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Certain words in speciality coffee seem to appear everywhere these days: natural, washed, anaerobic, yeast fermentation, Lactobacillus, wild fermentation, inoculated fermentation, etc.
If you spend enough time around speciality coffee, you get familiar with the terminology, but that doesn't necessarily mean you understand what it actually means in the cup.
We've read about it, talked about it and tasted coffees described as "fermented". But we've never had the opportunity to taste the same coffee processed in several different ways specifically to understand what fermentation is actually doing to it.
What is The Fermentation Project?
On 3rd October 2026, we'll be taking part in The Fermentation Project, a global live tasting organised around four coffees that all began with the same starting material but were processed using four different approaches. The tasting will be livestreamed on James Hoffmann's YouTube channel, and we have to admit, we're genuinely curious about what we'll find in the cup.
The exciting thing is that we don't really know what to expect. And we think that's a good thing.
The idea behind the project is beautifully simple. Rather than comparing completely different coffees, origins or varieties, the project takes the same starting coffee and processes it in four different ways.
The coffee comes from Finca San Miguel Urias, owned by Hector and Lilian Leal and operated under Rueda Farms in the Antigua Valley of Guatemala. The variety is approximately 85% Caturra and 15% H1, with some Bourbon.
Lucia Solis processed all four lots, working closely with the farm team to ensure that the coffee was pulped, fermented, washed and dried according to the specifications for each process.
This gives us something we don't often get in coffee: a kind of controlled comparison.
Why does coffee need fermentation?
Before getting into the four coffees, it is worth taking a step back.
Fermentation isn't necessarily something unusual or experimental in coffee. In many washed coffee processes, it is simply part of the practical work of preparing the coffee for drying.
Once coffee cherries are harvested and pulped, the coffee seed is still covered in a sticky layer of mucilage. Fermentation can help break down this mucilage, making it easier to remove during washing.
But microorganisms don't simply remove the mucilage and disappear. During fermentation, microorganisms consume available nutrients and produce different compounds. Those compounds can influence the coffee's chemistry and potentially contribute to what we eventually experience as aroma, acidity, flavour and mouthfeel.
The first coffee: Mechanically Demucilaged
The first coffee is the one we're perhaps most interested in because it will give us our reference point. This coffee was mechanically demucilaged, meaning the mucilage was removed mechanically after pulping rather than being intentionally broken down through fermentation.
There is no fermentation stage here. That makes this coffee the control for the experiment.
The second coffee: Wild Fermentation
The second coffee was fermented for 48 hours using the naturally occurring microbial population.
Rather than introducing a particular microorganism, the fermentation is driven by the microorganisms already present in the coffee and its environment. This could include different yeasts and bacteria, and the microbial population can vary depending on the conditions.
The third coffee: Lactobacillus-Inoculated Fermentation
Then we get into the terminology that can make coffee fermentation sound like a microbiology lecture. The third coffee was fermented for 48 hours using an introduced Lactobacillus culture.
Instead of relying entirely on the microorganisms naturally present, a selected culture is introduced into the fermentation. Lactobacillus is a genus of bacteria associated with the production of lactic acid and other compounds, and this type of fermentation can influence the acidity and sensory character of the coffee.
The fourth coffee: Saccharomyces Yeast-Inoculated Fermentation
This coffee was fermented for 48 hours using a selected Saccharomyces yeast strain.
Saccharomyces is a genus of yeast that many people will recognise from beer and wine fermentation, and controlled yeast fermentation has also become an increasingly interesting area of experimentation in coffee.
What will we actually taste?
Will the four coffees taste dramatically different? Will the differences be subtle?
Right now, we have no idea.
We've done our research and tried to understand the basic principles behind each process, but reading about fermentation is very different from tasting the results side by side. That's why this project appealed to us. We're not approaching it as fermentation experts. We're approaching it as coffee nerds who want to understand something that is becoming increasingly important in speciality coffee.
We suspect we're not the only coffee enthusiasts who find fermentation confusing.
Plenty of coffees on the market are described using terms like "yeast inoculated", "lactic fermentation", "anaerobic fermentation", or "wild fermentation". Sometimes the descriptions sound incredibly technical, while the actual effect on the cup can be difficult to understand.
So rather than pretending we already have all the answers, we're using this tasting as an opportunity to learn.
Lucia Solis and the science behind the project
A major part of this project is the work of Lucia Solis, the fermentation consultant who worked with the farm team on these coffees.
Lucia studied Viticulture and Enology at the University of California, Davis, specialising in microbiology and fermentation science. She subsequently spent nine years working in wine production in Napa Valley before moving her focus to coffee.
Her work is particularly interesting because it isn't simply about creating unusual flavours. For her, fermentation has to be practical.
Lucia has also produced videos explaining some of these processes, we watched them as part of our preparation for the tasting. If you're interested in joining the experiment, they're well worth exploring before 3rd October.
The coffee behind the experiment
An experiment like this doesn't happen without the people who get the coffee from the farm to our cupping table.
The green coffee for the project comes through Caravela Coffee, the green-coffee partner behind this lot. Caravela has worked in Guatemala since 2016, buying, milling and exporting speciality coffee while working closely with the farmers who produce it across dozens of coffee-growing communities. For this project, that relationship matters because it means all four coffees begin with the same carefully sourced harvest. The starting material is consistent, so we can focus on processing and fermentation rather than wondering whether differences in origin or raw material drive what we taste.
Chris from Bell's Beans supplied the coffees and handled the roasting and shipping for this project. Having the coffees roasted specifically for the project means we can find out what all this fermentation theory actually tastes like.
For now, we’re still learning and still have plenty of questions. On 3rd October, we’ll sit down, taste the coffees, and see what we can learn from what’s in the cup.
