Tag: chocolate

Surface Fat Gives Chocolate’s Mouthfeel
Understanding the interactions of food and our mouths is incredibly difficult. There are lots of changes going on: shape changes from chewing, viscosity changes as saliva lubricates the food, and, sometimes, phase changes from the heat of our bodies. Add to that the sensitivity of our papillae-covered tongues, and it’s a lot to manage all at once. Recently, researchers have turned to 3D-printing to create a more realistic lab version of our mouths.
The team 3D-printed a papillae pattern matching the size and distribution of an actual human tongue, then molded that pattern onto a silicone elastomer. The result? A replica tongue that matches a human one in terms of softness, wettability, and surface roughness. They then attached their tongue to a rheometer to measure the friction between the tongue and dark chocolate.
Their experiments simulated licking, eating, and swallowing the confection. During licking and eating, they found that the chocolate was lubricated by a layer of fat directly between the tongue and the food. Their results suggest that one way to make healthier chocolate options is to concentrate fat into the surface layer of the chocolate while lowering the fat content inside the bar. (Image credit: D. Ramoskaite; research credit: S. Soltanahmadi et al.; via APS Physics)
February 14, 2023
Giving Chocolate that Smooth Finish
Anyone who’s tried to make chocolate confections at home can tell you that achieving that perfect smooth consistency isn’t easy. It was only after Rodolphe Lindt invented the process of conching in 1879 that anyone enjoyed smooth chocolate. Conching is what allows granular solids like sugar, milk and cocoa powders to mix with liquid cocoa butter into a smooth, homogeneous liquid. Although the process has been known for more than a century, it’s only recently that researchers have unraveled the underlying physics that enables it.
One of the key parameters to conching is the a mixture’s jamming volume fraction; in other words, the point where the fraction of solid particles in the mixture is too high for it to flow freely. In the first stage of conching, the solid particulates and a small amount of liquid are stirred and slowly heated. The mechanical action of stirring breaks up aggregates and raises the jamming volume fraction. By the end of the dry conche, the mixture could flow, in theory, except that it fractures at a lower stress than what’s necessary to flow.
At this point, chocolatiers add the remainder of the liquid ingredients. That infusion of moisture decreases the friction between solid particles and further raises the jamming volume fraction. With the system now far below that jamming point, the mixture transforms into a freely-flowing, smooth fluid. By understanding the intricacies of the process, scientists hope to reduce the energy necessary in chocolate production and similar industrial processes. (Image credit: A. Stein; research credit: E. Blanco et al.; via Physics World; submitted by Kam-Yung Soh)
May 29, 2019
Bonbon Coatings
If you’ve ever bitten into a chocolate-covered bonbon, you may have noticed that the candy’s chocolate coating is remarkably uniform. Inspired by this observation, a group of engineers have investigated how viscous fluids poured over a curved surface flow and solidify; their findings were published this week.
Rather than heated chocolate, the group used polymer-filled fluids that cure and harden over time. Interestingly, they found that the final shell is quite uniform and that its thickness does not depend on the pouring technique. Instead, they can predict the final shell thickness based on the radius of the mold and the rheological properties of the fluid–specifically its density, viscosity, and curing time. The reason for this is that the time it takes for the fluid to drain and coat the mold is much shorter than the time it takes for the polymer to cure. As a result, the amount of fluid that sticks to the mold depends on geometry and fluid properties – not how the fluid was poured.
Amateur confectioners rejoice: pouring uniform chocolate coatings may be easier than you thought! (Image credit: MIT News, video; research credit: A. Lee et al.)
April 8, 2016
Chocolate Fountain
Amidst your holiday celebrations, you may have encountered a chocolate fountain. In a recent paper, applied mathematicians have laid out the physics behind these delicious decorations, and it turns out they are an excellent introduction to many fluids concepts. Molten chocolate is a mildly shear-thinning, non-Newtonian fluid, meaning that it becomes less viscous when deformed. This adds a wrinkle to the mathematics describing the flow, but only a little one. The researchers divide the flow into three regimes: pipe flow driving the chocolate up the inside of the fountain, thin-film flow over the fountain’s domes, and, finally, the curtain of falling chocolate where foodstuffs are dipped. The final regime is the most mathematically challenging and may be the most fascinating. The authors found that the free-falling curtain of liquid pulls inward as it falls due to surface tension. Their paper is quite approachable, and I recommend those of you with mathematical inclinations check it out. (Image credit: P. Gorbould; research credit: A. Townsend and H. Wilson)
December 30, 2015