I just noticed an interesting buildup in my stainless conical fermenter.
I thought I had been keeping my fermenter perfectly clean for over a decade, but I noticed prior to my last brew that it had a very light tint on the interior surface. Since I spent days polishing the interior of the fermenter when I bought it, I have always avoided hard scrubbing with scrubby pads. But I have always been thorough in scrubbing the surface with either my hand, thumbnail, or sponge to remove any sort of trub, yeast, or other deposits. It always looked
clean and shiny.
So with some 60 or 70 batches fermented in that vessel, I happened to notice that there was a tint to the stainless surface. I used my thumbnail and was able to scrape it off...grudgingly. It was some sort of a transparent, tan coating that I guess could be termed "varnish".
I still didn't want to use a scrubby since that is known to create micro scratches in metal surfaces. So I tried a warm PBW soak. That helped a bit, but I'm pretty sure that it's ~110F temperature was not enough to really activate the solution. I then hooked up my RIMS and circulated the solution at 160F and it further loosened the layer. I could get more off with my nails. Ultimately, I pulled out a white scrubby and lightly scrubbed the surfaces to get all the varnish off.
It's clean now, but I have to wonder if critters may have been lurking in that microscopic varnish layer that may not have been knocked out with sanitizer? Fortunately, my prior beers have been good, but that question has to remain.
While this event hasn't diminished my avoidance of harsh scrubbing with a scrubby since its obvious to me that the micro scratches will eventually become filled with that varnish, I wonder if anyone else has experienced this?
The good news for me now is that I know that I need to perform a substantial PBW cleaning in order to remove something I can't even see, on a frequency a little greater than once in 60+ brews.