The application of an electric field helps chocolate flow more easily, removing the need for the world’s favorite treat to be so rich in fat. The effect is not large enough to turn candy bars into health food, even if you ignore the sugar, but could still lead to serious calorie reductions. Has Willy Wonka finally grown up?
Fat has its own taste and improves our appreciation of other flavors. However, the concentrations seen in a typical chocolate bar are set not by taste considerations but the challenges of production. Efforts to make reduced-fat chocolate have foundered on the fact that these products are more viscous, or resistant to flowing, and therefore don’t move easily through mass production pipelines.
Past failures to produce low-fat chocolate are “deeply related to the basic science of soft matter,” Professor Rongjia Tao of Temple University, Pennsylvania reports in Proceedings of the National Academy of Sciences. “Most people think of chocolate as a solid because this is how they buy and eat it. To the chocolate maker, however, chocolate is a liquid for the whole process of production and only solidified just before it is ready to be packed and sent to the warehouse or store.”
But help is on its way. Tao applied a 1,600 Volts/centimeter (4,000 Volts/inch) electric field along the direction of flow of chocolate samples from major manufacturers heated to 40º C (104º F), which reduced the liquid chocolate’s viscosity and increased its density, reducing the need for as much fat.
The crucial metric, Tao reports, is something rheologists (scientists who study flow) have dubbed maximally random jammed (MRJ) density. “When the concentration of cocoa solid is high, close to the MRJ density, removing a small amount of fat will jam the chocolate flow,” the paper observes.
Chocolate made entirely of cocoa solids and cocoa butter, without milk or sugar, must have at least 36 percent fat if it is to avoid jamming.
However, an electric field causes cocoa particles to clump together, breaking the rotational symmetry of the liquid and making the chocolate flow more easily, even with lower levels of fat.
Having established that the electric field reduced viscosity, Tao measured how much fat he could take out before jamming occurred. “We can effectively reduce the viscosity of all kinds of chocolate by 40-50 percent,” Tao and his co-authors reported. “Therefore, we can easily reduce the fat level by 10 percent or more for all these samples.”
Electric fields have been used to change the flow of fluids before, but traditionally this has been done to increase viscosity, by creating an electric field perpendicular to the direction of flow, rather than along it.
