On the subject of enzymatic cleaning of shells I suspect any papain
containing fruit juice would soon dissolve any proteinaceous material.  We
use pineapple juice to break down intestinal obstructions in rabbits. Papaya
juice would also work.  Adolph's meat tenderizer in solution would also work.
 Obviously none of the above would have any action on the concretions
covering the shell.
I would be interested to know if anyone has tried any of the above.

Dr Jim

(Please no coments on using the Adolph's on the rabbits,drinking the juice
and using chlorox on the shells)