Yeast raft or infection? (in bottle)

I had finished up my brew about a month ago and bottled everything up. I was away for about 3 weeks for work, came back and had a beer. It tasted fine, nothing was growing in it or anything. I was away for work for another 10 days and just returned. i looked at the top of my beer bottles and saw these things forming in almost every bottle. my question is, "is this a yeast raft somehow forming 4 weeks after being bottled? or some infection that is rearing its ugly head just now 4 weeks after bottling?" I have read many threads about yeast rafts but haven’t found any pertaining to them forming well after bottling so any advice would be greatly appreciated. Thanks All.

Hard to say.

Could be, could be mold which wouldn't hurt you and probably won't hurt the beer.

Could be crud you failed to wash out of your bottles rising to the top.

How does it taste?

Looks like a raft to me. Taste it and you will be able to do it. Do the other bottles look like that?

I have done a few batches of beer before and never had this problem. Out of my whole batch I’d say 75% have it. All bottles were washed, visually inspected, and left in sanitizer solution for over an hour (caps also). It just seems odd for something to start to show up 4 weeks after bottling. Or is that something that is not uncommon of yeast rafts and or molds?

also, it taste like beer still. i just don't want to be sharing moldy or contaminated beer with friends.

Well, most top-forming infections are oxygen-loving bacteria. There is generally a little oxygen in the headspace of a bottle, but the yeast typically eat it when you are bottle conditioning.

So, an oxygen-dependent infection in a bottle conditioned beer is unlikely. Way less likely than a yeast raft.

Invert the bottles a couple times and see if it falls back out?

This morning I took a hand full of them and inverted a few times and the stuff disappeared. I leave again for work today and will be back in about 2 weeks to check and see what happens in the long run.

so i came back a few days ago and checked out the beer. it must have been yeast rafts, cause nothing was there this time and it tasted fine. so all is well. thanks for the help!