I also finally tasted the second year bottling. I had some corks pop out on a couple champagne bottles I didn't cork very well and the first bottle I opened was one of the ones I recorked. I didn't add any new sugar to recarbonate because I didn't think about it at the time. It was fine but lacked the benefit of carbonation. The second bottle I opened was during a side by side comparison against the one year lambic with a carbonated bottle. (I know straight lambic is typically bottled flat but it's my beer and I'll carbonate it if I want to -- and I do want to.) So here's the flavor profile of both year two, about 14 months old, against year one, now 26 months old.
The major difference between year one and two, in my mind, is the absence of viable saccharomyces in the second year. In the first year there was a good saccharomyces fermentation but after a year of sitting in acidic beer they would have mostly died off. The second year's initial fermentation was more restrained, probably driven more by brett than saccharomyces. The absence of the yeast character from a solid saccharomyces fermentation seems to have restrained the development of that delicious cherry flavor brett often produces. I've only seen that same bold cherry pie flavor in brett beers fermented out with an estery Belgian saccharomyces strain. Instead the beer had more of a funky-earthy-leathery character. I don't have good scientific basis for that conclusion, it's just my hypothesis. I added fresh saccharomyces with the third year wort so I'll see if that beer comes out with more cherry pie flavor, confirming or disproving my hypothesis.
Right now my plan for year three is to bottle off a gallon straight and blend the other two gallons I will pull with the gallon of one year and gallon of two year to produce gueuze. Originally I planned on bottling all of year three as gueuze but I think I will regret not keeping some of year three separate to be able to taste each year as a separate bottle. I go back and forth about pulling a fourth gallon on year three and putting it on fruit or dry hopping it but right now I am against the idea because I'd rather let the solera continue to accrue an older average age by leaving more aged beer behind. Plus I think I am going to need to add another gallon of wort next brew to top up the headspace after removing all that trub from the first couple of years, so that will pull down the average age in the solera. I don't know, I will probably change my mind on each of these points a few times in between now and December.