A unique capability of Shuckle is the ability to store berries in its shell.  For any other pokemon, long term storage of berries would result in eventual decompostion and wasted food.  Shuckle, however, turns berries into flavorful juices over time.  No matter how long it stores food, it will never be inedible.  Juices, jams, alcohol, and even medicines are within the scope of this pokemon's capabilities, depending on how long the recipient wishes to wait for the desired product.

     The secret seems to lie in the pokemon's skin.  Shuckle secretes a fluid that ultimately aids in rapid breakdown of the stored fruit, simultaneously enhancing its' shelf-life.  Furthermore, this same fluid seems to retard the growth of any foreign matter inside the shell.  The environment is unsuitable for bacteria or any manner of fungus to develop.

The label of Shuckle as the "Mold Pokemon" is clearly a misnomer.