Apparantly, German Riesling is never casked, but bottle matured and can be left for up to 30 years.
Mine has been casked for 1 month and is much improved but is now light yellow, presumably due to oxidising, so I should continue to monitor it.
As yet, I don't have 60 spare bottles, but I'm now inclined to get lots more, because, apparantly, even plastic containers breathe oxygen.