I had used a 5 gallon bourbon barrel to age 2 beers in which both came out great. After draining the 2nd beer, I didn't have another one ready to go so I filled it with 5 gallons of water with potassium metabisulfate. Unfortunately I was not able to brew for a couple of months and let the barrel sit. I drained it today and it looks like it began growing mold. Before I trash the barrel I wanted to get some confirmation of what I am thinking. The picture below is what I emptied out into my sink. Can anyone confirm if what is floating in the liquid is mold, and if so, is this barrel likely shot?