The ideal storage temperature for chocolate is between 12°C to 18°C with a humidity level no higher than 65%. Chocolate suffers from temperature fluctuations. For example, cold temperatures harden the chocolate on the inside, and the action of moisture causes an opaque, translucent coating to appear on the surface. Heat, on the other hand, melts the cocoa butter content, which, once set, crystallizes causing a whitish layer to appear on the chocolate surface (tempering). Other alterations in the texture and appearance of chocolate may be due to light exposure or storage alongside strong-smelling food. Exposure to light causes the cocoa butter content to deteriorate and it may absorb flavors and odors of other foods nearby. As a general rule, chocolate and chocolate products should be kept in their original packing and stored in a cool, dry place.