i've had a few "rings around the bottle" mostly mine are consistant with stouts and porters. and no big - they have all turned out great.
this is another porter. and this is more like a film than anything. - i have sampled one or two - and though green and young - there are no horrible tastes in fact it seems to show promise in the taste dept. so i'm pretty darn sure it's not an infection.
my sanatation process has been the same - everything seems to have been followed with due diligence.
would this scare you?