« Tuning Chocolate Flavor Through Yeast Research »-Science Daily

« The yeasts used to ferment cocoa during chocolate production can modify the aroma of the resulting chocolate, research shows. The investigators noted striking differences in aroma among the chocolates made from fermentations using different robust yeasts. »

« Researchers of Leuven University and VIB in Belgium have shown that the yeasts used to ferment cocoa during chocolate production can modify the aroma of the resulting chocolate. « 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 » says Dr. Jan Steensels, one of the lead researchers involved in the project. The results were published November 20 in Applied and Environmental Microbiology, a publication of the American Society for Microbiology

Looking for robust yeast strains for chocolate production

Initially the researchers sought robust yeast strains that could outcompete the many invading yeast strains that flood the cocoa beans during fermentation. « 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. The beans are surrounded by a gooey pulp, which is fermented by yeasts and bacteria. Any species in the environment can get into the mix, leaving little control over the ultimate flavor. But by outcompeting other microbes, robust yeast strains could prevent such infelicitous variability in taste. » Says Esther Meersman who carried out much of the field trials in a cocoa farm in Malaysia. (…) »

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Esther Meersman, Jan Steensels, Nore Struyf, Tinneke Paulus, Veerle Saels, Melissa Mathawan, Leen Allegaert, Gino Vrancken, Kevin J. Verstrepen. Tuning chocolate flavor through development of thermotolerantSaccharomyces cerevisiaestarter cultures with increased acetate ester production. Applied and Environmental Microbiology, 2015; AEM.02556-15 DOI: 10.1128/AEM.02556-15

Abstract :
« Microbial starter cultures have been extensively used to enhance the consistency and efficiency of industrial fermentations. Despite the advantages of such controlled fermentations, the fermentation involved in the production of chocolate still is a spontaneous process that relies on the natural microbiota at the cocoa farms. However, recent studies indicate that certain thermotolerant Saccharomyces cerevisiae cultures can be used as starter cultures for cocoa pulp fermentation. In this study, we investigate the potential of specifically developed starter cultures to modulate the chocolate aroma. Specifically, we developed several new S. cerevisiae hybrids that combine thermotolerance and efficient cocoa pulp fermentation with a high production of volatile flavor-active esters. In addition, we also investigated the potential of two species (Pichia kluyveri and Cyberlindnera fabianii) that produce very large amounts of fruity esters. GC-MS analysis of the cocoa liquor revealed an increased concentration of various flavor-active esters and a decrease in spoilage-related off-flavors in batches inoculated with S. cerevisiae starter cultures, and, to a lesser extent, in batches inoculated with P. kluyveri and C. fabianii. Additionally, GC-MS analysis of chocolate samples revealed that whilst most short-chain esters evaporated during conching, longer, more fat-soluble ethyl and acetate esters such as ethyl octanoate, phenylethyl acetate, ethyl phenylacetate, ethyl decanoate and ethyl dodecanoate remained almost unaffected. Sensory analysis by an expert panel confirmed significant differences in the aroma of chocolates produced with different starter cultures. Together, these results show that selection of different yeast cultures opens novel avenues to modulate chocolate flavor. »

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