This recipe worked perfect for me, a very controlled method, outcome is you know what % solution you are extracting.Dr. Marla Spivak from the Univ of Minn. was at the fall Missouri State Beekeeper's meeting and talked quite a bit about propolis. Here is a link to a page on making tincture from their web site. http://www.tc.umn.edu/~reute001/htm-files/Propolis%20extract.html
I made some of the 30% solution with Everclear last fall.