Making Yeast From Fruit

I am currently trying to start my own yeast from just raisins and spring water. It seems to be working but I have no idea how much to use or how aggressive this strain will be. My current setup is a box of raisins in enough spring water to submerge them. I have this mixture in a 2 liter bottle that has a homemade cap with a valve stem in the middle that I have used to carbonate my concoctions. (I will let you in on the carbonation hows and whys if you're interested) As the raisins ferment they create pressure so I press my thumbnail down on the valve stem to release the pressure once or twice a day. It took a couple days for anything to happen but now, after about 5 days or so, the raisins have a sort of "fizz" to them and I am waiting for that to stop and my mixture to lay inactive to let me know that it is complete. Like I said, this is an experiment so I am kinda shooting from the hip on this one. I have been able to find very few resources on starting a natural yeast strain so I gotta put on my scientific lab coat and do some experimenting. I will let you know how it turns out as my first experiment after the fizzing stops (if it does) is to separate it into 4 different containers and I am going to try to add one of the four to straight apple juice to make a sort of hard cider. Stay tuned and I will let ya know how it goes.