the point that it has a spreadable consistency. Let cool. Puree. If you are canning, reheat the puree and boil a bunch of jars. Spoon the hot plum butter into the hot jars, filling to about 1/3 inch from the top. Put Saran Wrap on top and seal with a rubber band (Al's mom's canning trick). Once the Saran Wrap has a concave dent in it the jars are sealed.