According to What's Cooking America, chocolate melts because its cocoa butter crystals liquefy when heated. The melting point of a given chocolate type is inversely proportionate to its cocoa butter content. White chocolate melts at a low temperature because it contains more cocoa butter than other types of chocolate. Dark chocolate, which contains the smallest percentage of cocoa butter, has a higher melting point.
Commercial chocolate has a shiny surface and snappy texture because manufacturers use a carefully controlled melting process to cultivate stable, evenly spaced fat crystals. This procedure is called tempering. Chocolate that is melted and cooled without a second tempering has a dull appearance and mushy texture. Untempered chocolate is often to blame for overflowing candy moulds, because tempered chocolate shrinks slightly as it cools and home candy recipes assume the use of tempered chocolate.
According to candy and chocolate expert Elizabeth LaBau, home tempering is simple and easy, but requires a quality candy thermometer and the baker's undivided attention. A spoonful of properly tempered chocolate daubed on a plate dries quickly and has a shiny finish. Without proper tempering, melted chocolate solidifies slowly and has a sandy, grainy texture. Its surface is dull and uneven. Homemade confections made with tempered chocolate have a firm texture and a glossy, professional appearance. Over the next few days, the shine and texture grow more pronounced.