The Chemistry of Chocolate
Cocoa originates from beans of the cocoa tree and it is an important commodity in the
world and the main ingredient in chocolate manufacture. Its value and quality are related to
unique and complex flavors. Cacao tree or a theobroma cacao belongs to the Malvaceae family,
it is tropical plant indigenous to the equatorial regions of the Americas. The fruits of the cacao
tree are squash‐like pods that grow proximal to the trunk and to thicker branches and each cocoa
pod contain about 35 to 50 beans embedded in a mucilaginous pulp.
Chocolate is composed of cocoa solids, cocoa butter and sugar and at room temperature,
it is in solid form. The melting point of a substance is the temperature at which it experiences a
change, so it will turn from solid to liquid or a change from one common state of matter to
another. One of the key reasons cocoa or chocolate melts in our mouth is because of the
relationship of our body temperature and its melting point. Our body temperature is 98.6 degrees
and the melting point of chocolate is around ten degrees lower. If you held a chocolate bar in
your hand for too long, the chocolate will probably melt on your hand. If that is the case then
chocolate will melt even faster in our mouth, unless we drank something cold, or out in the cold
with our mouth open, usually between 75 and 80 degrees Fahrenheit, pretty close to the melting
point of chocolate. As the cocoa reaches its melting point in the high 80 degrees Fahrenheit it
will turn into a viscous liquid. In chemistry, the viscosity of a liquid is measured through the
fluid’s thickness, and how slowly it flows. The particle size of the cocoa powder used in
chocolate milk is 10–30 μm and ideally less than 0.5% of particles present that has a particle size
above 75 μm. The distinctive smooth texture of cocoa or chocolates is achieved through the
process of conching.
Conching is a mixing process that evenly distributes cocoa butter within chocolate and
may act as a polisher of the particles. It promotes flavor development through frictional heat,
release of volatiles and acids, and oxidation. It produces smooth molten chocolate by breaking
down lumps of ingredients into finer grains and reducing friction between particles. Without this
process chocolate will have a gritty texture. This is because the ingredients form rough, irregular
clumps that do not flow smoothly when mixed with cocoa butter using other methods.
Cocoa powder quality is determined by its color, flavor, dispersion, and flow properties,
which can be controlled via tempering. Design of a cocoa powder tempering profile, however,
requires that the mechanism of cocoa butter crystallization in cocoa powder be fully
understood. Differential scanning calorimetry (DSC) and high performance liquid
chromatography (HPLC) were used to determine the thermal properties and glyceride
composition. In addition visual characterization of the crystallites was obtained with polarized
light microscopy.
Crystals were formed under controlled static or motionless conditions at formation
temperatures of 26, 28, 30, 32 and 33°C. Preparatory techniques were developed using laminated
polyethylene with plastic hoops in order to grow the crystals for isolation and visual
identification by PLM prior to DSC assay. Moreover cocoa butter was crystallized statically
from the melt to various temperatures in the range of -20 to 26° and annealed for up to 45 days.
During this period, the polymorphism of the solid state was monitored through differential
scanning calorimetry and power x-ray diffraction. In manufacturing cocoas manufacturers
generally use more than one type of bean in their products and those different beans have to be
blended together to the required formula. The cocoa liquor is pressed to extract the cocoa butter,
leaving a solid mass called cocoa presscake. The amount of butter extracted from the liquor is
controlled by the manufacturer to produce presscake with different proportions of fat. The
processing now takes two different directions, first is using cocoa butter for the manufacture of
chocolate and second cocoa presscake is broken into small pieces to form kibbled presscake,
which is then pulverised to form cocoa powder.
Cocoa liquor is used to produce chocolate through the addition of cocoa butter. The
proportions of the different ingredients depend on the type of chocolate being made. The mixture
then undergoes a refining process by travelling through a series of rollers until a smooth paste is
formed. The next process, conching, further develops flavor and texture. An alternative to
conching is an emulsifying process using a machine that works like an egg beater. After that
mixture is then tempered or passed through a heating, cooling and reheating process. This
prevents discoloration and fat bloom in the product by preventing certain crystalline formations
of cocoa butter developing. Then mixture is put into moulds or used for enrobing fillings and
cooled in a cooling chamber. Lastly the chocolate is packaged for distribution to retail outlets.
References:
Processing
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Cocoa.
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Relationship between Crystallization Behavior and Structure in Cocoa Butter. (n.d.). Retrieved
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https://pubs.acs.org/doi/abs/10.1021/cg025580l.
Aprotosoaie, A. C., Luca, S. V., & Miron, A. (2015, November 18). Flavor Chemistry of Cocoa
and Cocoa Products-An Overview. Retrieved from
https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12180.
Singh, R. P., & Cook, L. R. (2018, November 1). Cocoa. Retrieved from
https://www.britannica.com/topic/cocoa-food.
Kotb, H. (Reporter). (2011, February 12). The Chemistry of Chocolate. [Television series
episode]. NBC Learn.
Retrieved
from https://archives.nbclearn.com/portal/site/k12/browse/?cuecard=52212
Written by: Reine A.