By Simon Gautherin & Zest Coffee Team

Coffee fermentation is usually talked about in terms of flavour: more fruit, more intensity, something you have never tasted before. James Hoffmann and Lucia Solis' Fermentation Project made a different case. Fermentation is just as much about control, consistency and repeatability for the producer.

For us at Zest, that was less a new idea than a reminder. Our coffee team has been running fermentation projects at origin for years, with the Bosques Verdes co-operative in Peru, Pillcocaja in Ecuador and Jack Murat here in Australia, alongside experiments such as koji fermentation on forest coffee. Those projects were designed to make fermentation controlled and repeatable for the producer. Flavour was part of the brief, but never the whole of it.

What we have not always done is tell that part of the story. When we have talked about these projects publicly, we have mostly talked about what ended up in the cup. I am as guilty of that as anyone. I first came across Zest through the Jack Murat project, and like most coffee drinkers, I thought about it mainly in terms of flavour.

So this article does two things. It explains what The Fermentation Project was and what we learnt from tasting it, and it looks back at our own fermentation work through the lens the project gave us.

What is James Hoffmann's Fermentation Project?

The Fermentation Project is a global coffee tasting created by James Hoffmann and fermentation specialist Lucia Solis. It takes one coffee, processes it four different ways, and lets people around the world taste the results side by side.

The coffee came from Finca San Miguel Urias in Antigua, Guatemala. It was divided into four processing treatments:

• Mechanically demucilaged (the control). The mucilage surrounding the coffee seed was removed by machine, with no intentional fermentation stage.
• Wild fermentation. Around 48 hours of fermentation using the naturally occurring microbial population.
• Lactobacillus inoculation. Around 48 hours of fermentation with a selected Lactobacillus culture.
• Selected yeast fermentation. Around 48 hours of fermentation with a selected Saccharomyces yeast.

The underlying coffee stayed broadly the same, while the approach to fermentation changed.

That matters because when we discuss fermentation in coffee, we are normally comparing completely different coffees. We might taste an anaerobic natural from Colombia beside a washed coffee from Ethiopia and conclude that processing explains the difference. But we have also changed the country, the variety, the altitude, the producer, the harvest conditions and the drying.

It becomes almost impossible to isolate what fermentation actually contributed. With this project, the comparison was much cleaner. It was not a perfect laboratory experiment, and coffee processing rarely can be, but the same source material treated four ways gave us a far more useful reference point.

Why Is Coffee Fermented In The First Place?

Coffee is fermented to break down the sticky mucilage left on the seed after pulping, so it can be washed off before drying. Long before fermentation was used to market exotic coffees, it had this very practical job in washed coffee processing.

It is quite an ordinary processing problem when you think about it. You have harvested coffee, you need to remove the fruit, and fermentation is one of the ways to make that happen.

Of course, microorganisms do much more than make mucilage easier to wash away. They consume compounds, produce metabolites and change the chemical environment around the seed. Some of those changes influence the flavour we experience later, which is exactly why fermentation is so interesting from a sensory perspective.

But Lucia's approach puts the practical purpose back at the centre. If fermentation has to happen anyway, then controlling it is valuable for more than the flavours it might create. It makes the process more predictable. For a producer, that distinction is significant.

Why The Mechanically Demucilaged Control Mattered

The mechanically demucilaged coffee was the least glamorous part of the project, but educationally it may have been the most important.

By removing the mucilage mechanically, the project gave us something close to a baseline. We could taste the three fermented versions against it and ask not only whether they differed from each other, but what had changed relative to the original coffee.

That sounds obvious, but we rarely get to do it. In most coffee tastings there is no control. If we taste a heavily fermented coffee, we usually do not have an identical lot from the same harvest, processed at the same time without that fermentation. We end up making assumptions about which flavours came from the variety, which came from the farm and which came from processing.

Here, more of those variables were held steady, so the differences between the cups told us much more.

Wild Fermentation VS Inoculated Fermentation In Coffee

Wild fermentation relies on the microorganisms naturally present on the coffee and in the processing environment. Inoculated fermentation adds selected cultures, such as a specific yeast or Lactobacillus, to steer which microbes do the work.

Wild fermentation is much closer to how coffee has traditionally been fermented on farms, where the producer creates the conditions and lets the existing microbial community develop. There can be a lot of beauty in that process, but there can also be variability. Different microorganisms may become dominant depending on temperature, fruit condition, water, hygiene, equipment and many other factors.

The Lactobacillus and yeast treatments approached the same problem differently. By introducing selected microorganisms, Lucia could exert more influence over which populations were active during fermentation.

This is where there is sometimes unnecessary confusion in specialty coffee. Inoculation can sound artificial because something is deliberately added, but it is completely normal in other fermented products. Wine, beer, bread, cheese and yoghurt all use selected microbial cultures depending on the desired process and outcome.

The goal is not to add a flavour directly to the coffee. It is to influence the biological process taking place around it.

Controlled Fermentation Does Not Mean A Louder Coffee

Control can simply mean achieving a similar result again tomorrow. It is easy to assume that more precise fermentation exists to produce more specific or unusual flavours. That is true, but it is only part of the picture.

If you are a producer, repeatability is incredibly valuable. You have spent months growing a crop, you have a short harvest window, and once the cherries are picked you are working with something perishable. If a fermentation goes badly, the consequences are far more serious than an experiment going wrong in a cafe or a roastery.

There is a huge practical benefit in understanding which microorganisms are present, how they behave and how to create conditions that favour the outcome you want. The result may not be a coffee that tastes radically more fermented. It might simply be cleaner, more consistent or easier to reproduce.

In other words, fermentation is a tool to control a process, and flavour is one of several possible outcomes.

Zest's Fermentation Projects At Origin: Peru & Australia

Tasting The Fermentation Project sent us back to our own work, because this is the thinking our coffee team started from. We've highlighted two below, but we've also run fermentation projects at Pillcocaja in Ecuador, and El Vergel in Colombia (twice).

Bosque Verdes, Peru - 2019

When our coffee team began working with the Bosques Verdes co-operative in Peru, the question was not only what flavour we could create. It was how to make fermentation controlled, consistent and replicable for the producer.

That is why the project involved fermentation tanks, pH meters, wireless temperature probes and two selected coffee yeasts, LalCafé Cima and LalCafé Intenso. With those tools, the same cherry could be fermented in the most controlled way possible, and in a way that could be repeated the following year.

The yeasts improved cup quality. They also extended the shelf life of the coffee, which is a big deal for a producer's sustainability.

Jack Murat, Australia - 2021

After Peru, the team took the same two yeasts to Jack Murat in Australia. The work started with a farm visit by our Head of Coffee, Aryan Aqajani, and our colleague Darren. They tasted the farm's mechanically washed coffee, studied the workflow and learnt the limitations. From there, they looked for processing techniques that would improve quality while staying easy and replicable.

The result was very predictable, in the best sense. The yeasts did for the Australian coffee what they had done for the Peruvian one: a consistent flavour profile and a longer shelf life.

A mechanically washed baseline, a selected yeast and a result you can predict. Reading that back after The Fermentation Project, the parallels are hard to miss.

The Half Of The Fermentation Story We Did Not Tell

If control and repeatability were always part of our projects, why did this tasting feel like a fresh perspective? Because we marketed those projects almost entirely on flavour.

That is understandable. Flavour is what people taste, and it is the easiest part to get excited about. I still find that side of fermentation incredibly exciting. Our koji experiments are a good example, because koji is not part of conventional coffee processing and the interest was in seeing what happens when you introduce something unfamiliar.

But for the coffee team, the intentions always went beyond flavour creation. The Fermentation Project gave that side of the work a clear public language, and the four cups made it something you could taste.

It also sharpens the questions we ask of any fermentation project:

• Does the process create more fruit character, change acidity or increase perceived sweetness?

• Is it stable, and how repeatable is it?

• Can the producer implement it consistently with the equipment and time they have?

• Is the additional complexity justified?

It is relatively easy to produce one unusual coffee and be excited by the result. It is much harder to understand why it happened and then reproduce it intentionally. That second part is where much of the real value sits.

Is There A Best Coffee Fermentation Method?

No. Each method solves a different problem, and I would be cautious about turning this tasting into a ranking.

The takeaway is not that inoculated fermentation is better than wild fermentation, or that wild fermentation is somehow more authentic. Mechanical demucilaging is not inherently less interesting either.

A producer who understands their local microbial environment extremely well may achieve excellent, consistent results through wild fermentation. Another may benefit from inoculation because their conditions fluctuate more, or because they want a very specific fermentation pathway. Another may decide that fermentation adds unnecessary risk and prefer to remove the mucilage mechanically.

The right choice depends on the coffee, the environment, the infrastructure, the economics and the producer's objective. We spend a lot of time in coffee looking for the best technique, when the more useful question is whether a technique suits the situation in front of us.

How Did The Four Fermentation Project Coffees Taste?

The four coffees were not dramatically different, and for an educational tasting that was a strength.

If one coffee tasted completely conventional and another tasted like an overwhelming tropical fruit ferment, spotting the difference would be easy. You would notice it immediately, but you would not learn much beyond the fact that the coffees were different.

Here, you had to spend more time with them. Some differences were easier to notice as the cups cooled. The comparison became about shifts in acidity, fruit character, texture, sweetness and balance, not one dominant processing flavour.

That kind of tasting forces you to be specific about what you are perceiving. It also proves the point of the whole project: controlled fermentation can change a coffee without making it louder.

What Zest Is Taking Away From The Fermentation Project

The project did not change what we believe about fermentation. It reminded us what we have believed all along, and showed us we should say it more clearly.

Fermentation can be a tool to discover new flavours, and it can be a tool to make an existing process more consistent. It can increase sensory complexity, or simply help a producer remove mucilage reliably. It can be experimental and creative while also being practical and risk-conscious. Our projects in Peru, Ecuador and Australia have always tried to do both.

Three things we are taking forward:

• Tell the whole story. When we share a fermentation project, we will talk about what it does for the producer as well as what it does in the cup.
• Keep using controls. Tasting a fermented coffee beside its unfermented baseline is the clearest way to see what fermentation changed.

• Keep exploring flavour. Control and curiosity are not in competition. The more repeatable a process is, the more confidently we can experiment with it.

Thank you to James Hoffmann and Lucia Solis for giving the coffee community a shared set of cups to taste and a clearer way to talk about fermentation. Sometimes exploration means finding something new. Sometimes it means looking again at work you have already done and seeing it properly.

Coffee Fermentation FAQ

What is coffee fermentation?

Coffee fermentation is the stage of processing where microorganisms such as yeasts and bacteria break down the sugars and mucilage around the coffee seed. It makes the mucilage easier to remove and can also influence the flavour of the finished coffee.

What is inoculated fermentation in coffee?

Inoculated fermentation is when a producer adds a selected culture, usually a specific yeast or Lactobacillus, instead of relying only on the microbes naturally present. It gives the producer more control over the fermentation and makes results easier to repeat.

What is wild fermentation in coffee?

Wild fermentation uses the microorganisms naturally found on the coffee cherry and in the processing environment. It is the traditional approach, and its results can vary with temperature, hygiene, water and fruit condition.

What does mechanically demucilaged mean?

Mechanically demucilaged coffee has its mucilage removed by a machine instead of being broken down through fermentation. In The Fermentation Project it served as the control, the baseline the three fermented coffees were compared against.

Does fermented coffee always taste funky?

No. Controlled fermentation is often used to make a coffee cleaner and more consistent, not more intense. In The Fermentation Project, the differences between the four coffees were subtle.

Who is behind The Fermentation Project?

The Fermentation Project was created by James Hoffmann and Lucia Solis, using a coffee from Finca San Miguel Urias in Antigua, Guatemala, processed four different ways.