Chocolate Week – Part 1

For Part 1 of Chocolate Week we look at chocolate itself and some of the science behind how it’s made.

 

The cocoa, or cacao bean

The cacao bean, the key ingredient of chocolate, originates from South America and was originally brought to Europe by the Spanish in the 16th Century. The bean itself is found within a pod growing on the Theobroma cacao tree, with each pod containing between 20 and 60 beans. While originally found in South America, the major cultivators of cacao are now Cote d’Ivoire, Ghana and Indonesia.

Cacao pod

Chocolate as we know it is a relatively recent innovation. The original chocolate, as produced by the Aztecs and brought to Europe by the Spanish, involved the cooking of cacao beans with hot peppers, vanilla and corn flour. The amount of hot peppers was reduced upon introduction to Europe to better suit tastes there, and it eventually evolved into a sweetened drink, which spread throughout Europe in the 17th century. To produce this new form of chocolate, rather than using the cacao beans whole as the Aztecs did, the beans were ground and formed into bars of what is now known as cocoa mass.

Beans in the cacao pod

When cacao pods are first picked, they are left to ferment for several days to help extraction of the beans. The beans are then left to ferment for several more days, with the process causing the formation of new chemicals in the beans, and then dried. Tasting a cacao bean at this stage, the taste does not resemble chocolate as we know it. In fact it is an almost sour taste, while the fermentation process gives the bean a rather “off” tangy smell. The flavours we recognise as chocolate are a result of a roasting process carried out prior to the grinding of the beans. Indeed, tasting the nibs of the roasted beans gives some idea of the chocolate tastes.

Roasted cacao beans

The cacao beans contain high amounts of fat, starch and protein, and in early forms of chocolate this fat content was generally disliked. To overcome this problem, presses were developed to remove the fat, which forms cocoa butter. However, during the grinding process used today, the fats coat the ground cocoa powder and produced chocolate liquor, a mass which when tasted does reseamble something closer to chocolate, however I found to be quite bitter. Modern chocolate normally contains at least 30% chocolate butter.

 

From cacao to chocolate

The chocolate liquor is combined with more cocoa butter, sugar and milk solids and ground to an extremely fine powder. The finer the grinding, the smoother the resulting chocolate will be, however will produce a thicker chocolate.

The mixture is then heated during a process called “conching”, where the temperature is increased above 55°C, stirred constantly, and exposed to circulating air. This process removes many of the volatile chemicals in the mixture, reducing the tart flavours and developing the flavours we normally associate with chocolate. The constant stirring also makes a smooth emulsion (particles suspended in liquid), with a smoother emulsion resulting in a smoother chocolate.

Conching chocolate. The rollers are producing a smooth emulsion while the open vat allows chemicals to evaporate away.

Following the conching, the mixture is cooled to crystallise the cocoa butter and form solid chocolate. While this may sound a straight forward process, it does require care. When substances crystallise, they can form several different types of crystals, and cocoa butter can form six, and the formation of these crystals will change the chocolate’s properties. Some crystals will result in chocolate being extremely hard, while other types will affect the melting temperature, making it either too high or too low. Small crystals are also preferred as large crystals will give the chocolate a gritty feel, with smaller crystals also giving chocolate the shine that makes it so appetising.

Controlling the formation of these crystals is called tempering, and involves careful control of the chocolate temperature and principles learnt from chemistry. The crystals which produce the perfect chocolate form between 18-25°C, however the process is much more complicated than just a single temperature.

 

Tempering chemistry

To begin tempering chocolate, it must be heated to a temperature which melts any existing cocoa butter crystals, above 44°C. However raising the temperature too high will ruin the emulsion formed during the conching process, making the chocolate coarse and gritty.

A small-scale tempering machine.

Once the cocoa butter crystals have melted, the liquid is cooled to below 28°C to begin the crystal reformation. At this temperature there are two types of crystals forming, but while the crystals are forming the mixture is constantly stirred which breaks up these crystals into small pieces. As more crystals form and are broken the liquid thickens, and just before it can set the temperature is raised to 31°C. At this temperature, one type of crystal which has a low melting point will melt, however the other type of crystal, which has a melting temperature of about 33°C, will remain. These higher melting temperature crystals are the most desirable form to have, producing all the best qualities of chocolate.

Because the tempering process has resulted in only the best type of crystal for chocolate, when the chocolate liquid is then set, the crystals will grow still in the most desirable form. And because the constant stirring has made lots of small crystals, the crystals will not become overlay large. This means that after going through the tempering process, the chocolate will have only the crystal type that gives the best melting temperature, the perfect smoothness and the deepest shine.

After this process however, some cocoa butter crystals may not be completely stable. When heated to above 20°C, small amounts of the cocoa butter may slowly melt and seep out of the chocolate. When the cocoa butter reaches the surface of the chocolate it recrystallises and forms those white areas sometimes found on chocolate.

 

Thanks again to Brendan Somerville, chief taster at Haigh’s.

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