Belgian researchers working in collaboration with the world's largest chocolate producer, Barry Callebaut, have bred robust yeasts that ferment cocoa to produce bespoke aromas and flavors in the finished chocolate. According to the team, this makes possible a new range of boutique chocolates that can match particular flavors in the same way that craft beer, coffee, tea, and wine can.

Chocolate may be most familiar to us as rich, brown bars or thick syrups, but it starts out as unappetizing cocoa bean pods. After harvesting, these are split open to reveal the beans themselves surrounded by a sticky white pulp, which are scooped out of the skin. These are placed in large plastic boxes or left in heaps, where native yeasts cause them to begin to ferment in the tropical heat in much the same way as the yeast on the skins of grapes start wine fermentation. As the cocoa ferments, it kills the beans, so they can't germinate, and flavor precursors form. After about a week, the beans are then dried before being sent off for roasting and further processing into chocolate.

It's a centuries old process, but the research team says that it's a bit haphazard as all sorts of wild yeasts and bacteria compete to see who will dominate in the cocoa fermentation eco-system. What the team first hoped to do was to find robust strains of yeast that would quickly dominate the others, allowing cocoa producers better control over the chocolate's taste.

It turned out that the different robust strains produced markedly different flavors and aromas. This was despite the fact that the recipe and fermentation process for each one was identical. The team then began to breed the yeast strains and created new hybrids that formed strong flavors that were retained in the final product instead of evaporating – possibly due to the flavor-bearing volatile chemicals being trapped in the fat.

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

The research was published in Applied and Environmental Microbiology.