Melting of chocolate

Chocolate is an emulsion of cocoa butter fat particles in the liquid phase of the chocolate, either milk or water. Therefore, chocolate’s melting ability is due to the fat content of chocolate, provided by the fundamental ingredient of cocoa butter. It is the cocoa butter fat particles' crystalline structure and relative distance apart that determines the consistency and state of the chocolate.

There are six different crystalline forms of the cocoa butter fat and their unique arrangements lead to different textural and physical properties such as melting point and appearance.

Polymorph	conditions to make the polymorph	melting point (°C)
Form I	cooling molten chocolate rapidly	17.3
Form II	Cooling molten chocolate at 2°C	23.3
Form III	Solidifying the molten chocoate at 5-10°C or storing form II at 5-10°C	25.5
Form IV	Solidifying the molten chocoate at 16-21°C or storing form III at 16-21°C	27.3
Form V	Solidifying the molten chocolate while stirring using special process called tempering	33.8
Form VI	Storing form V for 4 months at room temperature	36.3

As a solid piece of chocolate, the cocoa butter fat particles are in a crystalline rigid structure that gives the chocolate its solid appearance. Once heated, the crystals of the polymorphic cocoa butter will be able to break apart from the rigid structure and allow the chocolate to obtain a more fluid consistency as the temperature increases. This is known as the melting process. When the heat is removed, the cocoa butter crystals will become rigid again and come closer together, allowing the chocolate to solidify.

This temperature in which the crystals obtain enough energy to break apart from their rigid conformation would depend on the milk fat content in the chocolate and the shape of the fat molecules as well as the form of the cocoa butter fat. Chocolate with a higher fat content will melt at a lower temperature.