Researchers Reveal the Formula for the Perfect Bonbon Shell

Dessert aficionados know that the secret to a perfect bonbon is a smooth, wafer-thin chocolate coating. While expert chocolatiers perfected the method of creating that coating centuries ago, the science behind the technique hasn't been clear until now. In a study recently published in the journal Nature Communications [PDF], researchers from MIT shared their formula for turning a liquid coating into an even, solid shell of any specific thickness.

The inspiration for the study came from watching videos of chocolatiers making bonbons and other chocolate-coated treats. The chocolate-makers seemed to create shells of consistent thickness every time by pouring chocolate into molds and flipping them upside-down to let the excess liquid drain out. When the researchers tried replicating this technique using a liquid polymer solution in place of chocolate, they found that their shells also turned out evenly thick all around.

Their next step was to figure out what exactly was determining the shell's thickness. To do this they played around with several variables, including the size of the mold and the viscosity of the liquid. Solutions that were drizzled over wider molds resulted in thicker shells, as it took more time for them to coat the entire shape. Polymers that took longer to set flowed faster, maker for a thinner final product.

Using this observation, the team was able to figure out a simple trick for creating a perfect film of their preferred thickness. By giving the liquid some time to thicken up before drizzling it on, they produced shells that were slightly thicker. By pouring it on right away, more of the liquid drained off and the shells they were left with were thinner.

While the pursuit of the perfect bonbon is admirable in itself, the team's exact formula (the square root of the chocolate's viscosity, times the mold's radius, divided by the curing time of the liquid, times its density, and the acceleration of gravity as the chocolate flows down the mold) could have plenty of applications outside of the culinary realm. For one, it could be used by pharmaceutical companies to create more precise gelatin coatings for pills that dissolve more quickly or slowly in the body. The findings could also be potentially used to make artificial vesicles, packaging films, or bodies for airplanes and rocket ships.

Learn more about the experiment in the video above.

Header/banner images courtesy of MIT via YouTube.