Acetobacter is the bacteria that makes vinegar, a main ingredient in pickles. If you like it, drink it relatively fast because eventually you will have malt vinegar. If the beer hasn’t been fermented yet, the sour flavor can come from soaking your grain over a couple of days at room temp before mashing. Also, I’ve had a very light taste of sourness from grain that was at some point not properly handled, but it wasn’t pronounced at all. I only knew it was from the grain because I tasted the grain before mashing in.