How Microbes Help Make a Perfect Cup of Coffee

Ever wondered what makes your coffee taste good? It's the microbes, finds a study.

The study showed that lactic acid bacteria which help in the longer fermentation of coffee beans results in better taste, contrary to conventional wisdom.

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

There are several variants of post-harvest processing, among which wet processing and dry processing are the most common. Wet processing - commonly used for Arabica and specialty coffees - is the step that includes fermentation.

The research, published in the Applied and Environmental Microbiology journal, was carried out at an experimental farm in Ecuador. The team found that during extended fermentation, leuconostocs - a genus of lactic acid bacteria used in the fermentation of cabbage to sauerkraut and in sourdough starters - declined in favour of lactobacilli.

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

"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," De Vuyst said.

But De Vuyst noted that the microbial communities, in particular the lactic acid bacteria, showed an impact.

It 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.

Besides lactic acid bacteria, other micro-organisms that play a role during wet coffee fermentation include enterobacteria, yeasts, acetic acid bacteria, bacilli and filamentous fungi. But it is still not known how most bacteria influence this process, De Vuyst said.