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. The fluid dynamics of home chocolate fountains are particularly problematic (it is a so-called non Newtonian fluid), since the gravitational forces are much lower than the viscous forces; this means that small chocolate fountains need a very high proportion of vegetable oil. There is a trade-off between looks and taste: if perfect smooth flow may be sacrificed, it's possible to use non-oily chocolate. A cheaper alternative to couverture chocolate is chocolate-flavored syrup, also called "chocolate coating". Chocolate coating is already in liquid form and costs much less than couverture chocolate, though some connoisseurs prefer gourmet Belgian couverture despite the added expense. Another alternative is to use dark chocolate, such as 70% cocoa chocolate. This contains much less sugar, so it isn't so sticky; a small quantity of hot water may be added to thin it further. Increasing popularity Originally, the market was entirely commercial, with chocolate fountains costing a large amount of money and requiring significant upkeep. The popularity of chocolate fountains grew to a point of demand at a consumer retail level as people who had seen commercial models at catered events inquired about purchasing their own fountains. Then, at the end of 2004, the Hellmann Group began marketing the Nostalgia Chocolate Fountain for personal use. This expansion into the retail market caused the demand to peak drastically. As a result, the catering industry saw more requests for chocolate fountains at events. Flavoring oils such as mint, orange, and cappuccino were developed to give the chocolate extra taste. Caterers began adding food coloring to white chocolate to make it coincide with special holidays or events. Caterers and home users created special recipes for a variety of fondues that would flow well in a fountain; some of the more