Eventualy your sourpuss will start to sugar. This means that the liquids are
evaporating and the sugars are coming out of solution. I don't know how long
this will take, but it will happen. Also if it sits for too long, it will
start to get a flavor that is a bit dusty. if you use this liqour fairly
frequently you should be OK, but if it is sitting for months and not being
used at all, you may want to reconsider purchasing it. Refridgerating
somethng like this may help extend it's life, but not by much because of the
very high sugar content.
Good Luck!