I have some metal containers I put a 150 mesh bags in, fill the bags with trim, put it all in the freezer. After its frozen I put the containers in a Harbor Freight vibrator and I get a good yield of keif and generally refreeze and run them again. To test the coin theory I threw 2 quarters in each bag and ran it again. 3rd run I got nada. Funny though I use credit cards so much I had to search all over for 6 quarters