I noticed my bottle caps are turning black on the side exposed to the beer. The black discoloration is under the plastic coating on the caps ( I scraped the plastic off with a knife). The beer was bottled end of november 2021. Not terribly concerned as its on other side of plastic not touching beer. Just seems weird. The caps are from an overrun of caps from either phillies or pirates. Caps are like 5 years old…got a gazillion of em cause they were cheap. I bottle aged chimay blue and red clones for over a year (about 4 years ago) and never saw this before.
Anyone seen this happen?