- Co-fermented and yeast-inoculated coffees share some similarities that produce flavours beyond the coffee cherry itself.
- Co-ferments are coffees in which external organic substrates (such as fresh fruit pulp, musts, or cacao pulp) are added during fermentation. Yeast inoculation is the process of intentionally adding specific strains of yeast during fermentation.
- Both allow producers to control flavour and sensory profiles, create consistent coffees, and potentially increase value.
- Yet the latter is often considered superior to the former, prompting the question of how different they really are. The main differentiating factor could be the introduction of new sugars and ingredients with defined flavours.
Co-fermented coffees are still divisive, but they are becoming an increasingly bigger part of specialty coffee. Appearing at more trade shows and on café menus, it’s clear that some industry professionals and consumers are embracing these processing innovations.
As they diversify and become their own category, similar to how we classify different processing methods, the need to formally define co-fermented coffees emerges – especially as confusion persists with infusion processing methods.
There are certain similarities between co-ferments and yeast-inoculated coffees. Both involve using external organic substrates and compounds to produce flavours that terroir alone can’t create; yet, the former is sometimes perceived as more “artificial.”
To distinguish between the two and understand why negative perceptions persist, I spoke to Marty Pollack at Torch Coffee and Diego Robelo at Aquiares Estate.
You may also likeour article on why co-fermented coffees are becoming a category of their own.
Interest in new processing methods rises
The demand for “funky” tasting coffees is increasing, especially among younger generations and coffee markets in East Asia and the Middle East, where fermented flavours are popular and rarity or exclusivity are highly prized.
Producers then had an opportunity to capitalise on this demand. Experimental and advanced processing methods enable them to develop specific sensory profiles with more interesting and prominent flavour notes. Moreover, novel processing techniques can increase cup scores by a few points, meaning farmers can add more value to their coffee and potentially receive higher prices.
Experimental processing, however, requires refinement, the necessary equipment, and sufficient capital. Without these, farmers face significant financial risk, sacrificing large volumes of cherries for little to no reward.
Previously, coffee producers experimented with processing by altering different fermentation methods – extended fermentations, carbonic maceration, and introducing various yeasts. However, with infused and co-fermented coffees now on the market, the lines between different experimental processing methods have become increasingly blurred.
“An infused coffee has been fermented on its own and is then infused with another ingredient,” says Diego, the general manager of Aquiares Estate in Costa Rica. “Those ingredients don’t aid with fermentation; the coffee is just absorbing them.”
Although there are no formal definitions for both infused and co-fermented coffees, many agree on the following descriptions:
- Infused coffee: Flavouring agents or additives are introduced externally, typically during or after fermentation, or post-harvest processing. These additions can include concentrated fruit powders or extracts, spices, essential oils, or synthetic flavourings such as artificial vanilla, hazelnut oil, or caramel essence.
- For example, coffee is sprayed with synthetic vanillin to create a “vanilla” flavour, or green coffee is treated with hazelnut oil during storage to impart a nutty taste.
- Co-fermented coffee: External organic substrates (such as fresh fruit pulp, musts, or cacao pulp) are added during fermentation, producing flavour influences beyond the coffee cherry itself.
- For example, coffee is fermented with frozen passion fruit pulp or cacao pulp alongside the mucilage.
The controversy surrounding infused and co-fermented coffees
Producers have long been utilising fermentation in coffee processing, including anaerobic and lactic fermentation, for instance, to alter flavour profiles. Yet, the emergence of co-fermented, and most notably, infused coffees in the late 2010s sparked considerable debate about flavour manipulation and transparency.
Since its inception, specialty coffee has prioritised terroir, origin, and careful cultivation and processing, all of which highlight naturally occurring flavour notes. In keeping with this point of differentiation, some view infused and co-fermented coffees, which they argue create synthetic flavours, as being at odds with industry values.
Infused coffees are a particular point of contention. The growing use of artificial ingredients and essential oils for infusion processing methods raises questions about flavour authenticity and even health concerns, especially when there is little to no transparency about the use of additional ingredients.
The debate also extends to competitions and auctions. The 2024 Best of Panama competition notably excluded coffees which “were found to be altered from their natural DNA expression… by using foreign additives”. Organisers cited a desire to “protect the authentic identity” of the country’s coffee sector, which consistently commands premium prices on the international market.
The decision sparked mixed reactions within the industry. While some commended the prioritisation of “purity” and terroir expression, others stand firm in the belief that infused and co-fermented coffees are a welcome innovation in processing and flavour, especially when producers benefit.
Is co-fermentation similar to yeast inoculation?
Defining and differentiating between experimental processing techniques has become a new challenge in specialty coffee. There are now varying grades, qualities, and categories for these new processing methods, leaving the market to contend with the struggle of ensuring transparency to consumers.
With many agreeing that co-fermentation strictly involves the use of organic substrates (most notably fresh fruit pulp) to imbue new flavours or enhance existing ones, it raises the question of how different it is from yeast inoculation – a more commonly accepted practice in specialty coffee.
Borrowed from beer and winemaking, yeast inoculation involves introducing specific yeast strains to the coffee before or during fermentation. A yeast strain is a specific variant of a yeast species that possesses a unique set of genetic traits, influencing how it ferments sugar and affecting the final product’s flavour, aroma, and fermentation speed. One of the most prominent examples in the coffee, beer, and wine industries is Saccharomyces cerevisiae, which can be controlled in a number of ways to create a huge range of different flavour profiles.
Much like co-ferments, the process involves using organic substrates, compounds, and microorganisms to produce specific sensory profiles that cater to the preferences of niche markets. Coffee producers can utilise local yeast strains or buy commercially available strains to impact flavour profiles.
However, to a certain extent, “accidental” yeast inoculation during coffee processing is unavoidable.
“Fermentation is the breakdown of sugar by microorganisms. This will occur with or without the external introduction of yeast,” says Marty, the co-founder of Torch Coffee in China. “There are plenty of naturally occurring yeasts and bacteria all over and in the coffee cherry that will participate in fermentation.”
The use of specific yeasts, rather than relying solely on strains that are naturally present, as well as the timing of when the yeast is introduced, are the differentiating factors. Processing and fermentation expert Lucia Solis refers to this as “wild fermentations” (relying on yeast and bacteria found in the environment) versus “inoculated fermentations” (purchased or cultivated yeast and bacteria).
Co-fermentation and yeast inoculation share similarities, but the key difference lies in the inclusion of new sugars, specifically, Diego explains.
“With yeast-cultured coffees, you introduce yeast strains and new microorganisms that will digest and ferment the sugars in the fruit and mucilage of the coffee,” he adds. “But with co-ferments, you are not only introducing a new microorganism, but also a new sugar source.
“A co-ferment can be with fruit, such as guava or watermelon, that also has sugars that ferment at the same time as the coffee does,” he adds. “Those fruits also contain other microorganisms that will alter the fermentation, too.”
In theory, co-fermentation could add more complexity to the fermentation process and potentially provide producers with more opportunities to increase sweetness and customise flavour notes.
Similarly, most fruits already have their own distinct flavours and aromas, meaning co-fermentation increases the chances of influencing the coffee’s final flavour profile. For some, this may be perceived as more “artificial” than simply using different yeast strains, which only break down sugars, rather than introducing new ones, and indirectly influence flavour.
However, the impact of using fruit to co-ferment coffee may be more minor than we think. The Hachi Coffee Project, a pioneer in experimental processing, recently shared data suggesting that only 3% of the fruit used in co-fermentation ends up in the cup, signalling that the specific flavours of fruit may have little influence on coffee.
Seeking clarity is challenging, but appreciation is growing
Co-fermentation and yeast inoculation are not straightforward processing techniques. But as coffee processing diversifies, splitting into newly defined categories, the need for clarification intensifies.
“One of the big problems we have right now is a lack of formal definitions for different terms,” Marty says. Despite increasingly noticeable differences, the terms “infused,” “flavoured,” and “co-fermented” are often used interchangeably, exacerbating confusion and concerns about transparency.
Ultimately, the real and most significant danger lies in inadvertently stripping producers of the value of their coffee and retaining it in majority-consuming markets.
“The main point is not fighting about the terms but rather asking everyone to be transparent about what was done to a coffee during and after the fermentation and drying stages,” Marty adds. “If anything was added to this process, tell people what and how it was added. These things shouldn’t be seen as trade secrets but rather as a part of real transparency.”
This is the collective responsibility of all supply chain actors, not just producers who process coffee. Whether it’s infused coffees, co-ferments, or yeast inoculations, all industry professionals must communicate honestly and transparently about the use of additional compounds and microorganisms, especially as coffee’s health claims are under greater scrutiny.
“For all the coffee we sell at Torch, we tell people what happens during the entire process, including how many days of fermentation under what conditions – anaerobic, underwater, or soaking in mango juice, for example,” says Marty. “If anything is added, we explain clearly and honestly so we don’t have any trouble marketing them.”
As these techniques evolve, there’s also a growing appreciation for co-fermentation and yeast inoculation. Although not all coffee professionals and consumers will embrace them, more people are increasingly recognising the skill and expertise needed to carry out these processing techniques successfully.
“What I like about co-ferments and yeast culture in their ‘pure’ forms is that there is a science behind them,” Diego says. “You need to understand more of the behaviours of the ingredients that you add in.”
Producers like Diego Bermudez, Allan Hartmann, and Matheus Antonaci of the Hachi Project are leading these efforts. Their work employs biotechnology, including the utilisation of various yeast strains during fermentation, to pinpoint and highlight existing flavours in coffee. In time, there’s potential to reimagine what’s possible in terms of coffee’s sensory characteristics.
The debate about infused, co-fermented, and yeast-inoculated coffees requires nuance and an open mind. Ultimately, it underscores the importance of honesty and transparency in coffee processing.
Simultaneously, if we seek to define these coffees more clearly, it’s imperative that those who have direct experience creating and refining these techniques – producers and farm workers – lead these conversations.
Enjoyed this? Then readour article on why we should treat infused and co-fermented coffees differently.
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