Yesterday I brewed an oatmeal stout using extract and seeping grains. I used wyeast irish ale yeast. I looked at my carboy this morning, and about 8 inches up from the bottom is a cream colored ring, about a 1/2 inch wide. I’m not terribly worried about this, as I am assiduous about my sanitation and cleaning, but was curious as to what it is. Anyone ever encounter this? Thanks!
I’ve noticed that I sometimes get sediment clinging to the sides in a ring that sounds like what you’re describing. The ring only happens in some of my carboys even when I split 10 gallons of the same batch between two. I’m assuming the inside surface is not completely smooth and there is a slight ledge or slope where sediment can get stuck. It has never seemed to affect a batch, but I usually use different yeasts when I split a batch.
Anyway, does it sound like the same thing, or something else?
Well, it happens to fall in between two ridges, and I’ve also noticed that below the ring, the fermenting wort is considerably darker than above it. I have used this carboy for 4 other brews, (I have three glass carboys) without seeing this occur. I’m sure it will be fine, as it is already bubbling merrily away.
If it’s noticeably darker on the bottom, it might be that it is not properly mixed - did you do a full boil, or did you top up with water and give it a shake? It might be worth it to give it a good shake to mix the layers and disturb that ring which should fall to the bottom. Just a thought based on what I’m picturing.
I did a full 60 minute boil with 2 1/2 gallons, and after chilling, I topped it off. I shook it vigorously for 2-3 minutes to aerate. After pitching the yeast, I shook it briefly (but gently this time) again to distribute the yeast. I will shake it again and check on it in a while. Thanks, Tom for your time and advice!
Yeah, ok, so it sounds like it’s not mixed well. By full boil I meant full volume, sorry for not being clear. Don’t trust any hydrometer readings you took :) Next time you might add a gallon or so of water to the carboy first , add your wort, and then shake a lot to mix it and aerate it. Then top it up to your final volume and mix some more. Or use a mix stir, they are relatively inexpensive if you already have a drill to attach it to.
But above all at this point, RBWHAHB, it will be fine. 
Ok, just checked on it. After shaking it again, the sediment ring disappeared, and the color evened out. But now after 2 hours, it has separated out into lighter/darker again. It’s not a gradual changs, but a distinct line. I’m not worried, it is visibily fermenting, but I guess I don’t understand why it separates.
I use a mix-stir rod with a cordless drill to not only aerate the wort but also to blend in any water additions as well. It will do the trick for sure.