Maybe I’m wrong here but I would think that the bean would need to be “opened” to get the flavor to extract. You don’t put straight beans in when you are making coffee. The outer shell protects the bean and keeps its freshness. It’s only after you “open” it by grinding that you release the flavors. But that also opens up a whole new issue of having to strain the grounds out. Shouldn’t be too difficult in PG but if it wa in VG then that could be a real pain!
As a test to see what I mean, put a bean in your mouth and test for flavor, then bite down on that bean and see the difference. Kinda of like a chocolate covered espresso bean. After you suck off the chocolate not much coffee flavor but after you bite into it, boom, huge flavor.
Here would be my method. I would take a bean or two and break it up with a spoon so there would be bigger pieces. Then put that in some PG, heat it for a bit in some hot tap water in a UC. Then strain that through a coffee filter.
As for the bitterness, different beans will play a part here. Some are more acidic than others just like in a brewed cup of coffee.