What is that stuff?

Yesterday I chilled some bottles of my second brew down so I could drink them tonight. When I put them in the fridge, I noticed that one of them had white stuff inside the glass where the head space area is. When we drank them tonight, I made sure I got that one because, I wanted to see what it tasted like. They were flip tops and mine made a fft sound when I opened it but it didn't make the fwop sound like my wife's did. I poured it and it made a decent head. When I tasted it, it had a sourness to it and not as much carbonation as usual. It wasn't horrid but it wasn't good. I tasted my wife's and it was excellent. It also didn't seem to have the alcohol kick that I feel when I drink one of my brews for the first time in the day.
I figure it was one of two things.
Contaminated bottle or bad seal.
The gasket was brand new.
I'd just like to get to the bottom of it to try and avoid it in the future.
Any ideas?

If it was just this bottle and had a sourness it is most likely an infection of some sort. Could have been either the bottle or gasket. Did you sanitize the new gasket?

Sour usually indicates infection - especially if its just restricted to a few bottles. I've had bottles that didn't get as clean as they should have and had a single bottle or too end up infected while the rest of the batch was fine.

If you're seeing a ring around the top of the beer where the beer meets headspace thats generally a sign of infection. Hard to tell what is going on there since you poured it out. That foamy white stuff looks like some yeast in suspension with some foamy beer but it could very well be something worse. I usually find flavor to be a better indicator than appearance unless something looks REALLY bad.

I sanitized the gasket. I usually sanitize them in a bowl of star san along with the caps and then strain them in a sanitized collander.
The way it looks in the pic is the way it looked before I poured it. It was only in the head space. Looks kind of like lacing but, it's sort of a milky substance on your fingers.

Sounds like an infection to me. If its limited to one bottle I wouldn't stress about it. Maybe some nasty bacteria rode a piece of dust right into the bottle as you were filling.

Also, if you don't have one a bottle rinser provides some good peace of mind. I always rinse my bottle with one of the jet carboy/bottle washers with hot water until the glass is uncomfortably hot in my hand and then move it to star san. If theres chunks of stuff in there, however small its possible that the starsan couldn't get to all the bacteria and some was left alive. I wouldn't worry unless you see this cropping up in a signifcant portion of the batch.

I soaked these bottles in clorox brand oxyclean. I got real oxyclean recently and couldn't believe the difference in how well it cleaned. This might have something to do with it.