We have only a handful of words to describe processing methods, for example washed, wet, honey, or natural, but each of these words can encompass very different and complex steps. The steps and time involved in what someone would describe as “washed” process vary wildly based on the climate, altitude, cultivar, ripeness, tank design and myriad other variables impacting fermentation kinetics. A coffee could spend anywhere from 8 hours to 72 hours in contact with the mucilage (fermenting) before it is washed. The words “fully washed” might not even mean that a coffee was fermented – but even if you know with certainty that it had been fermented, a coffee dry-fermented for 8 hours will likely taste different from one fermented underwater for 40 hours; or one fermented at 700 meters altitude (MASL) at 80°F versus 1500 MASL and 55°F; or one fermented in wood versus ceramic tanks. And so on.

Not only do the words we use to describe the process lack specificity, there is little known about the flavor effects of different processes’ steps or the microbes involved during those steps. This is the focus of my work.

Before I could change the way coffee was physically processed by highlighting the effects of the microbes involved, I had to update producers' definition of “fermentation”. I had been trying to educate producers about the flavor effects of different strains of yeast and bacteria, but I was getting nowhere. I finally realized few people understood the value of fermentation in the first place.

I was using the word “fermentation” to describe a metabolic process whereby yeast and bacteria transform sugars into energy and flavor compounds. Yet the most common working definition for coffee purposes was “the step where the pulped coffee sits in a tank until the mucilage falls off”. This was like trying to teach roasters to roast with a declining rate of rise and realizing that they don’t understand the effect the thickness of the probe has on that curve.

In the wine industry, fermentation is extensively studied because it is a necessary step in winemaking: you can’t have wine without it. I noticed the coffee industry used the same word, but it had a very different meaning to almost everyone I talked to. I think the main reason for the discrepancy is that “fermentation” is optional in coffee; it’s just one method of isolating the seed from a cherry.

In addition to being optional, it is also not restricted to a single process as commonly thought. Fermentation is not only happening in tanks with wet process/washed coffees, it is an element in honey and dry/natural processed coffees as well. In every process where fermentation occurs there is the opportunity to impact flavor. Fermentation begins the moment that microbes, which exist on virtually every surface, find an entry point into the fruit. The opportunity for fermentation happens as soon as the fruit is picked or when there is damage to the skin (exposing juice) while the cherry is still on the tree.

To address the risk of a spontaneous fermentation in winemaking, some wineries pick at night (the coolest part of the day, to slow down microbial action), spray their grapes with sulphur dioxide to inhibit the wild yeast population coming in from the field, or store picked grapes in dry ice until they are ready to begin the fermentation with known and selected microbes.



Fermentation is a natural process that happens without human intervention. Winemakers actively chose whether they will risk a spontaneous fermentation or select their microbes and control the process. Even if they choose to use wild yeast and not commercial yeast, they are still making a decision that actively impacts flavor. Most commercial producers of fermented products (wine, bread, cheese, beer, chocolate) inoculate their fermentation. Inoculation is rare in the coffee industry because the focus has been on reducing the risks of processing, and the rewards have been poorly understood.