Think about biting into a piece of chocolate. What makes it enjoyable? Is it the sweetness? The way it melts in your mouth? The crunch? The sound it makes? All of the above?
A team at the University of Amsterdam is attempting to use physics and geometry to answer some of these questions, and to—hopefully—create an even more enjoyable treat. Their result, a spiral-shaped 3-D printed candy, doesn’t look like anything currently on the supermarket shelf. But it may just be the future of food.
“There wasn’t anyone on the team who didn’t like chocolate, fortunately,” says Corentin Coulais, a physicist at the University of Amsterdam who led the research, laughing.
Coulais normally works with non-food “metamaterials”—materials with structures and properties not found in nature. In the past, his work has involved shape-changing materials with applications for robotics, prosthetic limbs and electronics. But a partnership with the food and consumer goods giant Unilever had him and his team turning their minds to chocolate.
First, the researchers tempered dark chocolate containing 72 percent cacao—heating and cooling it carefully to give it a stable structure. Then they printed the chocolate into a series of spiral shapes using a 3-D printer. Some of the spirals were simple s-shapes, while others were more intricate, almost like labyrinths.
The team then submitted the chocolates to a series of mechanical tests to see how they would break when “bitten.” When the chocolates were pressed from above, they shattered into many pieces (especially the more elaborately spiraled ones). When bitten from the side, they usually cracked only once.
Why does this matter? Well, the next step of the research, published last month in the journal Soft Matter, involved giving the chocolates to a very lucky panel of human testers. The investigators asked which shapes the testers preferred and why.
“The more intricate the shape, the more crack it had, and the more they seemed to enjoy it,” Coulais says.
This fact that testers enjoyed the more brittle chocolate was not surprising. Previous research has shown that people enjoy the sensation of food crunching or breaking in their mouths. They especially enjoy hearing the shattering sounds; taste researcher Alan Hirsch describes it as the “music of mastication.” Some scientists think this may be because crunchiness is a signal of freshness—think fresh apples versus wilted cabbage—and that texture helped our ancestors seek out the most nourishing foods.
Chocolate, of course, is not famous for being healthy. But the research is part of the broader field of “edible metamaterials,” which has potential for creating foods that are more nutritious, easier to eat, or better for the environment.
There are “exciting times ahead in the development of ‘metafoods,’” says Fabio Valoppi, a researcher at the University of Helsinki who studies edible metamaterials. The field is young, Valoppi says, but it’s full of promise.
Valoppi mentions recent research on morphing pasta, or geometrically engineered pasta that goes from flat to 3-D during cooking. “You can imagine that having such a type of pasta can help reduce our ecological footprint by reducing emissions and transportation costs,” he says. “Flat pasta can be stacked more efficiently in a package, and having it morphing during cooking will allow us to eat them with the shapes we love the most.”
Using geometry to tailor a food’s mouthfeel could allow researchers to use healthy foods with low carbon footprints (think lentils or tofu) to create interesting, palatable meat substitutes, says Coulais. The same techniques could create special foods for people who have trouble with biting or chewing because of illness or dental issues. If you could control how much force is needed to shatter a piece of food, you could make tasty solid foods that are extremely easy to bite.
“People who could not chew well could still have an interesting [eating] experience,” Coulais says.
More futuristically, Coulais imagines a world where geometry is a tool for individualized food preparation. Imagine astronauts on the International Space Station printing out foods tailored to their needs and preferences, or soldiers dining on MREs that use edible metamaterials to deliver maximum calories in a minimum amount of space.
Even more sci-fi is the idea of edible holograms—foods whose surfaces have been etched in such a way to give them shiny holographic designs. This changes the color of the food (imagine candy with no artificial colorants) and could potentially lead to edible nutritional labeling. “This can reduce the need for printing labels, and the food product becomes the label itself,” Valoppi says.
The research into the geometry of shattering also has non-food applications. Figuring out how to control where a material breaks could mean designing better crash helmets or other protective gear. Controlled shattering could even mean safer planes or cars. Imagine a vehicle designed to have an exterior that shattered in a way that protected the interior.
Coulais does hope to continue his research on foods. He’s currently working on building a consortium with food companies, to use his geometric modeling on food development. The possibilities are almost limitless.
“Because metamaterials are still in their infancy, there is great potential in this field,” Valoppi agrees. “On Earth, we have limited materials with limited properties. The beauty of metamaterials—in both their edible and non-edible forms—is that by just adding some shapes and architecture to the same materials that have limited properties, we can give them new functionalities.”