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Regarding the treatment of coffee beans, longer fermentation times can give a better taste, contrary to popular belief. Lactic acid bacteria play an important positive role in this process. Other species of microbes may also play a role in this process, but additional research is needed to better understand their role. The research is published on February 1 in Applied and environmental microbiology.
"A cup of coffee is the end product of a complex chain of operations: farming, post-harvest processing, roasting and brewing," said lead researcher Luc De Vuyst, M.Sc., Ph.D. ., professor of industrial microbiology. and food biotechnology, Vrije Universiteit Brussel, Brussels, Belgium. "There are several variants of post-harvest treatment, of which wet processing and dry treatment are the most common." The wet treatment – commonly used for Arabica and specialty coffees – is the stage that includes fermentation.
"We conducted research at an experimental farm in Ecuador using a multiphase approach that included microbiological, metabolomic and sensory badyzes," said Dr. De Vuyst.
Fermentation was of particular importance. During a prolonged fermentation, leuconostocs – a kind of lactic acid bacteria used in cabbage fermentation in sauerkraut and leavened sourdough – declined in favor of lactobacilli, said Dr. De Vuyst. Lactic acid bacteria were already present before fermentation and these acid-tolerant lactobacilli proliferated even more during this process.
However, it is difficult to establish a causal link between the microbiota and the volatile compounds present in the grains – the compounds that contribute to the smell of coffee – since many of these compounds can be disrupted. microbial, endogenous or chemical origin, "said Dr. De Vuyst.
"However, we have seen the impact of microbial communities, particularly lactic acid bacteria," said Dr. De Vuyst. They have given fruity notes and may have "had a protective effect on coffee quality during fermentation because of their acidification of the fermenting mbad, providing a stable microbial environment and thus preventing the growth of undesirable microorganisms that lead to often with undesirable aromas ". he said.
"In addition, there is an accumulation of fermentation-related metabolites on the coffee beans, which affects the quality of the green coffee beans and thus the sensory quality of the coffees so prepared," said Dr. De Vuyst.
Dr. De Vuyst pointed out that the influence of each stage of treatment on the taste of coffee remains mostly unknown. "We were aware of the presence of many microorganisms during coffee fermentation in humid environments: enterobacteria, lactic acid bacteria, yeasts, acetic bacteria, bacilli and filamentous fungi," said Dr. De Vuyst, but we do not know again how most bacteria influence this process.
The work was a collaboration between the Vrije Universiteit Brussel and the Nestlé research center. "Nestlé was interested in the fundamentals of coffee processing, especially the post-harvest processing chain, to correlate it with the roasting process and of course the quality of the final cup," said Dr. De Vuyst .
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