Physicists deploy 3D printing in search of the world’s crunchiest chocolate

A team of Dutch scientists have taken on the grueling task of designing the perfect piece of chocolate, using new 3D printing techniques to create designs that snap in the sweetest way when bitten. Obviously, extensive testing is needed.

Some of us pagans are content to simply shovel handfuls of supermarket-grade chocolates into our mouths and ogle with brown teeth at our offspring. For others, chocolate is a pleasure to be taken very seriously. There are chocolate tasting classes where people can explore the intricacies of flavor, texture, mouthfeel, and melting, ruining M&Ms for themselves forever.

An expert chocolatier must act a bit like a blacksmith, heating and cooling their emulsion with precision to select the perfect crystal lattice structure formation – cocoa butter, as physicist and chocolate shop owner Richard Tango puts it. -Lowy at Chemistry World, “is a polymorphic crystal.” Phase V is the most desirable – it cracks and melts rather than crumbles, and gives premium chocolates their deliciously shiny sheen. But it can take weeks for a properly tempered piece of chocolate to fully crystallize, and moreover, phase V crystals are unstable and tend to degrade into dull phase IV crystals over time.

This is just to illustrate that a ton of thought and expertise, and quite a bit of science, goes into every step of making premium candy. It should therefore come as no surprise to learn that it has caught the attention of specialists in metamaterials and 3D printing at the University of Amsterdam, who have just published an article in the journal soft material on their exploration of the perfect structures for optimal chocolate mouthfeel.

Spiral designs offer a promising ability to adjust and optimize bite “fracture events”

University of Amsterdam

They left with a reasonable idea in mind: that most people enjoy the experience of the crunch of chocolate when biting into it, and the more crunches the better. They started trying to design shapes that would maximize these “fracture events”, finding that the spiral shapes offered many opportunities to design and adjust the cracking points, depending on the direction of the bite.

They put a series of drawings in front of a “very willing” test panel and took audio recordings of people biting into each drawing. Sure enough, they found that a greater number of spiral wraps produced an audibly higher number of crackle events, and they confirmed that test participants were able to distinguish between the more cracked designs and least cracked, and yes, “the overall sensory score, as well as the perceived number of cracks, exhibit a positive correlation with the number of cracks measured from the force-displacement curve.”

They then began experimenting with “maximum anisotropy structures” – designs that are strong if bitten in one direction, but brittle and cracked in another, offering a range of other interesting patterns.

An anisotropic study, attempting to design chocolates that are super strong with force applied to one axis, and super cracked when applied to another
An anisotropic study, attempting to design chocolates that are super strong with force applied to one axis, and super cracked when applied to another

University of Amsterdam

In order to create these research-grade chocolates, the team had to run this notoriously difficult material in a 3D printer while ensuring it was properly tempered to maximize the formation of these precious Phase V crystals. To do this , they heated the chocolate to 45°C (113°F) to destroy all of its crystals, then allowed it to cool, adding solid pellets of pre-tempered chocolate to form phase V “seeding” crystals, until it drops below 34°C (93°F), the melting point of phase V crystals.

At this point, they loaded the chocolate into syringes and placed them in cartridges for a 3D biotracer, which were stored at 32°C (90°F). Then they printed their shapes, layer by layer, on a printing base kept at 12°C (54°F), with a fan circulating air to encourage the chocolate to solidify as quickly as possible, ready for the next layer.

They got in trouble; the chocolate began to crystallize in the syringe tube, so the machine had to be constantly recalibrated as the thickness of the printed lines changed. It also thickened as it printed, requiring significant pressure and speed adjustments as each print progressed, and each time a line stopped or started it there were inconsistent drops of chocolate left on the nozzle, further complicating any attempt at complete consistency between samples.

So while the team has made progress in discovering which chocolate models are the most interesting, the crunchiest and the most enjoyable to eat, there is clearly still a lot of work to be done to design a 3D printing system capable of reliably manufacture the high quality tempered chocolate models.

The article was published in the journal Soft Matter.

Watch a short video below.

Amsterdam Science & Innovation Award pre-finalist Corentin Coulais

Source: University of Amsterdam

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