Bottle "Frost" - What is it?

[Grizzlybrew]

So,

I did a quick search and gave up... came to my friends here.

I decided to pour out some beers last night that have been laying around for 6-12 months to reuse the bottles. I thoroughly rinsed the bottles, capping with my thumb and shaking with hot water, and then set them up on the tree.

This afternoon, I started to move the bottles to temp storage and noticed a "frost" on some of the bottles (see below) You can see it exists only where the beer touched the glass. I think most of these were from a dark belgian I did a year ago.

What is this exactly? I brushed/cleaned a few bottles and I'm sure some B-Brite soak would take care of it, but what is it?

 

[Coastarine]

It took me a second to realize that you were holding an empty bottle. It looks like the beer took the pigment out of the glass! Wierd.

 

[conpewter]

beerstone?

 

[DavidSteel]

Looks as if there was something in there that cleaned/polished the glass and maybe even took some colour off. You bottle an IIPA in there ?

 

[GNBrews]

My bet is with conpewter, looks like mineral deposits. Do you have any Star San around? That, or vinegar should remove it.

 

[Oly]

I've seen exactly the same thing on some of my bottles. Can't figure it out. It cleans up fine with oxyclean/brush, but makes you wonder WTF. It was on a string of consecutive batches last year and I haven't seen it since. One of the batches might have been infected, but I know the other batches were not. Bottles were very old, maybe beerstone? I've started kegging since then so I don't worry about it too much anymore but I wish I knew what it was.

 

[GNBrews]

The real easy way to tell if it's beerstone is to put a bit of diluted muriatic acid in the bottle and see if it fizzes on contact. Vinegar fizzes too, but it takes a while to react.