In a recent paper published in the journal Soft Matter, a team of Dutch scientists described how 3D printing could create the crispiest chocolate possible. Although everyone tastes chocolate differently, the material actually has quite unique and subtle flavors and textures. Even chocolate experts must control the heating and cooling process with the precision of a blacksmith to form the perfect lattice structure of cocoa butter.
In an interview with Chemistry World, Richard Tango-Lowy, a physicist and chocolate-shop owner, referred to the hexagonal polycrystalline form. It melts when it crackles, rather than shattering, and gives high-end chocolate a pleasant sheen.
Such a properly warmed chocolate, however, can take weeks to make. Not to mention that the V-phase crystal itself is not very stable and easily degrades to the dull IV phase crystal over time.
In the pursuit of this superior taste, metamaterials and 3D printing experts from the University of Amsterdam have come to some very deep and detailed conclusions. The research was based on the reasonable assumption that most people like the sound of chocolate crackling, and the more the better.
They then set about trying to design a chocolate shape that maximizes these "fracture events," and found that the spiral has ample opportunity to design and adjust the point of the crack, depending on the direction of your lower mouth (bite).
By placing a series of shape designs on the test board, and recording the sound of each person's bite. Not surprisingly, the more spiral windings produced more audible crackling, and test participants were able to distinguish between them.
In summary, the overall sensory rating of the chocolate -- such as the number of perceived cracks -- was positively correlated with the number of cracks measured by the force-displacement curve.
They then set about trying to maximise this anisotropic structure -- devising a series of other interesting patterns that were relatively strong in one direction, but more brittle and prone to cracking in another.
It is said that in order to make the chocolate needed for the study, the team had to use a 3D printer to complete the material preparation for this spacing. Also make sure the chocolate is properly tempered to maximize the formation of these precious V-phase crystals.
The chocolate was heated to 45 °C(113 °F) to destroy all crystals, then cooled to add pre-conditioned solid particles to sow conditions favorable for V-phase crystal formation, until cooled to 34 °C(93 °F), which is also the melting point of V-phase crystals.
At this point, the chocolate is placed in a container at 32 ° C (90 ° F) and the shape is printed layer by layer onto a base plate at 12 ° C (54 ° F). In preparation for the next layer of printing, a fan circulates air to help the chocolate set as quickly as possible.
But it's not all plain sailing. Chocolate crystallizes easily in pipes, for example. As the thickness of the print line changes, the machine must be recalibrated again and again. And it thickens as the print progresses, requiring major adjustments to pressure and speed each time.
Not to mention the inconsistent droplets of chocolate left on the nozzle each time it was turned on and off, further complicating any attempt to control sample uniformity.
