Leftover Particulate in carboy

[Twisted Brick]

In preparation to rack a finished bourbon mash to secondaries, I found a dried (and hard) mess I left in one of my carboys. It appears to be a particulate that I didn't catch when rinsing the prior batch out. Strange thing is it is tinted blue. I don't remember if this carboy housed the clear portion of the mash or the cloudy, opaque portion that came off the second half of my keggle.

Anybody seen this before? Recommendations to remove? My first inclinations are citric acid or PBW, but thought I'd ask first.

Thanks,

TB

[fizzix]

I'm wondering if any copper in your process needs cleaning.
The copper worm I once had would sulfate if distillate was left in too long. Then pretty blue would come out on next run, suspend in the mix, and some would adhere to the glass jar walls.
A good hot water run through the worm would clean it out. (A good scrub would've been proper, but not possible in a 25' worm.)

[Twisted Brick]

I'm wondering if any copper in your process needs cleaning.

Well, I was able to rule out copper since the only thing I was storing in the carboys was freshly squeezed corn mash. I did have a tin foil cap on top of it, which concerned me a bit. Anyway, I did a hot soak with citric acid overnight which loosened the grit, and turned it white. This morning it manually scrubbed out easily, and I gotta say, citric acid made the glass look new. Gonna clean with it every batch from now on.

Thanks for the feedback, fizz.