About Chocolate | Tempering
Many of the web-site readers have expressed an interest in knowing a little bit about the nature of the chocolate manufacturing. I have compiled a brief description of the process that should give you some more information than you presently have The information used is primarily provided through the Cocoa Barry Institute – a leader in chocolate development and research – particularly the French masters P. Bertrand and P. Marand. The institute is a part of Cocoa Barry, one of the major French manufacturers and an innovator in chocolate manufacturing and processing. As a result of a global company merger, the company is now named Barry-Callebaut.
Chocolate making is a delicate business involving many different stages. The stage that we are interested in now is how the chocolate is handled, prepared and stored. The result of the mechanical process, described in the process section notes, is the cocoa mass that naturally contains about 54% cocoa butter. Technically, couveture is a chocolate mixture containing, by international standards, at least 31 % cocoa butter.
Cocoa butter is a mixture of several triglycerides – primarily oleic, stearic, and palmitic acids. These fatty acids have different melting points. Another interesting fact about cocoa butter’s properties is it is polymorphous, meaning that it crystallises into different forms of crystals, of which five are predominant. These crystals, like the fatty acids, have different melting points. Of the five major crystals, the only crystal that is stable is the beta crystal. Throughout the different crystallisation phases, the cocoa butter undergoes changes in size. It is during the cocoa butter’s most stable phase that it has the least volume. It applies to couveture as well. Finally, chocolate is monotrop – it has a tendency to crystallise in its most stable state. This process is very slow, so the objective of the tempering process is to speed the process up.
Tempering can be defined as a thermal and mechanical procedure of crystal orientation, by selecting the most stable crystals. Stable beta crystals are created in the melted chocolate, which will help in the proper crystallisation of the entire cocoa butter later during cooling. For successful tempering, these stable crystal seeds have to be created. This is called the pre-crystallisation phase. Pre-crystallisation depends not only on the temperature at which the product is set, but also the duration of this temperature change and the amount it is agitated. Agitation creates thermal change within the chocolate that can result in poor tempering. The quantity of crystal seeds is very important as too few stable beta crystals results in a non-moulded chocolate surface that will have a grainy texture after solidification. This is called under-tempering. If there are too many crystal seeds, the turning out after moulding (poor contraction) will be more difficult, and a white film may also may occur. This is called over-tempering.
There are many types of tempering techniques – the most classic is manual tempering. In this type of tempering the chocolate is heated to 40-45 C (104-113 F). It is then worked on a granite or marble table with a spatula and a metal scraper to reduce the temperature: for dark chocolate down to 28 C (82.5 F); milk, white or coloured chocolate 26 C (79 F). The chocolate begins to thicken as the beta crystals multiply. The mixture is then heated to 31-33 C (88-91.5F) for dark chocolate and to 29-30 C (84-87F) for the others. The beta crystals now predominate.
The chocolate is then moulded or worked to its desired form and cooled either by radiation (a Cooling tunnel) or by convection (a cold room or refrigerator). The proper cooling prevents unstable crystals from forming.
If the thermal or hygrometric changes during tempering or storing are too high, they can lead to fat bloom (when the cocoa butter rises to the surface of the chocolate) or sugar bloom (where the sugar, not fat rises to the surface). These two white or milky features on chocolate product negatively affect the appearance, texture and taste of the chocolate. What happens is that the fat or sugar elements migrate from the chocolate centre to the surface, creating mono-unsaturated crystals. The detailed reasons are many, but suffice it to say that only if the tempering, cooling and storage of the chocolate is properly mastered can these negative results be avoided.
The result of good tempering is a fine glossy surface with a high shine, good snap, and a pleasing texture.
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