Evolution of Wine and Brandy Flavors in Aging Beer (Part 1)
By jason on Dec 12, 2007 in Cellaring Science, Featured
Wine and brandy flavors are common additions to the flavor profiles of cellared beers. Though usually viewed as undesirable flavors by the brewing and scientific communities, they can often be quite pleasant in the right brew (and in the right amounts). These flavors are caused by a duo of compounds called isovalerate and 2-methyl butyrate. The process by which these compounds arise is an interesting one, and it all starts with the hop flavors in your beer.
As most of you probably know, hops are primarily responsible for the bitter flavors and aromas in your beer. Hop flavor and aroma are primarily caused by two families of acids most commonly referred to as hop alpha and beta acids (alpha acids are responsible for bitter taste, beta acids contribute to hop aroma). Be sure to check out my article on hops in aging beer for more info. The first step towards winey flavors in your beer starts with the breakdown of both of these acids through oxidation.
The paper that first really explored the oxidizing of these hop bitter acids was published back in 1979 in the ASBC (American Society of Brewing Chemists) journal by R.S Williams and H.P. Wagner and was called Contribution Of Hop Bitter Substances to Beer Staling Mechanisms. This paper shows the complete chemical progression of hop acids in beer, starting with the various oxidizing agents that cleave the unstable hop acids apart to form a number of smaller acids, including acetic, isobutyric, and isovaleric acids. These smaller acids can eventually undergo further reactions to produce isovalerate and ethyl 2-methyl butyrate.
As just an aside, some of you may rember isovaleric acids from my Brettanomyces series, where it commonly brings “sweaty” or “rancid” flavors to beers conditioned (or infected) with Brett yeast. Interestingly, the presence of isovaleric acid here from aging hops is usually described more as a presence of a “cheesy” or “old hop” flavor in the beer.
I’ll finish describing this progression of the degraded hop acids in a later article, where I’ll also discuss the implications this process has for the beers in our cellars.
Jason
Hello
Just wanted to say I really like the sound of your experiments - I’ve been dipping into your blog on and off for the past few months.
I just hope you don’t get bored before some of these experiments are complete!
Boak | Dec 14, 2007 | Reply
Hi Boak, thanks for coming by. I’ve been a subscriber to your blog for the past few months too.
I’ve built this blog from day one with the long haul in mind, so I sure hope I don’t get bored too! But with so much good beer to be drank, how could I possibly get bored?
jason | Dec 17, 2007 | Reply