Rooks Heath at “Chocolate Unwrapped”

Physics and Chocolate

Believe it or not physics is involved in chocolate production. Without the careful use of temperature and pressure we wouldn’t have the wonderful confectionary that adults and children alike have grown to love.

On October 13th year 12 physics students went to the “chocolate unwrapped” exhibition to learn more about the production of chocolate.

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L to R: Manikandan, Matthew, Pameer, Aslam, Wing Chung, Sulaxan and Alfie just before going into the exhibition.

Chocolate is produced from the ripe seed of the tropical Theobroma Cacao tree and was initially cultivated in Mexico, Central and South America.


The seeds naturally have an intense bitter taste so must be fermented to develop the flavour. After fermentation, the beans are dried and then roasted (requiring a high temperature). The shell is then removed to produce cacoa nibs which are then ground (high pressure) to produce cocoa mass (pure chocolate in rough form).

Cocoa mass is usually liquefied (high temperatures and/or pressure are used to form what is commonly called chocolate liquor) and then moulded with or without other ingredients to form many types of chocolate products such as milk chocolate.

Chocolate liquor may be processed into two components cocoa solids and cocoa butter, the latter being used for white chocolate.


The penultimate process of chocolate production is called conching. A conche is a container filled with metal beads, which acts as grinders to reduce the gritty and uneven texture of the chocolate. The refined and blended chocolate mass is kept in a liquid state by friction and heat. The length of the conching process determines the final smoothness and quality of the chocolate. High-quality chocolate is conched for about 72 hours. After the process is complete, the chocolate mass is stored in tanks heated to approximately 45-50 degrees Celsius until final processing.


The final process is called tempering which involves manipulating the temperature to produce the most stable crystals to provide the best appearance, texture and prevention of degradation.

Crystal Melting temp. Notes
I 17 °C Soft, crumbly, melts too easily
II 21 °C Soft, crumbly, melts too easily
III 26 °C Firm, poor snap, melts too easily
IV 28 °C Firm, good snap, melts too easily
V 34 °C Glossy, firm, best snap, melts near body temperature (37 °C)
VI 36 °C Hard, takes weeks to form

Generally the chocolate is first heated to 45 degrees Celsius to melt all the crystals. It is then allowed to cool to about 27 degrees to allow crystal types IV and V to form. At this temperature, the chocolate has to be agitated to create many small crystal “seeds” which serve as nuclei to create small crystals in the chocolate. The chocolate is then heated to about 31 degrees Celsius to get rid of type IV crystals. This process can be done manually but most chocolate manufacturers use a tempering machine with computer controls to produce consistently tempered chocolate. The Greer temper meter can measure the degree of temper at any required time.


LCM coating machines come with continuous tempering and are equipped with level controls.


The students are listening to one of the exhibitors talking about his chocolates.


The chocolate mixer


—and here is some we made earlier.


Of course once the chocolate has been produced this may not be the end of its processing. Chocolate is often use to decorate and cover other confectionary like cakes and for this it has to be able to flow. The flow characteristics (viscosity) are important; too runny (low viscosity) and the chocolate won’t “stick” to the cake and certain moulding and depositing machines will not work right; too thick (high viscosity) and the chocolate is difficult to pump from one part of the factory to another and the apparatus may get blocked, or more importantly the manufacturers will lose money by using too much chocolate. The viscosity of the chocolate has to be carefully controlled.

Chocolate viscosity is a physical property that is carefully monitored and tightly controlled within defined limits. It is measured in various ways with the most basic apparatus being the falling ball viscometer.


The Höppler principle is used to measure the viscosity of Newtonian liquid by measuring the time required for a ball to fall under gravity through a sample-filled tube that is inclined at an angle. The average time of three tests is taken; the result is converted into a viscosity value using a simple formula.

There are several factors that affect viscosity of chocolate. Increasing moisture and/or the particle size of the mixture will create higher viscosity. Conversely, increasing temperature and adding emulsifiers will tend to reduce viscosity.


The chocolate chef.


Tasting some of the finished products.


A chocolate sculpture

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