Little-known fact: the things we like about chocolate – its creamy smooth texture and how it melts in our mouths – are thanks to the crystal structure of cocoa butter.
Now University of Guelph researchers say they have found a way to create that perfect crystal structure while simplifying the fussy tempering process of repeatedly heating and cooling chocolate while mixing.
“Cocoa butter has a complicated crystallization behaviour,” says food scientist Alejandro Marangoni. “It has six crystal forms and you have to lead it through the whole crystallization process to get the fifth form that has the correct polymorphism.”
The problem is that the fifth form is harder to achieve and maintain than the others. This means it’s not an easy thing to temper chocolate to a point where it is glossy, melts sharply in your mouth, releases flavour and snaps perfectly when broken.
Tempering is a precise, time-consuming process in which chocolate makers slowly heat and cool melted chocolate repeatedly to coax the triacylglycerol molecules in the cocoa butter to crystallize into a stable fifth form.
The process involves “seeding” to encourage the chocolate to properly crystallize. The “seed” is usually bits of already-tempered chocolate that provide a surface upon which the still-liquid triacylglycerol molecules can crystallize.
A good chocolatier can usually do this by eye. They shear the chocolate on a cold marble slab to induce nucleation, and then scoop it into a warm bucket to melt away the meta-stable crystal forms so that just the fifth form remains.
“But that can’t be done in large-scale chocolate manufacturing,” says Marangoni.
Instead, chocolate manufacturers use industrial tempering units, often up to three storeys high. But the units aren’t foolproof either, and there can be large variabilities between batches of cocoa butter.
Marangoni and his team – research associate Dr. Saeed Ghazani, former chemistry student Jay Chen and master of science student Jarvis Stobbs – suspected they might use one of the “minor components” naturally present in cocoa butter to seed the fifth crystal form without the need for the full tempering process.
As Marangoni explains, about 30% of chocolate is cocoa butter, composed of triacylglycerols. Less than 3% is composed of minor components: non-triacylglycerol lipids, such as monoacylglycerols, diacylglycerols, free fatty acids, diacylglycerols, free fatty acids and phospholipids.
What little research there has been into these minor lipid components suggests that some can inhibit crystal growth while others can encourage it. The team figured phospholipids were a good place to start because, as previous research showed, cocoa butter seed crystals contain a significantly greater proportion of phospholipids.
This could be because phospholipids are amphipathic molecules and so may play a role in the nucleation process of cocoa butter triacylglycerols, says Chen, who is now a medical student at McMaster University. Phospholipids might self-assemble into mesomorphic structures that provide a surface upon which triacylglycerols can nucleate and grow.
The team’s research, published in August in Nature Communications, showed that adding the phospholipid to melted chocolate and then rapidly cooling it once to 20C accelerated crystallization without the need for tempering. The resulting chocolate had an optimal microstructure, with the ideal surface gloss, melting point and strength.
“We didn’t fully come up with a mechanism for why this particular phospholipid worked well,” says Chen. “We also tested another phospholipid, and it had some degree of success, but it wasn’t perfect.”
Still, the researchers were able to confirm their finding with help from the Canadian Light Source at the University of Saskatchewan. The facility’s synchrotron allowed the team to get micrograph images of the interior microstructure of their chocolate and confirm the positive effect their ingredient had on the chocolate structure.
It was a particularly sweet project for Chen: “I love chocolate,” he says. “It’s the whole reason I decided to get involved in this research. Professor Marangoni has so many projects, but I said this was the one I wanted to work on.”