Fermentation in coffee: the basics

published on May 15, 2024 — by Marc-Alexandre Emond-Boisjoly — 15 mins of reading —

Fermentation: Transformation of organic matter by enzymes secreted by micro-organisms. (ref Larousse.fr)

As we saw earlier, the coffee treatment process "only" serves to pulp the coffee cherry to obtain a bean with a moisture content suitable for storage and delivery. Whatever the process used to treat the coffee cherry, there is always a fermentation stage.

Whether in a wet process, where the cherry is first cleaned of its pulp (in whole or in part), or in a dry process, where the cherry is dried directly, fermentation takes place to detach the mucilage (pulp) from the bean, reduce its moisture content and release the aromatic components of the coffee [1, 2, 3, 4, 5]. The type of fermentation chosen will depend mainly on the terroir, the coffee variety, the climate and the desired aromatic profile.

What interests us today is controlled fermentation. We'll be looking at 3 basic types of fermentation: carbonic maceration, aerobic fermentation and anaerobic fermentation. In our next article, we'll look at the variations and experiments carried out by farms to enhance or even modify coffee aromas.

Controlled fermentation makes the process more stable, increases the consistency of the finished product, enhances the final quality of the coffee by highlighting the terroir and variety, and ultimately results in a higher price for the green coffee.

Cerises de café en cuve de macération carbonique

Carbonic maceration

Fermentation in a medium saturated with carbon dioxide

Carbonic maceration comes from the wine industry. In coffee, it involves fermenting whole cherries in a hermetically sealed vat saturated with carbon dioxide. The carbon dioxide may be added artificially or, in the case of semi-carbonic maceration, come from the natural decomposition of the cherries. The pressure created by the gas will crush the cherries, producing juice. This juice can then be recovered for later use.

This step is generally a preparatory stage for a conventional process (dry or wet). It slows down the cherry rotting process and seems to optimize the sensory properties of natural coffees [7].

Carbonic maceration produces characteristic fruitier flavors such as strawberry, raspberry, cherry or banana [8].

Aerobic fermentation

Fermentation in the presence of oxygen

Aerobic fermentation is the traditional and least expensive fermentation method. It can be carried out in 3 ways [6]:

  • dry: coffee beans (with mucilage) are accumulated in open bins but are not mixed. In this case, fermentation time is highly dependent on ambient temperature. Fermentation is relatively short and not very controllable, but when properly carried out, it produces complex, fruity, chocolatey coffees.

  • immersed: always in open bins, the grains are immersed in water and mixed at the start of fermentation. The water dilutes the sugars and regulates the temperature, extending the fermentation time. The more uniform fermentation results in sweeter coffees with hints of caramel.

  • in closed tank with oxygen supply and continuous mixing: this continuous fermentation produces coffees with notes of hazelnut, vanilla and flowers, but earthier notes can also appear.
Cuves de fermentation anaérobique pour le café

Anaerobic fermentation

Fermentation in the absence of oxygen

Anaerobic fermentation involves placing the coffee (the cherries or, more commonly, the beans and their mucilage) in a completely sealed environment, with or without liquid.

This is the fermentation that has been most developed in recent years. You can see coffees that have undergone fermentation for over 120 hours!

This type of fermentation, in an oxygen-free environment, limits the formation of certain fungi and increases the effectiveness of bacteria and yeasts naturally present on coffee cherries or beans, or which have been introduced [7]. This step also reduces the drying time of the beans [9].

Anaerobic fermentation produces more consistent results, as it is easier to control in terms of temperature and time. Correctly executed, this fermentation produces a sweet, fruity cup, but the slightest misalignment in parameters can create moldy, fermentative or even fungal aromas [4].

According to studies, longer anaerobic fermentation contributes to the development of caramel-like acidity and sweetness.


Fermentation is a crucial stage in the smooth transition from coffee cherry to green bean. In addition to cleaning the bean pulp, it helps to limit the development of fungi, shorten the final drying time and obtain a homogeneous result.

We've been particularly interested in fermentation for only a few years now, for its ability to develop powerful flavors. The use of controlled fermentation, mainly anaerobic, can blur the flavor map: it can sometimes be difficult to determine varieties and origins depending on the method used.

In our next and final article in this series, we'll take a quick look at current experiments and see why fermentation is a hot topic right now.

Many thanks to Forest Coffee, Carolina Ramirez (Unblended), David Batrès, Coffee Quest and Sebastian Ramirez for the photos.


[1]  https://www.luxia.coffee/

[2] “Coffee fermentation: Expedition from traditional to controlled process and perspectives for industrialization”, H. Elhalis, J. Cox, J. Zhao, Applied Food Research, Volume 3, Issue 1, June 2023, https://www.sciencedirect.com/science/article/pii/S2772502222002086

[3] “A Consumer Assessment of Fermented Green Coffee Beans with Common Beer/Wine Yeast Strains for Novel Flavor Properties”, N. Calderon, G. Zhujun Jiang, P. A. Gibney, R. Dando, Fermentation, 2023, 9(10), 865., https://www.mdpi.com/2311-5637/9/10/865

[4] “A Review of Coffee Processing Methods and Their Influence on Aroma”, B. Girma, A. Sualeh, International Journal of Food Engineering and Technology 2022; 6(1): 7-16, https://www.researchgate.net/profile/Abrar-Sualeh/publication/359746797_Bealu_Girma_Abrar_Sualeh_A_Review_of_Coffee_Processing_Methods_and_Their_Influence_on_Aroma/links/624ca2bdd726197cfd3e1403/Bealu-Girma-Abrar-Sualeh-A-Review-of-Coffee-Processing-Methods-and-Their-Influence-on-Aroma.pdf

[5] “Challenges in Specialty Coffee Processing and Quality Assurance“, P. Poltronieri, F. Rossi, Challenges 2016, 7(2), 19, https://www.mdpi.com/2078-1547/7/2/19

[6] https://www.fantine.io/2022/coffee-fermentation-things-you-didnt-know/

[7] “Coffee bean processing: Emerging methods and their effects on chemical, biological and sensory properties”, N. A. Febrianto, F. Zhu, Food Chemistry, Volume 412, 30 June 2023, https://www.sciencedirect.com/science/article/pii/S030881462300105X

[8] “Aroma profiles and cupping characteristics of coffee beans processed by semi-carbonic maceration process”, W. Jitjaroen, R. Kongngoen, L. Panjai, Coffee Science, e182119, 2023, https://coffeescience.ufla.br/index.php/Coffeescience/article/view/2119

[9] “Influence of fermentation conditions on the sensorial quality of coffee inoculated with yeast”, M. C. Batista da Mota, N. N. Batista, M. H. Sances Rabelo, D. E. Ribeiro, F. Meira Borém, R. Freitas Schwan, Food Search International, Vol 136, Octobre 2020, https://www.sciencedirect.com/science/article/pii/S096399692030507X

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