butter, and can replace some of the fattening oils in foods such as mayonnaise and salad dressings. However, these innovations have not been without their own problems. Less fatty chocolates have a harder texture. In an attempt to counter this, biochemist Bettina Wolf and students at the University of Nottingham tried adding limonene to low-fat chocolate. Limonene is a citrus fruit-derived oil-soluble substance that compensates for the compromised softness and quality in reduced-fat chocolate. It decreases cocoa butter viscosity by mixing within the cocoa butter’s structure and diluting the fat. It also reduces the formation of fat crystals in cocoa butter, decreasing the solid fat content and hardness of the chocolate. Cost is always a concern, too. Taylor notes that “cocoa butter is expensive, so substituting other fats in chocolate is important economically as well as for health reasons. Hence you get combinations of milk fats and cocoa fats, which affect taste and texture.” Manufacturers make particles in the chocolate mixture as large as possible to reduce costs. Smaller particles have a higher surface area and require more fat to coat. On the other hand, larger particles make for less smooth, grittier chocolate, which does not taste as good. Getting the size of the particles right is yet another challenge for researchers. During the manufacture of chocolate, mixtures of different particle sizes clump together tightly leading to thicker fluid and rougher textures. To avoid this, manufacturers use energy-intensive techniques including conching, a process of kneading and stirring at high temperature for many hours in a seashell-shaped vessel. Taylor questions whether the conching process is as efficient as it could be. He studies the flow, or rheology, of molten crumb chocolate using a machine called
Easter 2011
a rheometer that applies a shear stress or strain over time. The most commonly used rheological model for chocolate was originally developed to model the rheology of printing inks. However, after studying chocolate over a wider range of shear stresses, Taylor and fellow chemical engineer Alex Routh recommended a different model. Their new, improved model better describes the properties of crumb chocolate rheology. Routh argues: “if you can understand chocolate structure over time, maybe you can achieve [the same] structure using less energy, and perhaps eventually bypass the conching process.” However, as Taylor highlights “it is not just chocolate, all food manufacturers face the same challenge” of producing lower fat products while maintaining their traditional taste. Therefore, the food industry has entered a new period of research into health and nutrition. Nutritionist Alison Lennox of the Human Nutrition Research (HNR) centre in Cambridge notes that recent years have seen food companies’ research teams increase their interest in nutrition quality. Research at the HNR has provided an understanding of specific nutrients and health implications, but Lennox needs to explain to those who support government initiatives “why you cannot make a low-fat biscuit and still have it taste right.” That is where the scientists are needed. Will food companies have trouble finding talented young minds to do the research? Not likely, if the Cambridge research group is anything to go by. “I have always liked eating chocolate,” explained Taylor, “so researching the stuff seemed like a pretty good idea.” Rachel Berkowitz is a PhD student at the BP Institute in the Department of Earth Sciences
The Challenge of Chocolate 11