I brewed up a gruit 10 months ago by loosely following the recipe in sacred and herbal healing beers. I ended up "dry herbing" in the 3 gallon corny by adding a stainless steel herb ball filled with dried yarrow. At first tasting (march) it was too strong of an herbal flavor, so I stuck it in the corner and forgot about it until today when I needed a 3 gallon corny. I figured it was a dumper but tasted it and it was really interesting, it had picked up a rather strong but pleasant sour taste. Did the yarrow sour it? Would it still be safe to drink the rest even though I had the herb ball in it the whole time?