[narcout]

Does anyone know if this is beerstone or just stubborn crud?  Neither oxyclean nor PBW will remove it, though I can scratch it off with my fingernail.

Secondary question, is it ok to use a blue, non-scratch scrubby on the inside of a stainless fermentor?  I use them all the time on my brewpots without issue, so it seems like it should be ok.  A good scrub with one of those would definitely take this stuff off.  Otherwise, I guess I'll try some sort of acidic cleaner.

Thanks.

[beersk]

Interesting. I ferment in kegs, I hope there's none of this kind of crap in there I can't see. Are you noticing any subtle off flavors in your beers? I'd guess that whatever that crud is won't affect your beer, but I'd be bothered that it was there as well.
Barkeepers friend would take it off...

[theDarkSide]

+1 to Barkeepers Friend.  With that stuff, you can clean the stainless with a sponge. 

The wife loves it too because I can make the kitchen sink look like new with it.

[WDE97]

+1 to Barkeepers Friend. I use it routinely with one of those blue non-scratch sponges to clean all of my stainless equipment. Works great!

[narcout]

No doubt BKF would get rid of this stuff quite easily.  I've just always been wary of using it on the inside of my fermentors (I do go to town with that stuff on my kettles though, makes them look brand new).

I ferment in kegs, I hope there's none of this kind of crap in there I can't see. Are you noticing any subtle off flavors in your beers?

I have seen it in my corny keg fermentors.  If it's there, you should be able to see it with a flashlight.  It also has kind of a rough texture that is pretty noticeable. 

No, I haven't experienced any off flavors, and none have been mentioned by any judges.

[hopfenundmalz]

My conical was looking pretty "brown" I gave it a long soak with hot water and PBW, really shiny now.
 
Acid takes off beerstone, so it was not beerstone, just built up organics.

[HoosierBrew]

Another +1 to BKF plus a blue sponge on the kettle.

[archstanton]

Yes, that is beerstone.
No, it will not come off by scrubbing it, even with the green sponge.
Yes, it will take an acid based cleaner to get it off. BKF works for me.
No, it still will not come off easy with BKF.

It is really attached and begins to form layer after layer, get what you can off with your fingernail, then depending on how long(how many layers have formed) you can start to remove them with BKF. It may take several applications. 

You can wipe it with a wet towel and it appears to be gone until it dries and voila -still there.
Feeling for any "rough" surface on your stainless will locate this stuff for you. It is like chiseling away at stone.

[graymoment]

Yes, it is beer stone. PBW and other cleaners that work on the alkaline spectrum will do a good job with organic materials, but you will want an acid based cleaner for the inorganic stuff, such as beer stone. The added benefit is that you can passivate at the same time.