Fermentation process turns unripe coffee beans into high-scoring specialty drinks

In the selection of specialized cafes, those which obtain a score of more than 80 points in the blind tests are free from physical and sensory defects. The greenish beans are known to give the drink an astringent taste, which is described as hard, spicy and dry. These beans are therefore thrown, as well as broken, black, burned, stung or undersized beans.

However, in a study published in the journal Food and bioprocedian technologyResearchers from the Federal University of Uberlândia (UFU) of Patos de Minas (State of Minas Gerais, Brazil) led a series of fermentations with ripe and non -ripe fruits of the Arabic cultivar of the Arabica café (Coffea Arabica).

Consequently, they obtained comparable drinks and even superior to those prepared with beans from ripe fruits, according to all the protocols of the Specialty Coffee Association (SCA), an international organization which establishes standards for specialized cafes.

In the blind cut tests, which assess coffee according to its sensory attributes, professional tasters (called Q Q) gave drinks containing a percentage of non -ripe fruit scores greater than 80, which defines specialized coffee.

The researchers obtained these results using self -induced anaerobic fermentation (SIAF), in which the fruits are placed in bioreactors – 200 liter polystyrene barrels which are hermetically sealed – up to 96 hours after harvest. No oxygen enters bioreactors and carbon dioxide is released by a valve.

Microorganisms naturally present in coffee fruit then make a series of biochemical processes which result in a distinctive coffee flavor. In some experiences, inoculants – specific microorganisms previously isolated for this purpose – have been added to this type of fermentation.

“With this work, we have seen that the use of SIAF at different fermentation times, with the temperature and the control of the pH and with or without adding the inoculum, can not only minimize the deleterious effects of the farm,” explains Luiza Braga, adding value during its control degree in the graduate program of the graduate products program within the Facest Face Patos of Minas.

“Anaerobic fermentation, carried out immediately after harvesting and before drying, is not a traditional process. However, coffee producers and experts have sought knowledge on the process due to the gain of the flavor and aroma it brings to the drink, which can then recover higher prices than those generally found on the market,” said Líbia Diniz Santos, a teacher and coordinator the study.

The Arara cultivar was launched in 2012 by the Procafé Foundation after 15 years of research looking for a coffee resistant to diseases adapted to the various climatic conditions of the Cerrado Savanne Biome of Brazil. The drink is evaluated for its citrus notes and its robust body, which makes it attractive for domestic and export markets.

The study authors used an artificial intelligence tool developed by the research group and noted that 70% of the fruits used in experiences, which were collected in Fazenda Chuá in Patos de Minas, were immature.

Despite the use of green beans in drinks tasted by panelists, the authors point out that the other SCA criteria have been strictly followed. Thus, broken and small beans were thrown during the preparation. Consequently, green beans represented 13% to 30% of the total drink.

“We believe that if there had been 70% green beans in the drink, even if they were fermented, it would have been perceptible in the final product,” said Santos.

In total, 32 treatments have been tested, including different fermentation times ranging from 24 to 96 hours with and without temperature control. The combinations also included the presence or absence of inoculum, as well as submerged fermentation with 30% of the bioreactor filled with water or fermentation in the solid state without water.

The group has developed an electronic device that monitors the pH and the temperature and transmits the sensor data inside the bioreactor to an external monitor. This eliminates the need to open the barrel and interfere with experience in order to collect information.

“When we checked the external temperature at 27 ° C, we observed that the scores were higher, even higher than those of preparations containing only ripe grains. With this, we can demonstrate that anaerobic fermentation, in particular in solid state, adds sensory attributes that increase coffee to the special category,” explains Braga.

The group now intends to understand which compounds or compounds generated in the fermented green grain provide the sensory attributes that give coffee its special qualities. Future work will also explore the effect of anaerobic fermentation on other coffee varieties.