Chocolate is made from the seeds of the tree Theobroma cacao. Theobroma is Greek for 'food of the gods'. The ancient Aztecs venerated the cacao tree and used its beans as a form of currency. They saw the tree as a source of strength and wealth and assigned their god Quetzalcoatl its guardian.

The Aztecs discovered that by crushing the beans into a paste and adding spices, they could make a refreshing and nourishing drink. This drink would have been very bitter, unlike our chocolate drinks today. 16th century European explorers brought the drink back from their travels, added sweeter flavorings, and soon it was popular as an expensive luxury.

The first chocolate bars

In the 1800s, solid chocolate became popular, with the invention of moulding processes. Mechanical grinders crushed cocoa beans to a fine powder that could be heated and poured into moulds, forming shapes as it cooled.

Dutchman Coenrad Van Houten perfected the extraction of cocoa butter from cocoa beans in 1825. The beans are crushed to a paste, which is subjected to very high pressure, forming chocolate liquor and cocoa butter. The extracted butter is smoothed and treated to remove any odours.

In the 1880s, Rudolphe Lindt of Switzerland started adding extra cocoa butter during chocolate manufacture, to make it smoother and glossier. Cocoa butter melts at around 97°F, which is human body temperature. That's why chocolate melts in the mouth. ------Milk chocolate------

In 1875, Swiss Daniel Peter perfected the manufacture of milk chocolate, which is sweeter and smoother than dark chocolate. Nestlé's recently-invented condensed milk was easy to mix with cocoa paste, unlike liquid milk.

Cadbury's 'Dairy Milk', first developed in 1905, is the UK's most popular chocolate bar. Milk chocolate is now the world's best-selling variety. Chocolate craving The love of chocolate goes beyond the call of sweetness. Chocolate can induce craving in a way that other sugary products like toffee or marshmallow don't. Chocolate makes us feel good, but can it really be addictive? --------Why chocolate makes us feel good--------

Several more obscure chocolate ingredients seem to act by affecting the brain's own neurotransmitter network.

Neurotransmitters are the chemical messengers of the brain. They work by transporting electrical signals between nerve cells. These signals cause changes in the sensations and emotions that we experience.