl - it would seem then that distillers' mashes may be particularly liable to it.

    So, how do they get rid of the effect if today distillers' beers aren't rested for a couple of days at ambient?

    I think the answer must be that fermentation science has permitted yeasts to be cultured that simply do not produce much diacetyl to begin with.

    Whereas 40 years ago, it was part of the character (I infer) of some bourbons to retain this quality due to it enhancing the flavor of the white dog and aged whiskey. Maybe the high proofs tended to preclude the breakdown of the ketones in the whiskey. And therefore I wonder if the practice then was to go to distillation also as soon as the ferment was over. Of course the risk of bacterial infection from holding the fermented beer would have been present then too.

    My thinking is perhaps the yeasts used today by distillers produce very little dicetyl and possibly this was a result of designing cleaner-tasting bourbons as you suggested.

    Gary

  8. #8
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    Re: Was It Diacetyl?

    Quote Originally Posted by Gillman View Post
    So, how do they get rid of the effect if today distillers' beers aren't rested for a couple of days at ambient?

    I think the answer must be that fermentation science has permitted yeasts to be cultured that simply do not produce much diacetyl to begin with.

    Gary
    But Gary...

    Doesn't everybody's yeast come from Jim Beam's back porch?

  9. #9
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    Re: Was It Diacetyl?

    I don't want to nitpik here but 88 celcius is only 190.4 degrees Fahrenheit. Don't know if that makes any difference in some of the points that you're making.

    Chris

  10. #10
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    Re: Was It Diacetyl?

    Thanks for this (I had doubled the 88 and added 30 in my mind), but I do not think this would make a difference because substances volatile at the temperature of water (and higher) enter the distillate, and of course so do some volatiles whose temperature is lower even than ethanol's, so this is well within that range.

    Gary

 

 

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