I tried harvesting from a corked bottle a few months ago. My advice is to start with a really small starter and build it up. I don't think there's not much at all alive in there. After a month+ of decanting/adding fresh wort every week or so, I ended up getting a nice layer of of stuff going on the bottom of the flask. Liquid tasted slightly sour but mostly funky. I have it sitting in my fridge still, but will probably try adding it to a small beer sometime in the future to see what it does.