What are the factors that can contribute diacytel (butter flavor) in beer? I know the yeast strain and infection are two of them. Would high fermentation temperature also result in diacytel?
Not unless it stressed the yeast. Sometimes a “diacetyl rest” is done to lower the diacetyl by raising the temperature toward the end of fermentation.
High fermentation temperature is less likely to cause diacetyl production. Prematurely dropping your fermentation temperature before the yeast have reassimilated the diacetyl is a much more likely cause.
Oxidation can also cause it by oxidizing diacetyl pre-cursors post ferment.
Jamil Z says the opposite. He believes an initial high ferm temp will potentially produce a higher level of diacetyl than a cooler start.
Reducing diacetyl near the end of fermentation can be accomplished by raising the beer temp to 65F or thereabouts for a couple of days.
This is interesting. I did a batch the way i did it before, which i know is wrong, just to see. The fermentation temperature varied between 60 and 80 degrees (night and day). I wont do that again, but i was curious.
I did do a diacytel rest but maybe should have done it a few days longer. I read that highly flocculant yeast are not as good as absorbing diacytel as well, but the yeast i used (WLP400 - Belgain wit ale) says it is low flocculating.
Maybe a higher fermentation temperature causes the yeast to speed up too much and die off before they get a chance to mellow and absorb some of the butter?
I think the fluctuating temperatures are the real culprit. Many yeast strains will respond to a ‘sudden’ drop in temperature by dropping out.
I am assuming that the temperatures you gave were the ambient temps, and not the actual fermentation temperatures, but even so I would suggest you’ll have much better results if you can find a way to keep the temperature in a more narrow range.
Diacetyl is a natural part of fermentation. Alpha-acetolactic acid is transformed into diacetyl by an oxidation reaction. This is absorbed into the yeast cell and metabolized into 3,2-butanediol which has a much higher taste threshold than diacetyl. The taste threshold of diacetyl is in the ppb (parts per billion) range. Both of these reactions are increased proportional to the temperature. So the usual plan is to ferment cool to decrease diacetyl formation, then increase the temperature (about 2/3 of the way through the fermentation) to increase diacetyl metabolization. So don’t chill the fermentation too quickly. And different yeasts will produce and remove diacetyl at different rates so these are all yeast specific.
I’d have to hear an explanation for that…
An old but good article by George Fix.
http://www.brewingtechniques.com/library/backissues/issue1.2/fix.html
Great info…thanks, Jeff.
Hmm. That article was interesting. I still think a fermentation temperature of close to 85 degrees had something do to with it:
[quote]Diacetyl production and reduction are strongly influenced by temperature, and the rates for both increase as temperature increases. Thus, an ale fermented at 20 degrees C (68 degrees F) typically has a higher diacetyl peak than, say, a lager fermented at 10 degrees C (50 degrees F).
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My thinking is that the extraordinary temperature caused a spike in diacetyl that the yeast was simply not able to keep up with. I wonder if the temperature fluctuation between 55 and 85 degrees caused the yeast to flocculate early (or just plain die), resulting in an inability to convert diacetyl after fermentation.
Like i said though, that was my last haphazard brew. Going forward i am paying far closer attention to details like temperature.
Well said Tom…I couldn’t have said it any better myself. 
JZ says that a higher ferm temp produces more of the precursers that are responsible for diacetyl formation and visa versa. Therefore he recommends pitching low to supress the precursers and ultimately produce a beer with miminal diacetyl.
For pitching low, what sort of temperatures are we talking about?
Also, i notice it says raising the temperature to around 65, which is way lower than i can achieve in the hot Denver summers. The lowest i can get is 72. What sort of techniques to you all use to lower fermentation temperature in the summer?
For me, pitching low means in the 62-65 range. That’s my standard practice.
72 is still way too high. Go out and get one of those half barrel plastic tub thingies that they put kids toys in. Put your fermenter in that and then fill the tub with water. Drop a couple frozen water bottles into the water to keep things cool. Replace the water bottles as necessary.
A water bath is surprisingly efficient. You can use a sink, tub, etc.
The 65F is for lagers. A diacetyl rest for ales is usualyl just letting it sit for another day or 2 after it has reached its final gravity.
Like Denny, I also pitch my ales in the low to mid 60’s as a general rule and for lagers I like to pitch in the mid 40’s.
You will need to establish some type of fermentation control in order to make really good beer. I use a chest freezer that was modified using a collar and a digital controller. I can keep the fermentation at setpoint +/-1 degree. So I’ll pitch at 64F and set the controller for 67F.
You can also consider using a swamp cooler which is basically a large plastic bucket filled with water maintained at fermentation temp using ice. Wet towels can be wrapped around the upper portion of the fermenter and a fan can also be used to help the heat transfer process.
Thanks for the tips. I have to be careful though: This hobby has to remain spouse-approved. For at least July and August, 70 will have to be my temp.
Going back to the diacetyl though, I just got my copy of the 3rd ed of How to Brew.
[quote]“…to hot (more than 10 degrees above the nominal range) and they [yeast] indulge in an orgy of fermentation, creating excessive by-products that often ruin the flavor of the beer. High temperatures can lead to excessive levels of diacetyl.”
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(pp. 86-7)
Thinking back, I did this recipe twice very successfully, BUT i brewed it much earlier in the year, like May. There is a huge difference in ambient temperature between May and July in Colorado. In other words, i got lucky before and didn’t know why. You are right on bluesman, i need to get a grasp of fermentation temp to do anything consistent. I dabbled for a while and now i am getting serious.
YOUR part of Colorado, maybe. ;D
But yes, consistency during fermentation (pitching rate and temperatures) is the number one thing most people can do to improve their beers. I think a swamp cooler is totally adequate for most home brewers’ needs. Once you’ve calibrated it to your conditions, you can achieve very consistent results on a spouse-friendly budget.
http://seanterrill.com/2009/05/20/regulating-fermentation-temperatures/