I made some stem tea a couple months ago and stored it in some old soda bottles. A couple weeks ago, a friend opened it, and an unusual amount of carbonation was released. When it finally settled, my friend took a drink and said it tasted kinda like beer, so I took a sip. He was right. It took only a little bit of it to **** him up too, which was surprising. Does anyone have an idea how it could have carbonated and changed the flavor to beer? Is this fermentation?