Bubbles of gas, presumably CO2, formed during sampling, producing a light foam. Both beers were bright golden yellow, with little haze. Both beers smelt of autolyzed yeast, dimethyl sulfide, Bakelite, burnt rubber, over-ripe cheese, and goat, with phenolic and sulfury notes. As the samples warmed to room temperature, the smell of hydrogen sulfide disappeared and that of butyric acid (particularly strong in C49) strengthened.Hmm, those don't sound like particularly inviting qualities. Some of this was the result of time (autolyzed yeast, goat and cheese), but I've never heard of DMS or butyric acid developing in aged beer. Sounds to me like bad beer to begin with.
I was instantly drawn to the study, but then wondered: is it really of much use? There is a trove of chemical analysis here for the nerd--esters, phenols, carbonyl compounds, hop levels and compounds, and so on. But what does this really tell us? The authors give incredibly detailed analysis, but the sum seems far less than the parts:
In summary, these two about 170-year-old bottles contained two different beers, one (C49) more strongly hopped than the other (A56) with the low α-acid yielding hop varieties common in the 19th century. Both beers exhibited typical profiles of yeast-derived flavor compounds and of phenolics. Present knowledge of the long-term chemical and microbiological stability of these compounds is not adequate to assess how closely the observed profiles indicate the original flavor of the beers. The flavors of these compounds were hidden by very high levels of organic acids, probably produced by bacterial spoilage. The composition of the microbial mixture used to produce these beers is unclear, but it probably did not include many strains producing the Pad1 enzyme responsible for the volatile phenols characteristic of wheat beers. Pad1 activity is common in wild yeast, and its absence suggests that the yeasts employed were domesticated rather than wild.These kinds of analyses will probably add some knowledge in the margins. As far as I can tell, there hasn't been a ton of study on the aging process in beers past a certain point. (Those who pay for these studies--beer companies--have wanted to know what changes happen in the normal lifetime of a beer, not what changes happen years or decades later.) So what we know by taking a snapshot like this comes with a pretty serious cloud of mystery. Personally, I think there's quite a bit of evidence from the primary sources historians have lately been studying--evidence that is more relevant to the layman's understanding of beer evolution.