Chocolate Flavours Unlocked by Yeast: A Sweet Story!

(December 21st, 2015) It’s the most wonderful time of the year, especially for chocolate lovers. A delicious study by Belgian scientists revealed that yeast strains involved in cocoa bean fermentation can modulate the resulting chocolate’s flavour, unlocking a whole new world of chocolate aromas!

Yes, that same heady chocolate-y aroma that causes hearts to melt and mouths to water. With Christmas right around the corner, chocolate sales everywhere are skyrocketing and going through the roof. Simply put, chocolate makes for the perfect gift. Now who doesn’t enjoy this delightful concoction that can be savoured by both young and the old, be drunk as a comforting beverage, baked into decadent cakes and cookies or just eaten as a simple bar of melt-in-your-mouth goodness. With all the versatile roles that chocolate takes in its stride and the mind-boggling variety that is available to us today, one could easily believe that we’ve finally exhausted all the options that chocolate has to offer to us.

Well, do not be perturbed, it might only be the beginning. Belgian researchers (from Leuven University and VIB) have recently discovered that it is possible to tune or regulate the aroma of chocolate. This aroma is shaped very early in the process of chocolate production, right at the farm when the cocoa beans are harvested. Post harvesting, the beans are usually collected in large containers or piled up on the farmland. At this stage, local yeast and bacterial strains get access to the gooey pulp that the cocoa beans are encased in, and set about fermenting it and giving shape to the chocolate aroma.

As one would imagine, this unsupervised inoculation and subsequent fermentation leaves much to chance. Since any microbial species can dominate this mixture, chocolate makers have no real control over the flavour and aroma of the resulting chocolate. Especially microbiota that produce weak or undesirable flavours in the chocolate, prove to be a major setback to the entire process.

To address this issue, the scientists, led by Kevin Verstrepen, developed robust and efficient starter cultures. The idea was to generate yeast strains (Saccharomyces cerevisiae) that would dominate the cocoa bean fermentation and keep invading, less desirable microbiota at bay. This was achieved by generating single yeast hybrids that were thermo-tolerant and hence more robust. Furthermore, these strains were very efficient at the flavourful fermentation of the cocoa bean pulp via ester production. The research team also looked at two other strains (Pichia kluyveri and Cyberlindnera fabianii) that yield ample amounts of fruity esters during fermentation.

The robust yeast starter cultures were then put to work in fermenting the cocoa beans. The resulting cocoa liquor was analysed via gas chromatography mass spectrometry. As expected by the team, it “revealed an increased concentration of various flavor-active esters and a decrease in spoilage-related off-flavors”, elegantly confirming that the robust strains had done their job. Additionally, a lot of this flavour came from “longer, more fat-soluble ethyl and acetate esters”. Although these esters are volatile compounds, they are believed to escape evaporation during drying and roasting as they are dissolved in the fat fraction of the beans.

Moreover, the identical fermentation process using different starter cultures resulted in aromatically distinct chocolate aromas. “Sensory analysis by an expert panel confirmed significant differences in the aroma of chocolates produced with different starter cultures”. This is quite similar to the ‘controlled’ fermentations of wine making or beer brewing, where the starter microbial strains characteristically influence the flavour, aroma and taste of the end product. For the chocolate industry, these results open up whole new vistas for the creation of chocolate flavours. The set of new yeast variants would make it possible to develop flavours to please virtually every palate on earth. The possibilities seem truly endless!

Sweetly enough, this research originates from Belgium, a country whose long association with chocolate goes back to the 17th century. Belgians take their chocolate very seriously as can be seen by the fact that the constitution of Belgian chocolate has been regulated by law since 1884!

So when you bite into a praline this Christmas (pralines being a Belgian invention), remember that the best in chocolate is yet to come. On this rather sweet and happy note, may the festive season bring you and your loved ones a lot of happiness and good cheer! A very merry Christmas and a very happy New Year!

Latika Bhonsle

Photo: Kratochvil

Last Changes: 01.26.2016