This happened to us before I got into homebrewing. A flawed carton of juice swelled up in the cupboard. Upon having a little sip I confirmed that 'yuk, it tastes a bit like wine' and being ignorant we threw it way!!
Now that I understand fermentation I'd probably have drunk a bit more of it to see what it was like!
It's a bit like when (apparently) during Prohibition they sold grape juice with labels saying "warning, do not store at room temperature for 28 days or this will turn into wine"