Grey debris in used oak barrel

[kgranger]

Currently swelling and reconditioning two dry, used whiskey barrels to prep for some beer aging. I’ve rinsed and dumped several times, and looked on the inside as best I could via the bung hole. No visible mold or anything, just a nice looking char. After I filled one last time to ensure it fully sealed the gaps, I noticed grey bubbles and particles in solution. My guess was that it is just debris from the grey ash from charring, but I wanted to make sure before assuming. Does this look like anything else? This doesn’t rinse out fully, after many rinses. It smells like oak and whiskey, like the rest of the barrel, no aroma of mildew or anything funky.
FYI the beers going in here will be intentionally soured, so I am not worried about residual microbes from previous batches. I just don’t want any unwanted bacteria or mold.

 

[Dr_Jeff]

I agree, it looks like cahr debris to me.

I took my barrels and rubbed them all over on the outside with gulf wax, then took a heat gun and melted the wax into the pores of the wood to slow down evaporation.

 

[kgranger]

Update on the barrels, hoping for some advice. I cleaned them out as best as I could with boiling water, drained and left dry for a couple weeks. I filled them up with a storage solution of potassium metabisulfite and citric acid mixed in water. After a few days I am getting bluish grey mold on both around the bung hole. Now I am very aware these barrels had been infected with wild bugs with their previous owner, and I was looking forward to this as I intend to age sours. Does this mold look concerning, or can infected barrels have mold like this on the surface? If it may add funkiness, I'm down for it. If this looks really bad and could completely spoil the beer, maybe not. I'll probably have to just put a batch in it and find out, but if this looks bad just from a photo alone, that's a sign that I shouldn't bother.

 

[Dr_Jeff]

At this point, it's just a guess.

Are you willing to risk the investment of time, work, and beer/ingredients on it?
If so, go for it.

I'd pour some bleach on it and scrub it with a brush, since you are going to dump the storage solution anyway.

You might consider, buying several packages of the "bugs" that you want in it, add them when you fill the barrel and be prepared to fill it up entirely when you do fill it, so that your know bugs have a good start. Any beer residue can mold, if left out. Pour an inch or so in a glass and leave it for several days and you'll see.

Sand paper might get it off.

Good luck with it.

Owning a barrel can be both a blessing and a curse.