Each time you are done using the gourd, it is recommended that you discard the used yerba mate in order to allow the gourd to dry and prevent too much mold from developing. Wood gourds hardly ever develop the moisture mold. Traditional gourds, however, if allowed to remain moist for too long, will develop a natural mold. Often this happens during the curing process. Do not be alarmed, the gourd can be easily cleaned. NEVER USE SOAP. NEVER USE DETERGENT . The majority of yerba mate drinkers merely use boiling water to destroy the mold. The native yerba mate drinkers point out that the remains will discolor the gourd, but not make the gourd unusable. Indeed, some Latin Americans suggest that some of the benefits of yerba mate (specifically the reparation of the heart muscle) may be imparted by the unique mold that the yerba mate and the gourd combine to create.