Chocolate Forensics

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Break a cold piece of chocolate right out of the refrigerator then break one at room temperature. If you take a moment to look at the broken surfaces you'll notice that they look very different. The warm fractured surface is noticeably rougher. Placing both on your tongue, you'll notice that the warmer one seems to have a more intense flavor. The amount of flavor we sense depends in part on the area available on the surface we are tasting. All you need to do is crunch a life saver to observe this. These observations lead to an interesting question: Is there an optimal temperature for breaking chocolate to maximize the flavor?

Our initial investigation focused on how the surface area of fractured chocolate is related to temperature. Chocolate was heated or cooled to several temperatures in a computer controlled incubator, and broken at a controlled rate in a custom made, automated 3-point bending apparatus. The samples were photographed and the surfaces were measured using a Scanning Laser Microscope (SLM). Finally, the data was analyzed using Scale Sensitive Fractal Analysis.

Broken chocolate at 35C. View chocolate at other temperatures...

The photographs show fractured chocolate surfaces at the same scale using the same lighting and lens settings. A low incident angle for the light was used to emphasize the texture. The texture clearly changes as temperature changes. Roughness appears to increase as temperature increases. Also, the samples fractured at higher temperatures appeared to have roughness at a larger scale than colder fractures.

As it turns out, the amount of surface area is dependent on the scale of observation. At the limit of the SLM's resolution, chocolate broken at 25°C shows the most surface area, with a relative area of 2.25. Using the SLM, a 5mm x 3mm measurement was made with a resolution of 10µm in each direction for fractured surfaces at each temperature. Each topographical data set was leveled to a best-fit plane, and an area scale analysis was performed. At each area, a coefficient of correlation for relative area and temperature was computed. The result is a curve with a remarkably high peak.

The bell curve peak indicates that at a specific scale there is a highly correlated relationship between fracture temperature and relative area. This opens up the field of chocolate forensics-given the surface measurement, the temperature of fracture can be determined with 99% certainty.

While we may know a lot about broken chocolate we have yet to determine the scale at which flavor perception occurs. In order to do this we will need lots more chocolate and many volunteers.

Download a video clip (AVI) of the chocolate breaking process...

More photographs and charts...

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Last modified: October 04, 2007 09:53:08