A mix of unripe, ripe and over-ripe coffee cherries after harvesting, prior to post-harvest processing. Daily Coffee News photo by Nick Brown.
New research from Brazil suggests that highly controlled anaerobic fermentation can improve the quality of unripe coffees to the point that they meet specialty coffee standards.
Published in the Springer Nature journal Food and Bioprocess Technology, the study outlines a post-harvest production pathway through which coffee farmers may add more value to coffees that were picked prematurely and might otherwise fetch lower prices through conventional local markets.
The picking of under-ripe cherries is an especially persistent concern in Brazil, the world’s largest coffee-producing country, where large plantation farms typically employ mechanized picking processes, as opposed to hand-picking.
“Contrary to the conventional view that immature beans are detrimental to coffee quality, results revealed that, under controlled fermentation conditions, immature beans can enhance the sensory characteristics of the beverage, resulting in profiles comparable to or even superior to those of coffees made exclusively from mature beans,” the study states.
The team at Brazil’s Federal University of Uberlândia employed what they called self-induced anaerobic fermentation (SIAF) to a relatively new arabica cultivar called Arara, which was bred for disease-resistance by the Brazilian agency Procafé and launched in 2012.
The research team placed ripe and unripe fruits in bioreactors — 200-liter polystyrene barrels that were hermetically sealed — for up to 96 hours after harvesting. No oxygen entered the bioreactors, and carbon dioxide was released through a valve. In some experiments, inoculants chosen specifically for coffee fermentation were added to the mix.
“With this work, we saw that using SIAF at different fermentation times, with temperature and pH control and with or without the addition of inoculum, can not only minimize the deleterious effects of immature beans on the beverage, but also make it superior,” study lead author Luiza Braga said in an announcement of the publication.
While the authors called for additional research to pinpoint the compounds responsible for quality gains, plus research into other cultivars, the findings offer a potential tool for producers seeking to improve quality scores and command higher prices when dealing with large-scale, time-bound harvests.
“Coffee growers and experts have been seeking knowledge about the process because of the gain in flavor and aroma it brings to the drink, which can then fetch higher prices than those usually found on the market,” said Federal University of Uberlândia professor and study coordinator Líbia Diniz Santos.
The research was funded by grants from the São Paulo Research Foundation (FAPESP) and the Minas Gerais Research Foundation (FAPEMIG), with support from multiple other Brazilian institutions. The authors did not declare any competing interests.
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