Why does cocoa butter melt in the mouth but stay solid at room temperature?

Cocoa butter remains solid at room temperature and melts in the mouth due to its unique fatty acid composition and polymorphism.

The fat consists of triacylglycerols that form specific crystal structures. Because 70 percent of these molecules are solid at room temperature (25 °C or 77 °F), cocoa butter maintains a stable, firm shape.1

However, these crystals have a melting point ranging between 27 and 35 °C (about 81 to 95 °F). Since this range is below human body temperature, the fat dissolves rapidly upon contact with the mouth, providing the characteristic creamy texture associated with chocolate.1