I keep mine in the fridge and have it whenever I remember. Sometimes there are bubbles in the surface but I don't notice a difference in the taste and I'm still alive. So I suppose it is alright
Thanks guguess for the info!
From the little that I know, if it's just alcohol fermentation, even if there is vinegar fermentation, it should not be a problem. Vinegar with live culture may even be beneficial for our health, and vinegar itself is used as a preservative, like in pickled products, so it will last a really long time, just won't taste very nice.
The sour taste could either be due to carbonation of the co2, or more unlikely due to vinegar forming. I suppose the only time you need to worry is when there is mold growing in the molasses, like when you start seeing colourful mold growing, or some fuzz on your molasses, then that's definitely time to throw it out. When in doubt throw it out, or I would be glad to take it off your hands.