Green coffee beans – new processing methods

Common Knowledge (Written: Taki Tiến Nguyễn)


15:04 13/09/2022

CFRR – Coffee comes from a fruit tree, besides the traditional methods, coffee makers have created some new processing methods to create richer flavors for coffee.

The coffee berries have consisted of the outer skin, pulp, mucilage, husk, the silk-the the last layer surrounding the two inner seeds. However, many of the attractive flavors come from the fruit pulp and mucilage rather than the seeds, so the processing is to remove these layers but still get the essence, then dry to an optimal level. There are many ways to remove layers and these methods will affect the flavor of the final coffee product.

Anaerobic processing method

Anaerobic is an anaerobic fermentation method that has become quite popular for specialty coffee at present, anaerobic fermentation is almost a wet processing yet anaerobic means the process that fermentation is carried out in completely sealed and oxygen-free tanks. The coffee flavors that are complex, unexpected, and wild increasingly popular in Central American countries such as Costa Rica and Honduras. Ripe coffee berries are harvested and put into a separator to divide the seeds and other parts of the fruit from each other, then carry out anaerobic fermentation. Anaerobic fermentation is the process by which chemicals especially carbohydrates such as sugar are broken down into alcohols or acids produced from microorganisms in the absence of oxygen. 

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The flavor of Anaerobic fermented coffee is always evaluated uniquely.
Photo: mtpak

There are two ways to do this anaerobic fermentation:

  • One is: Put the coffee in the tank and inject carbon dioxide (CO2) to completely remove oxygen, which was explained that there was no oxygen the first time, so it was carried out anaerobically, this process takes about 20 hours.
  • Second: Put the coffee into a tank with a valve attached at the top, at this time there is still oxygen inside, but at the beginning of the fermentation process CO2 will be released to the outside, but CO2 is heavier than oxygen. So that, at this point oxygen will be pushed to the upper part and released through the valve, by the time there is only CO2 left in the tank, it becomes anaerobic. This process is called semi-carbon dioxide. 

Compared with aerobic fermentation which is the faster fermentation and needs to be controlled to avoid over-fermentation, then the anaerobic fermentation can extend fermenting time to induce the development of new complex and exciting flavors.

Kenneth Davis, a coffee expert, has commented that the anaerobic environment favors lactic acid fermentation, creating novel aroma characteristics. Gabriel, the director of quality and market development at Daterra Coffee in Brazil, described the first time tasting anaerobic-fermented coffee: “It was a super crazy taste of tropical fruits such as mango, papaya; super floral, with some alcohol in the aftertaste – but all well balanced and pleasant.”

Although anaerobic fermentation is still in its early stages, it can be interesting for the coffee industry, creating flavors that are richer, more complex, and high-quality could offer higher price opportunities. 

Carbonic maceration processing method

The carbonic maceration method was first introduced by barista Saša Šestić in 2015 and won the Barista Championship, evolving from the wine fermentation method. Carbon dioxide processing in wine (vine) is pumped into fermented grapes without breaking the skin of the fruit, this fermenting process is not caused by fungi but occurs from intracellular cells, or from the inside out.

Ripe coffee berries. Photo: mtpak

For coffee, people put the harvested coffee cherries in an airtight container and then pump CO2  into it to create a CO2-rich environment, this gas is enough to allow the destruction of the cells of the pulp of coffee berries from inside out.

The aroma and flavor compounds generated by the absorption of CO2 are received by the parchment (husk) that contribute to the quality of the brewed coffee cup, characterizing this processing as the movement of tannin and anthocyanin into the bean where many chemical reactions take place,  After a long period of carbon processing that can take months to produce the desired coffee flavor, coffee berries continue to be processed by drying or washing.  The absorbed prominent flavor characteristics are strawberry, cherry, raspberry, or banana flavor. 

Oro mushroom fermentation processing method

This process begins when the selection of fully ripe fruits is harvested, the selected fruit is rubbed to the mucous part and placed in airtight Grainpro bags, then added Oro yeast (Saccharomyces cerevisiae) from the French company Lalcafe, the fermented bags must be airtight to perform anaerobic Oro fermentation (without oxygen). Oro yeast can work well even where the temperature is low (minimum 15°C  inside the tank) so it can be used at almost different heights, in addition, the yeast can control the fermentation process, against microorganisms that can cause undesirable defects. The longer fermentation time allows the coffee beans have enough time to absorb the metabolites as fermentation produces special flavors such as strawberry, tropical fruit, and black tea, floral aroma, brightness, high acidity, and complexity. After fermentation, the coffee is washed and left to dry on the bed for about two to three weeks.

Giving basah processing method (Wet Hull)

Giving basah method (wet rind) is used as an Indonesian traditional processing method to create a flavor that characterizes regional coffee. Coffee processed according to Giling basah acquires a full mouth feeling, and lower acidity, but aroma and sweetness are detected lower than in other methods.

After harvesting, the coffee berries are put through a rubbing machine to remove the outer skin, the rest of the fruit including the pulp will be fermented overnight then the pulp and mucus after this fermenting will be washed, the mucus after that is just only the parchment (husk). Wet-shell coffee is only dried for a few hours as the humidity is about 50% and the beans are still puffy.

The farmers were able to sell partially processed coffee to buyers. At this stage, coffee is dried to 25 or 35% and then sent to the husk rubbing machine, after being peeled, it will continue to be dried about 9-11%. Being preserved, packed, and shipped to roasters.

Barrel Aged coffee processing method

This process is to brew coffee in barrels, used wine barrels acquired from distilleries, especially oak barrels. Because old oak barrels have been used to brew whiskey and rum for many years, most of the natural flavors have seeped into the wood inside, using this wooden barrel to brew coffee, the beans will absorb these flavors.

Coffee beans are put in wooden barrels for about two to three weeks, however, it can leave them longer to create a more pronounced flavor.

Put coffee beans in wooden barrels. Photo: beanground

Each batch of coffee crafted in a wooden barrel produces different flavors because each wooden barrel has a specific flavor depending on the age and amount of flavor absorbed that the barrel still retains, in addition, the type of barreled wood also adds a little aroma to the coffee beans. After being used for a while, the flavors held in the wood will gradually decrease, resulting in the coffee beans also absorbing less of that characteristic flavor. Barrels that were previously used to brew whiskey will give a more savory flavor, a bourbon barrel will give sweeter coffee and a strong vanilla flavor, and rum barrels will have a sweet, spicy flavor and a little caramel in the beans. 

Low acidity coffees like Indonesian coffee, and Sumatra coffee beans have been semi-dry processed, and are suitable for brewing in wooden barrels, it can produce complex and rich flavors. Although it is brewed in a wine barrel, the coffee only has an alcoholic flavor without the alcohol content.

Adding fruits to the fermentation process method

In 2017, a Brazilian coffee producer, Bruno Souza started using citrus fruits such as tangerines in the process of fermenting coffee for 72 hours, then processing as usual. And this coffee scored 87 points in the Cup of Excellence 2018. But at the time, Bruno himself can’t be sure if this resulted from the mandibles he put in or if it was all from coffee beans. 

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Adding fruits to the fermentation. Photo: perfectdailygrind
Drying coffee beans on a rig after fermentation. Photo: perfectdailygrind

In order to estimate that the fermentation process is just a relative part, Lucas Louzada, a professor at the Federal Institute Venda do Imigrante in Brazil, concluded that “We know nothing about coffee fermentation from a scientific perspective”. Adding fruit to the fermentation process can be said to have an impact, but how that affects it needs further study.

Producers must note that there is still not much concrete understanding of this processing method, it will cost more to produce, but it is not certain that the desired results will be obtained and that some users will like it, the rest will hate it.


Microbial Wastewater Treatment, 2019. Anaerobic process: Anaerobic processes comprises of complex reaction network of biological and chemical reactions.

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