Microbes help make coffee tastier

Certain microbes could make your cup of coffee tastier, say scientists who found that longer fermentation process lends a better taste.

The research, published in the journal Applied and Environmental Microbiology, showed that lactic acid bacteria play an important, positive role in processing coffee beans.

“A cup of coffee is the final product of a complex chain of operations: farming, post-harvest processing, roasting, and brewing,” said Luc De Vuyst, a professor at Vrije Universiteit Brussel in Belgium.

“There are several variants of post-harvest processing, among which wet processing and dry processing are the most common,” said De Vuyst.

Wet processing — commonly used for Arabica and specialty coffees — is the step that includes fermentation.

“We carried out the research at an experimental farm in Ecuador through a multiphasic approach, encompassing microbiological, metabolomics, and sensory analysis,” said De Vuyst.

Fermentation was of particular importance. During extended fermentation, leuconostocs — a genus of lactic acid bacteria used in the fermentation of cabbage to sauerkraut and in sourdough starters — declined in favor of lactobacilli, he said.

Lactic acid bacteria were already present before fermentation, and these acid tolerant lactobacilli proliferated even more during this process.

However, it is challenging to draw a causal link between the microbiota and the volatile compounds in the beans — those compounds that contribute to the coffee’s smell — since many of these compounds can be of microbial, endogenous bean metabolism, or chemical origin,” said De Vuyst.

“However, we did see an impact of the microbial communities, in particular the lactic acid bacteria,” he said.

They yielded fruity notes, and may have “had a protective effect toward coffee quality during fermentation because of their acidification of the fermenting mass, providing a stable microbial environment and hence preventing growth of undesirable micro-organisms that often lead to off-flavours,” he said.

“Furthermore, there is a build-up of the fermentation-related metabolites onto the coffee beans, which affects the quality of the green coffee beans and hence the sensory quality of the coffees brewed therefrom,” said De Vuyst.

De Vuyst emphasised that how each stage of processing influences the taste of coffee remains mostly uncharted.

“We were aware of many different micro-organisms during wet coffee fermentation — enterobacteria, lactic acid bacteria, yeasts, acetic acid bacteria, bacilli, and filamentous fungi,” said De Vuyst, but it is still unknown how most bacteria influence this process.