So what happens to aging beer? According to research on the subject (pdf), beer contains hundreds of molecules that
"originate from the raw materials (water, malt, hops, adjuncts) and the wort production, fermentation and maturation processes. However, the constituents of freshly bottled beer are not in chemical equilibrium. Thermodynamically, a bottle of beer is a closed system and will thus strive to reach a status of minimal energy and maximal entropy. Consequently, molecules are subjected to many reactions during storage, which eventually determine the type of the aging characteristics of beer."Oxygen is the main agent of change, and it reacts with various compounds in the beer to produce different compounds over time. From a sensory perspective, this means that bitterness declines as sweetness increases and there is a slow formation of caramel or burned-sugar flavors. Oxidation, the flavor of paper or cardboard (wet paper and cardboard in the more offensive cases), and staling also steadily increase, though the rate depends on oxygen. If the beer is bottle-conditioned, you may get autolysis (when yeast cells rupture), which tastes like soy, meat, or brine. Another flavor, which researchers used to call "ribes"--it refers to black currant leaves, but means "catty"--flourishes for a time and then diminishes. Beer picks up some wonderful flavors too--the point of aging them. These are rich sherry- or port-like rounded flavors, a sense of luxurious depth, along with dark fruit notes. My guess is that different types of beers go through entirely different processes depending on the type and amount of hops, dark malts, yeast cells, alcohol, and so on, but here's a classic diagram of what happens to light lager.
Generally speaking, I was surprised at how well the Jubels held up. The first five years had the characteristic flavors of age--they were stale, sometimes slightly metallic (I noted "blood" for the '06), and a bit faded. The aroma was uniformly good--sweet and malty, inviting. The malt flavors survived as well, and in the '05 I did get a touch of sherry. There was a minor quality of rough bitterness, and I wondered if this might be from hop's beta acids, which actually increase in bitterness with oxidation.
The '04 vintage illustrated one important fact of aging beer: the cellar-keeper is wholly at the mercy of the bottles, which may have been mishandled somewhere along the line. That vintage was undrinkable. It smelled fine, but had a briny, fishy flavor that was as offensive as it sounds. Did those bottles get to hot at some point? Was there a problem when they were bottled, or with the actual batch of beer at the brewery? There are tons of factors that can affect aging beer. When I was at Full Sail last year, Jamie Emmerson gave me some bottles of stout from the brewery's stash, and he warned that it was always a crapshoot. Even tiny variances telescoped out over years can make a big difference. That only one year was bad speaks volumes about Deschutes' quality control.
The latter half decade was in surprisingly fine fettle. I was picking up hops in the aroma of each, and they mostly seemed green and piney. Interestingly, where the first five years were perfectly bright, the '08 and '09 were murky, and the '10, '11, and '12 were bright but had little speckles, perfectly held in even suspension. They were about the same in '10 and '11, and about half as many in the '12. I'd love to hear your theories on what those were.
Bill had us rate our faves but I don't know that he tallied them. Deschutes retooled the Jubel recipe a few years back, and that was evident in the more roasty recent vintages (another danger of vertical flights). I think I liked the '08 the best, though the '10, which had the most hopping left, was also nice. But the real value was observing the chemistry and seeing how the beers changed over time.