I've opened a new tin of gin and tonic from samuel gawith and noticed a weird "ring" of darker snuff surrounding the edge of the tin. It's certainly not rust - tin looks brand new after removing darker snuff from the edges. It seems like it's just much more moist. Could that be a first sign of mildewing? I've asked the same question on a facebook group and someone said that this could be caused by condensation, which seems reasonable.