Home Distiller

I have quite a few very ripe sweet plums in the orchard. Tthey are so juicy you almost have to drink them instead of eating! My plan was to ferment them with the object of distilling Slivovice in the traditional way as much as possible. I followed the excellent and charming youtube video on the subject by picking up the very ripe plums and periodically adding more to my container. At first they were bubbling and fizzing all over the place. Now the bubbling has stopped and the mix smells more like vinegar. What did I do wrong? Is there any way to salvage the mash by adding new plums and altering the fermenting in some way? Or should I just throw it out and start over with new plums?