Vegetable oil
Melted chocolate is very temperamental, so rich couverture chocolate, which is high in cocoa butter, is commonly used to ensure consistent flow. If the cocoa butter content of the chocolate is too low, an additive must be mixed in to decrease viscosity. (Vegetable oil is most commonly used to do this.) But even couverture chocolate—unless specifically designed for fountains—often still requires an additive to make it flow smoothly. Because of this, it is highly recommended that chocolate formulated specifically for fountains be used to avoid the need for the addition of vegetable oil, as the oil gives a slimy, gritty taste and texture to the chocolate. Few chocolate fountains are capable of melting chocolate directly in the basin, so chocolate is typically melted in a microwave or double boiler before pouring it into the fountain.