I opened a bottle from this batch yesterday and found a strong vingegary, off flavor. Nothing at all like what I experienced the first time I tried this beer. Looking through some reviews, it seems @Chico1985 had a similar experience. Just wanted to throw this out there as a warning and I was curious to see if anybody else had issues with this batch. I'm not trying to scare anybody away from this wonderful beer altogeher, I just don't want people to have a bad experience.
Oxidation shouldn't cause vinegar flavors though. That would normally indicate an acetobacter infection. On the other hand, I've never heard of an infected German beer (let alone a doppelbock). Who knows?
