The physics and chemistry of cocoa beans and cocoa products is very complex and changes throughout the life of the bean, depending on the processing it receives.
The following gives an indication of the changes in the bean through its life, together with some references that give further more detailed information on the physics and chemistry of cocoa beans.
Cocoa beans are the seeds of the tree Theobroma cacao. Each seed consists of two cotyledons (the nib) and a small embryo plant, all enclosed in a skin (the shell). The cotyledons store the food for the developing plant and become the first two leaves of the plant when the seed germinates. The food store consists of fat, known as cocoa butter, which amounts to about half the weight of the dry seed. The quantity of fat and its properties such as melting point and hardness depend on the variety of cocoa and the environmental conditions.
The seeds are fermented which causes many chemical changes in both the pulp surrounding the seeds and within the seeds themselves. These changes cause the chocolate flavour to develop and the seeds to change colour. The seeds are then dried and despatched to processors as the raw material for the production of cocoa mass, cocoa powder and cocoa butter. The first stage of processing includes roasting the beans, to change the colour and flavour, and shell removal. After roasting and deshelling an alkalising process can take place, to alter flavour and colour.
One analysis of the chemical composition of beans after fermentation and drying is as follows:
|Nib % Maximum||Shell % Maximum|
|Fat (cocoa butter, shell fat)||57||5.9|
This gives an indication of the chemical composition of the bean but it must be remembered that this will vary depending on the type of bean, the quality of the fermentation and drying and the subsequent processing of the bean.
Cocoa mass is produced by grinding the nib of the cocoa bean. The quality of the cocoa liquor will depend on the beans used. Manufacturers often blend different types of beans to gain the required quality, flavour and taste. The cocoa liquor can undergo further roasting and alkalisation to alter the colour and flavour which will also alter its chemical composition.
The fat or cocoa butter can be extracted from the bean in a number of ways. Pure press butter is extracted from the cocoa mass by horizontal presses. Sub-standard cocoa beans can be pressed without deshelling by using continuous expeller presses. Pure press butter needs no cleaning but it is often deodourised. A solvent extraction process can be used to extract butter from the cake residue left after the expeller process, this type of butter must be refined.
Cocoa butter obtained by pressing the cocoa nib exhibits the following properties: brittle fracture below 20ºC, a melting point about 35ºC with softening around 30-32ºC.
Cocoa butter is composed of a number of glycerides. Two studies established that the percentage of the constituent glycerides is as follows:
|Trisaturated||2.5 to 3.0|
|Stearo-diolein||6 to 12|
|Palmito-diolein||7 to 8|
|Oleo-distearin||18 to 22|
|Oleo-palmitostearin||52 to 57|
Cocoa powder is formed from the cocoa mass. Presses are used to remove some of the fat and leave a solid material called cocoa press cake. These cakes are then crushed to form cocoa powder. The processing can be altered to produce cocoa powders of different composition and with different levels of fat.
An indication of the composition of cocoa powder is as follows, but it must be remembered that this will be different depending on the roasting, alkalisation and pressing processes undertaken:
|pH (10% suspension)||5.7|
|Water soluble ash %||2.2|
|Alkalinity of water soluble ash as K2O in original cocoa %||0.8|
|Phosphate (as P2O5) %||1.9|
|Chloride (as NaCl) %||0.04|
|Ash insoluble in 50% HCl||0.08|
|Shell % (calculated to unalkalised nib)||1.4|
|Nitrogen (corrected for alkaloids) %||3.4|
|Nitrogen corrected for alkaloids x 6.25 %||21.2|
Beckett S.T., Industrial chocolate manufacture and use. Second edition. Blackie Academic & Professional, 1994
Minifie B.W., Chocolate, cocoa, and confectionery science and technology. Third edition. Van Nostrand Reinhold, 1989
Dand R., The international cocoa trade. Woodhead Publishing, 1993
Cook L.R. and Meursing E.H., Chocolate production and use. Revised edition. Harcourt Brace Johanovich, 1982
The cocoa manual. A guide to De Zaan's cocoa products. Cacao de Zaan, 1993