I've done a pretty decent batch of vanilla bean extract using pure PG as the solvent. Using whole, dried vanilla beans, I used a razor blade to place vertical slits along the length of about 20 beans and soaked them for about 2 weeks in a mason jar filled with PG, shaking the jar 2-3 times a day. It's still a work in progress for me to figure out the optimum ratio of beans/PG/soak-time, but my last batch worked out well for vanilla flavoring. I stayed away from adding water to the PG as a solvent out of concern for bacterial growth during the soaking process. From my research, PG has inherent anti-bacterial and anti-fungal properties, so I used straight PG and had no visual indications of fungus or mold growth over the 2 week extract soak. A Google search will produce a good number of links to folks who do extracts for a variety of purposes. You may wish to check some of those resources for hints and suggestions for safe and appropriate extract methods.