A friend of mine gave me some sourdough starter in a sealed jam jar. I can't remember how long I stored it before trying to use it, but it wasn't more than a week. I pulled the jar out and loosened the top just a little and *BAM!* Th entire thing just exploded sourdough starter all over the kitchen. It was in the kitchen drawers, all over the counters and oven! After the initial bang my boyfriend came into the kitchen to see what was going on and you should have seen the look on his face when he saw me standing there with a jar in my hand, sourdough starter ALL OVER THE PLACE and a slightly dazed look on my face!
Did I forget to mention the slightly *yeasty* smell that lingered in the kitchen? :D
So please remember the moral of this story....never store sourdough starter in a tightly sealed container.