Colored Chocolate: Edible Diffraction Grating?

|Difficulty level: Easy|

Would you like to eat a diffraction grating? Yes! Read right “an edible diffraction grating”, which is not only the concept of optical physics but also ready to hit the food industry soon in the form of colored chocolate or say rainbow chocolate.

What provides chocolate its color?

Mostly, the chocolate we consume is colored in various shades of brown and white. Chocolates are made from Cacao seed. The fermented cacao seeds are grounded after drying and roasting to get rough unadulterated chocolate. This unadulterated chocolate is heated to get liquefied chocolate, called chocolate liquor. This liquor is processed into two components-cocoa solid and cocoa butter. These two components are what we consume as chocolate. Cocoa solid is dark brown in color whereas cocoa butter is white. These two presents in different proportions are responsible for the color of chocolate. Another material such as powdered milk and sugar is added to provide flavor. Dark chocolate does not contain sugar and milk; hence it is bitter in taste. White chocolate contains only cocoa butter which provides its color.

Can we have colored chocolate?

The natural color of chocolate is brown or white. We can get colorful chocolate in the market. Traditionally, colored chocolates are made by coating the white chocolate or using additive food colors in white chocolate. But these artificial colors might pose health risks in sensitive people.

Is there a way to make multi-colored chocolate without using artificial ingredients?

Samy Kamkar, founder of Internet Security Company, Openpath has created colored chocolate[1]. He used a 3-D mold textured with spikes (sawtooth wave pattern) of few micrometers. When melted chocolate is poured inside a mold, its structure gets fabricated with the inverse pattern of the mold. Continued to cool down to get a solid form. Texture fabricated acts as a diffraction grating and results in a rainbow color effect when light falls on it.

A similar aim but with a different story came from Swiss University ETH, Zurich[2], where researchers of different fields went for a coffee break and strike with the idea of preparing colored chocolate without the use of color agents. They started working on the idea and had recently filed a patent for making colored chocolate that glows in light with rainbow effect by imprinting the special structure on the surface of the chocolate. They designed their molds with e-beam lithography which is used to etch the nanopattern which can be in the form of elongations, scales, or lines.

What is the principle behind the colors of colored chocolate made using textured mold?

The basic idea behind both the stories lies in the morphology of the chocolate surface. Compared to the plane surface, these Nanoscale patterns are bulged out a few nanometers height and are spaced in the same nanometer range as of height, thus these Nanoscale fabrications are analogous to the diffraction grating. When the light of different wavelength falls on the different parts of these elongations of the surface chocolate, the incident light gets singly or multi reflected.

Due to the interference property of light, these reflected rays get constructively or destructively interfere. The constructive interference at different parts of surface results to different colors of light (which depends on the wavelength of light incident on it) and different intensities depending on the angle of light incident on it, which is called iridescence, similar to soap thin films and CDs when rotated or seen at a different angle, shows the different color. The scale of nanopatterns on the surface of chocolate is comparable to the wavelength of light, thus different parts of the surface of chocolate show a particular color of light only whose wavelength is comparable to that spacing of nanopattern.

The chocolate with vibrant colors and with no added colors, no harmful coatings will soon be in our reach. No one had thought that the chocolate industry will also get upgraded like this with nanotechnology. Thus, said truly: the limit to the ideas is the sky! No matter how much the things are developed, there is always room for improvement.

Can this rainbow effect survive after the melting of chocolate, what you say?

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