I had another jar going (these are re-used jelly jars) but it formed a hairy mold on top. I fed that back to our municipal water. I don't want to rinse the raisins since I feel I may wash away yeast. But it looks like there are other things growing on raisins that I don't know about.
The raisins that formed mold were Newman's Own Organic. The raisins that gave good yeast growth were Trader Joe's Organic Thompson.