A slow firm twist usually does it but be warned that the odd one will not come out of the bowl and split, probably because the part of the shank resting on the bottom of the inner bowl is to well glued. What I've done to all my MM's is to drill out the bottom of the bowl, including the part of the shank that is glued too the bowl's interior bottom. Then the stem easilt twists out. I insert the right sized hardwood dowel, adjusting where the hardwood meets the airway, and gluing it with Elmers glue and let it dry. Then I saw off the dowel, reglue the stem to the bowl, and voila, a MM with a hardwood bowl bottom. It's a lot less trouble than it sounds like.