Over time, dried vanilla beans can develop natural vanillin crystals that form what looks like a white frosted coating on the bean. These white crystals are a sign that the vanilla beans are high in vanillin and are excellent in quality. Don't worry about cleaning the bean since these crystals are quite edible and very flavorful and do not need to be removed prior to use. To make certain the crystals are not mold or mildew a simple test will confirm the presence of vanillin. Place the beans into sunlight. The crystals should create multiple colors. If the white coating is mildew the beans will have a dull and flat appearance in sunlight. Mildewed beans should be discarded, since they may give an off taste to your finished product if used.