I am writing a review on crystallisation, i.e., on how crystals like salt, ice, etc, form. So I am reading lots of scientific papers on crystallisation. A lot of them are very technical but I came across one on chocolate. From this I learnt that there are six forms of chocolate, of which the tastiest is number five and the white bloom that sometimes forms on chocolate is number six.

By this I mean that cocoa butter, which is part of chocolate, is crystalline and has six different crystalline forms (called polymorphs in the trade). This is like many other substances, for example diamond and graphite (the ‘lead’ in pencils) are two different crystalline forms of carbon. Both diamond and graphite are pure carbon and both are crystals but the carbon atoms are arranged differently in diamond and in graphite.

So cocoa butter has six different crystals. Type five has the best texture, so it’s the one chocolate makers try to make chocolate in. However, type five can transform to type six if the chocolate is not stored correctly. The cocoa molecules are differently arranged in type five and in type six. So, when a small part of the chocolate transforms to type six it changes shape – it’s then a square peg in a round hole. The claim is that it then buckles to relieve the strain it is under as a result of not fitting in with the rest of the cocoa butter. Then it is many many buckling mini (perhaps a thousandth of a millimetre) crystals that is the white bloom.

Despite eating a fair amount of chocolate, I knew nothing of this until I started on the review. Amazing, the fascinating science literally under your nose.