I've brewed 21 all grain batches with great results and have never worried about my mash pH until recently. I added 1 tablespoon of Five Star's 5.2 mash stabilizer to each of my last two beers, an ESB and American Amber for shits and giggles. Before kegging, both beers tasted young but right where they should be. Once kegged, I hooked both up to CO2 at 12 psi for a week. Upon tasting both after a week, I noticed that they developed an awful metallic mineral like taste that was not there at kegging. Since I brew 6 gallon batches, I always have some leftover in the fermenter once the keg is full, so I fill up a couple of bombers just to have around. I also tried the bombers of uncarbonated beer, and none of them have developed the terrible flavor that the kegs did.
My sanitation practices are sound, and have never had the slightest infection. I have full fermentation temperature control, so that is not a factor either.
The only thing that makes any sense to me is that adding CO2 (carbonic acid with a pH around 4 at a pressure of 12 psi) to the beer is activating the buffer in 5.2 and producing this flavor.
If anyone has had this experience or can lend any insight, it would be greatly appreciated. No more shits and giggles for me.
