Chocolate lovers may soon find themselves choosing flavors from a range rivaling that of wine and tea, conclude researchers who show changing the yeast used in the first stage of chocolate production – the fermentation of cocoa pulp – can alter its flavor.

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After harvesting, the cocoa beans are piled in large heaps – seen here covered with banana leaves – where the pulp surrounding them begins to ferment.
Image credit: KU Leuven

The researchers, from Leuven University and the biotechnology company VIB, both in Belgium, report their findings in the journal Applied and Environmental Microbiology.

Dr. Jan Steensels, one of the lead researchers, says:

“The set of new yeast variants that we generated makes it possible to create a whole range of boutique chocolates to match everyone’s favorite flavor, similar to wines, tea and coffee.”

The shelf of the supermarket or grocery store marks the final destination of the fascinating journey chocolate makes from its origin as the seeds of the cacao or chocolate tree to consumer product.

First author and PhD student Esther Meersman is intimately familiar with the start of this journey – she conducted many of the field trials for the study on a cocoa farm in Malaysia. She describes what happens when the cocoa beans are harvested:

After harvesting, the cocoa beans are collected in large plastic boxes, or even piled in large heaps on the soil, right in the farms where they are grown.”

While the cocoa beans are in the heap for several days, naturally present yeasts and bacteria ferment the gooey pulp surrounding the beans before they are dried and roasted.

“Any species in the environment can get into the mix,” Meersman says of the yeasts, “leaving little control over the ultimate flavor.”

But a small range of robust yeast strains outcompetes the wide variety of microbes present, thus ensuring there is no “infelicitous variability in taste,” she adds.

The researchers wondered if the huge expertise and knowledge about yeast and fermentation that has accumulated over centuries of brewing wine and beer could be applied to the cocoa pulp fermentation to introduce a wider, more controlled, variety of natural flavors.

The first step was to breed robust yeast strains that could be introduced at the start of the cocoa pulp fermentation that could outcompete the already present yeast strains that naturally invade the cocoa beans while they are in the heap.

For this part of the study, they teamed up with researchers from one of the world’s largest cocoa producers, Barry Callebaut, with headquarters in Switzerland. They set out to find yeast strains that met two requirements: they had to outcompete other strains, and they had to produce a good flavor.

The team found they could produce some strikingly different flavors in chocolate just by fermenting the cocoa pulp with different robust yeasts – they did not have to vary the method or the recipe, just the yeast.

They bred several new yeast hybrids that combine robustness with strong flavor production. Meersam says at first they were surprised that the volatile aroma compounds survived the drying and roasting stage of the beans, but she then explains:

“We think that the volatiles are protected from evaporation since they are dissolved in the fat fraction.”

Senior author Kevin Verstrepen, a professor who heads a lab that specializes – among other things – in industrial fermentation, concludes:

This means that for the first time, chocolate makers have a broad portfolio of different yeast strains that are all producing different flavors. This is similar to the current situation in beer brewing and wine making.”

Every week it seems that a report comes out suggesting the harms of eating chocolate outweigh the benefits, or the other way around. For a review of some of these pros and cons, see the Medical News Today knowledge article Chocolate: health benefits, precautions.