Sunday, January 21, 2007


Butanedione, a.k.a. diacetyl, is a chemical occasionally found in beer. For most styles, it is undesired. For some styles, low levels are acceptable, but typically, high levels of butanedione (diacetyl) indicate something went wrong during the fermentation.

The first two reactions occur inside the yeast cell. They are catalyzed by yeast enzymes. The oxidation of the acetolactic acid to butanedione occurs after the acetolactic acid leaves the cell. Another fate of acetolactic acid is the formation of valine. Malt that contains high levels of valine favors the formation of more butandione.

The butanedione can be reabsorbed by the cell and enzymatically reduced to 2,3-butanediol. This usually occurs after 7-10 days, and diacetyl levels can noticeably decrease.

High levels of butanedione in the finished beer indicate either poor sanitation (which favor bacterial production of butanedione), too much oxygen, poor malt, or poor yeast.

Someday, I am going to find a procedure for the analysis of butandione. I will test all of my beer at various stages. Now all I need is the time....


Matt Jenks said...

Since the formation of diacetyl involves a decarboxylation step, do beers that have noticeable levels of diacetyl also have an overabundance of carbonation? I assume that this comes from the primary fermentation, so it would be a moot point, if my assumptions are correct.

I was reading last night that the same bacteria that make beer less palatable through diacetyl formation gives butter a better flavor (to the tongue of butter connisseurs, of which I am not) and therefore pasteurized butter is just not as good as the stuff you can buy (and presumably get sick from) in Amish country.

Also, my wife met All About Beer editor Daniel Bradford last night at her book store. She didn't know who he was until they started talking beer and my love of it. I'm just bragging to anyone who will listen.

Russ said...

"Find a procedure" as in "locate in the literature", or as in "invent one"? If the latter, may I suggest adding some kind of 1,2-diaminoarene, which should condense with diacetyl to make an aromatic ring, and that might likely be a pretty colour too.

Chemgeek said...

As I lay in bed last night, I thought to myself... I forgot to mention that diacetyl is used as artificial flavoring for margarine. Seriously, I think of stupid things like that.

Yes you are correct. It has a flavor closely associated with butter. In beer (at very low levels) it is described as a butterscotch flavor.

I am impressed with the Daniel Bradford story. Anyone who edits a beer magazine is a man's man.

Chemgeek said...

Russ, actually the former. I don't want to reinvent the wheel... but, the 1,2-diaminoarene idea sounds intriguing. There are however, several other diketones that form. Most are minor, but they may interfere.

Matt Jenks said...

If you did Russ's condensation, couldn't you then shoot it through an LC/MS and pick off the masses?

I don't know what time you were pondering the flavoring of margarine, but it was late last night that I was reading up on diacetyl's role in flavoring butter. It made sense when I read it (butyric acid and it's rancid butter smell), but the first thing I thought of was "Ah, yes, butterscotch in beer fermented too warm". See how my mind works?