Question Corner: What makes chocolate smell musty and mouldy?

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Cocoa beans, when fermented correctly, have a pleasant smell with sweet and floral notes. But they can have an off-putting scent when fermentation goes wrong, or when storage conditions aren’t quite right and microorganisms grow on them. If these beans make their way into the manufacturing process, the final chocolate can smell unpleasant. Researchers had previously used molecular techniques to identify the compounds that contribute to undesirable smoky flavours.

By using gas chromatography in combination with olfactometry and mass spectrometry, researchers at the Technical University of Munich, Germany identified 57 molecules that made up the scent profiles of both normal and musty/mouldy smelling cocoa beans. Of these compounds, four had higher concentrations in off-smelling samples.

The researchers determined that geosmin — associated with mouldy and beetroot odours — and 3-methyl-1H-indole — associated with faecal and mothball odours — are the primary contributors to the musty and mouldy scents of cocoa beans. According to a release from American Chemical Society, they found that geosmin was mostly in the beans’ shells, which are removed during processing, while the latter was primarily in the bean nib that is manufactured into chocolate. The researchers say that measuring the amount of these compounds within cocoa beans could be an objective way to detect off-putting scents and flavours.

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Printable version | Jun 15, 2021 6:59:01 PM |

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