By Gerald Van Hecke ’61, professor of chemistry

At room temperature chocolate is an immiscible mixture of three solids: crystalline sugar, cocoa powder, and cocoa butter crystal V. Melted chocolate is a misnomer for only the cocoa butter actually melts and as a liquid serves as a “solvent” for the emulsion of the sugar and cocoa powder. The emulsion of sugar and cocoa powder provides the sweet “chocolate” taste.

Cocoa butter is a triester of glycerol formed with fatty acids the most common of which are palmitic, stearic and oleic acid. Cocoa butter exhibits a rich polymorphism in the solid state characterized by the existence of six crystalline phases whose phase transition temperatures [melting points] are given as:

crystal I 17ºC  
crystal II 23ºC 
crystal III 25ºC 
crystal IV 27ºC 
crystal V 33ºC 
crystal VI 37ºC  liquid

Crystal V gives chocolate its desirable properties of easy melting in the mouth and snap when chewing. In making chocolate, the melted chocolate liquid is cooled in a process known as tempering.

CHALLENGE:
Explain the process of tempering in terms of the phase behavior of cocoa butter.

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