Based on various older sources for storing beer, i.e., English ones from the mid-1800s, I occasionally do a solera-style “barrel” program where I fill a large jug with different beers and seal it for a time.
Sometimes I drink from it and top it up, especially if it is going too flat.
For the pint of beer shown, I used a full-size growler and must have had seven or eight beers in there. Some were flat but none were spoiled. One was Belgian, Chimay I think (red capsule), there was an IPA with a strong U.S. hop accent, and then some lagers and ales of various kinds. And a porter or two.
After topping up a couple of times, I left it over the summer, at room temperature, and broached it only the other day.
It was very fizzy and gushed slowly over the top even after pouring some out.
The beer was on the dry side, chocolatey with a unified savour, quite bitter, and very tasty. No acetic notes whatever, and no funky Brettanomyces taste that I could detect. Maybe there was the faintest lactic note, a fruity kind of tang.
It was absolutely superb, probably similar to some “sound old” porter stored in the vats or cisterns of the bygone London porter-brewers. I could see people drinking it as such, or blended with younger, sweeter beer.
The strong Belgian yeast notes and emphatic American hop notes were almost completely transformed by the long secondary fermentation from the cocktail of yeasts in there. The end result was just … good.
You can tell the yeasts did something unusual as the layer of cream on the beer subsisted hours after being poured (I topped it with a saucer-bottom to drink in small amounts over a couple of days). It kept a lot of fizz, too, refusing to go flat.
If I had to choose one term to describe the taste, I would say “black wine”, a term used in the pre-nitrogen dispense days to describe Guinness, in fact.
For those who know Cahors, the black wine of the Lot valley, it was rather the beer equivalent, un cousin germain.