It's five weeks today since I started vaping, and I've gathered quite a collection of opened, tried-once-and-didn't-like bottles. I'm keeping them in a cupboard at the moment as they may improve with steeping. But is there a point in time by which they should be thrown out? Any pointers from more experienced vapers would be welcome.
I think a good rule of thumb would be:
~Uncapped (exposed to air): Don't keep open longer than one month, I've had a banana juice (that was amazing) turn to cheese, it was pretty gnarly...I've never had a juice change flavor that bad on me. It tasted stale (I vape a tiny bit after shaking to see if it was maybe the bottle), and just...plain wrong on so many levels. It was literally strawberry banana smoothy, with a dash of lovely nacho cheese *gag*. It may have been the dairy flavoring, but the banana seemed to be the culprit. No 30ml bottle of juice (no matter how much ethyl alcohol is in it) will need to steep open for a month, heck I'd say 2 weeks is pushing it honestly.
~Capped: I'd say 6 months, I have an "in vino veritas" Virgin Vapor bottle (which is aqua di gio wine), which is too high to drip, thus it's been sitting in my droor (with the occasional shake and smell), and just last week, around the 7 month mark, it tasted a little condensed. It wasn't bad, it was just like that beer/soda you drank the next morning, flat, and slightly "syrupy" tasting. It was just a little stronger and thicker, so I rinsed the bottle out and threw it in my juice graveyard backpack (it's almost full!

).
I'd treat juices the same way you treat...maple syrup (may be a weird example), which almost doesn't go bad ever when sealed, however you'll get that thick "skin" sometimes on a good multi-month old bottle, just toss it if it's been months, and doesn't smell right. After that banana/dairy juice, I really think in some cases, it can be bad for you.
Hope this helps!
