The Structure of Stuff is Sweet!

Chocolate is a treat that many of us enjoy on a regular basis.  It is best consumed as a solid and that means crystals!  Did you know that it is actually quite a complicated process to make this in a way in which we enjoy?  Can you imagine chocolate that didn't melt in your mouth in that creamy smooth way?  During the chocolate making process, chocolatiers use a process called tempering.  This is a heating and cooling process involving stirring and if they don't get it right, the chocolate isn't good!  Likewise, if you leave chocolate for a long time or it melts and resolidifies, often you see a white coating on the surface and when you taste it, it isn't quite right, the texture is gritty and horrible.  Its called blooming.  This is all because of the way that cocoa butter molecules arrange themselves in the solid crystal.  There are, in fact, six ways in which cocoa butter molecules can arrange themselves into a solid; same molecule, no Chemistry, just the crystal!  This is called polymorphism.  Only one of these arrangements gives good chocolate that melts in your mouth.  Unfortunately, there is another way which the cocoa butter molecules find more favourable to exist in.  This means that if you give the molecules time (like in old chocolate) or energy (by melting it), the molecules can rearrange themselves and form a crystal which melts at a higher temperature and so it no longer melts in your mouth causing the gritty sensation.

Good Chocolate

Bad Chocolate

Sweet molecules

The most simple forms of sugars are glucose, fructose and galactose.  The most common sugar used in table or granulated sugar is sucrose; this is a molecule comprised of one unit of glucose and one unit of fructose chemically bonded to one another.  More recently, artificial sweeteners have been developed which are lower in calories such as thaumatin.

Glucose

Sucrose

Thaumatin

Glucose is a chiral molecule which means that its three dimensional shape is important; there are two optical isomers D-glucose and L-glucose but the latter is rarely found in nature.  The crystal structure of D-glucose was first determined in 1962 by Killean, Ferrier and Young  as a solid which also contains water (called a hydrate).  The structure of fructose was first determined in 1977 by Kanters, Roelofsen, Alblas and Meinders.  The crystal structure of galactose was first determined by Longchambon, Ohannesian, Avenel and Neuman in 1975.  The crystal structure of sucrose was determined by Brown and Levy in 1963.