January 25, 2021

How do microorganisms affect fermentation & the sensory profile of coffee?


As the coffee industry develops and grows, producers and researchers continue to innovate and push boundaries in regards to processing and fermentation. The end goal is to deliver unbelievable flavours and improve cup quality.

Whenever fermentation is involved, producers and scientists experiment with various microorganisms, and examine how their unique relationship with the process can affect a coffee’s sensory profile and cup score.

To further examine how microorganisms affect fermentation and a coffee’s sensory profile, I spoke with a producer, a Q grader, a professor, and a roaster, all involved with the Nucoffee Artisans project in Brazil. I asked them about how tailoring and pairing unique microorganisms can affect coffee fermentation and improve cup profile. Read on to find out what they said.

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Fermentation, microorganisms, and controlled fermentation

Coffee fermentation is a naturally occurring process that starts to occur as soon as a coffee cherry is picked. It occurs as the water, sugar, and starches within the cherry begin to naturally break down into acids and alcohols

Fermentation typically occurs in one of two main ways: aerobic (an oxygen-rich environment) or anaerobic (an environment with no oxygen). Both fermentation styles can be controlled in different ways.

Whenever fermentation occurs, microorganisms are responsible for converting these sugars and starches into acids and alcohols. There are thousands of microorganisms that have been identified in fermentation, but some of the most common include yeasts (such as saccharomyces cerevisiae), bacteria (such as lactobacillus), and fungi. 

Each individual microorganism affects fermentation (and therefore coffee flavour) in an acutely different way. While we understand that some (in particular saccharomyces cerevisiae and lactobacillus) affect the smell, colour, and pH of a coffee, the effects that other microorganisms have on fermentation are still being studied.

Rosane Schwan is a professor at Universidade Federal de Lavras in Lavras, Minas Gerais. She tells me more about how microorganisms affect fermentation. 

“The main microbial groups of coffee include bacteria, yeast, and filamentous fungi,” Rosane says. “Particular microbial genera/species vary among coffee-producing areas, probably due to environmental conditions, coffee varieties, and processing methods. [They consequently affect] cup quality [differently].

“Processing methods will vary from farm to farm, depending on climate conditions, fruit maturation, capital availability, machinery, and technology.”

More recently, controlled fermentation has been adopted across the coffee sector to offer increased security for producers who experiment with coffee processing. By monitoring and controlling variables such as temperature and time, producers can more effectively manage the flavours of their coffee, and subsequently manipulate its sensory profile. 

Furthermore, it’s important to note that uncontrolled fermentation is still not fully understood, and could (in worst case scenarios) end up being potentially harmful to the end consumer.

Natural fermentation and starter cultures

In comparison to beverage sectors where fermentation has been used for thousands of years (such as beer and wine), fermentation in coffee is still in a relatively early stage of understanding.

However, we know for certain that fermentation can occur both naturally, without external input from the producer, or through the deliberate use of “starter cultures”.

Natural fermentation relies on the microorganisms that are already present in and around a coffee cherry to break down the sugars and starches within. Using starter cultures, however, is like adding a new “ingredient” that kickstarts and guides fermentation in a certain way.

Rosane explains that each starter culture is unique. As a result, they can lead to a variety of final outcomes in terms of the flavour profile of a coffee. “The production of specific [flavour] compounds is due to culture starters’ different fermentation pathways during the complex fermentation process.”

She says that while natural fermentation can often be unpredictable and have an unusual impact on cup profile, “the Nucoffee Artisans [project] has selected culture starters that enhance coffee quality”. 

“Our research at UFLA proposed technological alternatives for greater control over fermentation. This involves a standardised process that guarantees the production of novel coffee flavours and [fosters the development of] desirable sensory profiles.

“In general, microbial performance was improved by the use of anaerobic conditions in closed batches. It also helped by inhibiting [the presence of] undesirable fungi and bacteria.”

Microorganisms and fermentation

The Nucoffee Artisans project has been the product of a development partnership between Syngenta-Nucoffee, UFLA, and Rosane. It has studied controlled fermentation and its relationship with a variety of microorganisms.

By isolating selected microorganisms, the project set out to “transform” the chemistry of coffee fermentation and generate new flavour and aroma precursors.

Jorge Fernando Naimeg, from Cerrado Mineiro, Minas Gerais, was one of the producers involved in the project. He says: “[The project] uses isolated yeasts from the coffee itself that are purified and multiplied.”

Producers then use these microorganisms in controlled fermentation. They carefully monitor temperature, pH, and time to improve consistency.

Jorge adds that this project also studies how different microorganisms react with different coffee varieties. He describes the results as “interesting”.

“[Even across] different varieties, altitudes, and processes, we all had similar sensory profiles.” Effectively, by controlling fermentation with the chosen microorganisms, producers were able to make their sensory profiles more consistent. 

Results have been tested for four years across major Brazilian growing regions, and have delivered the same flavour profile year after year at each farm. The idea is that when a green coffee buyer or roaster partners with a producer using these processes, they can be guaranteed the same level of quality on a regular basis, without seasonal fluctuation.

He adds that this project also supported producers to “trust” the technologies and research behind fermentation through its demonstrated results.

Finally, he notes that a well-communicated, thorough fermentation protocol gave producers a list of instructions to follow throughout the fermentation process. This, he says, helped them to understand and feel more confident about their results.

Changes in flavour

With more than 20 years of research in different microorganisms and fermentation methods, Nucoffee Artisans experts studied more than 3,000 different microorganisms with a focus on how they influenced fermentation and coffee flavour. In 2020 alone, the project passed on 383 microorganism kits to 323 producers (each enough to produce approximately 20 bags).

Jorge says the project allowed producers to isolate microorganisms which were beneficial for coffee fermentation. “This new innovative technology was able to reach the producer at an affordable cost,” he tells me. “It was relatively simple, and opened a new range of possibilities for us producers.”

This new range of possibilities is perhaps best explored in the unusual flavour profiles that these new fermentation techniques produce.

Brazil is the largest producer of coffee in the world. The vast majority of coffee grown in the country is natural or pulped natural processed. Often, Brazilian beans have a full body, low acidity, and sweet, chocolatey notes. 

However, by using these techniques, Brazilian producers can alter the flavour profile of their coffees. This helps them set themselves apart from others on the market.

As part of the Artisans project, producers have been trained to use the techniques, and have subsequently produced more than 1,000 lots scoring between 80 and 90 points.

Silvio Leite is a Q grader at Agricoffee. He says: “The flavours from [this project] can be simplified into three distinct groups… firstly predominantly sweet flavours (notes of brown sugar, lemongrass).

“After that, we have fruity coffees, tasting either of dried fruits (raisin, dates), or the ‘cooler side’ (such as mango, cherries, strawberries).”

Silvio also notes that the third group was characterised by an aftertaste of sourness that he described as “not pleasurable”, but noted that this was evidence where the “processes must be adjusted”.

Michal Socha is the head roaster at Single Origin in Poland. He tells me that the coffees he has sourced from this project are “very original and unusual” and described “very noticeable strawberry notes”.

“The development of such a culture of bacteria and yeast also inhibits the multiplication of pathogenic fungi,” Michal adds. “This positively affects the sensory quality of the coffee.”

Both concluded that altogether, thanks to the use of these unique microorganisms in controlled fermentation settings, the diverse range of flavours that were produced were unusual (and in some cases unknown) for Brazilian coffee. 

Using controlled fermentation to improve producer incomes

Using this project as a benchmark, we can conclude that experimenting with microorganisms in controlled fermentation has the opportunity to improve cup quality and consistency for the producer.

One of the main opportunities for producers is the effect that controlled fermentation has in terms of adding value. Normally, value is predominantly added in consuming countries by roasters. By leveraging fermentation processes to improve flavour and increase quality, producers can diversify what they’re able to offer and be more competitive in the marketplace.

Silvio says: “[By using] these possibilities and processes, producers may have what could be called a ‘new menu’ of coffee flavours on offer.

“This could serve a [much broader] range of buyers, such as those who like a very sweet or super fruity profile, [or even floral flavours].”

Additionally, Jorge says that by using microorganisms to improve consistency, as with the Nucoffee Artisans project, producers can offer buyers a more stable flavour profile.

“The controlled fermentation allows for the repetition of sensory profiles, and [can] boost the aroma, flavour, and acidity of coffees. 

“This allows different varieties to reach a similar flavour profile, yet with different nuances and intensities.”

Roaster & consumer interest

Across the global specialty coffee sector, there is an ever-increasing demand for fermentation. This is because it provides roasters and consumers with the opportunity to experience new and unique flavour profiles.

“I see it as a new market,” Jorge tells me. “[Especially] for consumers that seek new experiences and surprising cup profiles. This then [benefits the producers financially].

“As the process is handcrafted, very technical, and demands a lot of care, the consumers, I believe, will be willing to pay more for the coffee.”

This has been reflected in the results from the project. During International Coffee Week, the producers were recognised with a ranking of the top 50 lots. Today, there are more than 2,000 bags in stock scoring between 86 and 90 points.

Michal adds that these experimental coffees give roasteries unique opportunities to work with high-quality coffees with exotic flavor profiles. He also explains that these coffees in particular are also suitable for both filter and espresso. 

“Both we, as a roaster, and our customers, brewed this coffee using various methods, filter and espresso. With both methods, the coffee is fantastic.”

To seek out new markets for these coffees, Nucoffee have started conducting virtual cuppings in the US and Europe with the hope of generating further interest. For producers, the project has set out the aim of “stimulating the production of new coffee profiles” in the weeks and months to come. 

The Nucoffee platform works with more than 2,000 coffee growers, and the company believes that it is possible to introduce new technologies across a range of Brazilian farms to unlock new market opportunities and new flavours.

While controlled fermentation and microorganisms are still the subject of continuous research in the coffee sector, this project shows that there is considerable opportunity for producers, roasters, and consumers. The potential for producers to leverage these production methods to unlock new sensory profiles is massive. 

Enjoyed this? Then read Coffee Fermentation: What Is It & How Can It Improve Coffee Quality?

Photo credits: Nucoffee, AP Central Farm, Pantano Farm, Armadilllo Sitio, 

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