I recently had the pleasure of meeting Lucía Solís, a fermentation expert deeply involved in the wine industry. Lucía has been working in the specialty coffee industry for the past three years as a "coffee fermentation designer": she helps processing plants streamline, improve, and customize their fermentation processes.
The old (and current) view of fermentation is that it offers no opportunities to improve flavor, only risks. The new view (Lucía's) recommends not leaving fermentation to chance but managing it in a way that helps improve the final product while reducing the risk of substandard batches.
Surprisingly, some green coffee buyers have criticized Lucía's work and seem afraid that the intentional design of fermentation will reduce the diversity of available coffee flavors or "spoil" the coffee in some way. Many innovative ideas are a little scary at first, but I will support any proposal that promises to protect coffee farmers from risks, is a small step toward making the profit more predictable, and gives the coffee maker a new tool. I encourage you to read what Lucía has to say and decide for yourself. I'd love to hear your thoughts.
Scott
By Lucía Solís
My work as a winemaker and now as a coffee fermentation manager focuses on a simple truth: fermentation generates chemical components with sensory characteristics.
My initial intention was to focus on microbes because of my background as a winemaker. I earned a degree in Viticulture and Enology from UC Davis and worked for nearly a decade in wineries in Napa Valley, California, before my experience in microbiology and fermentation led me to the world of coffee.
Currently, I travel to coffee processing stations and farms in Central and South America, where I work directly with producers to change the way they process coffee.
Roasters can provide diverse flavors by offering coffees from different parts of the world. This practice emphasizes regional differences that reflect the effects of geography, but minimizes the role of post-harvest processing in flavor development.
Most differences between coffees are usually attributed to varietal, climate, and growing conditions, but the contribution of microbes is often overlooked.
The tiny microbes (yeast and bacteria) that transform the coffee cherry into parchment have the ability to greatly affect flavor. 
The process of converting cherries into green coffee ready for roasting involves several steps, each of which can influence the flavor and quality.
Diagram text:
Cherry: cherry / Pulp: pulp / Full removal: complete removal / No removal: no removal / Partial removal: partial removal / Dry process: dry process / Wet process: wet process / Tank: tank / No tank: no tank / Dry fermentation: dry fermentation / Submerged fermentation: immersion fermentation / Wash: wash / Natural: natural / Pulped natural (honey): Honey / Washed: wash / Mechanical demucilagination: mechanical removal of mucilage / Dry: Dry
We only have a handful of terms to describe fermentation methods—washed, wet, honey, or natural—but each of these terms can encompass very different and complex steps. These steps, and the time involved in what would be described as a "washed" process, vary greatly depending on climate, altitude, varietal, ripeness, tank design, and a host of other variables that affect fermentation kinetics.
A coffee could spend anywhere from 8 to 72 hours in contact with mucilage (fermentation) before being washed. The term “fully washed” doesn’t necessarily imply that a coffee has been fermented. Even if you know for sure that this has happened, a coffee dry-fermented for 8 hours will likely taste different than one fermented underwater for 40 hours; just as if we were comparing one fermented at 700 meters above sea level (asl) at 26°C with one fermented at 1,500 meters above sea level at 12°C, or one fermented in wood with one fermented in ceramic tanks, etc. Not only are the words we use to describe the process insufficiently specific. Furthermore, little is known about the effects of the different process steps on flavor or the microbes involved during those steps. This is the focus of my work.
In order to change the way coffee is physically processed by highlighting the effects of the microbes present, I had to update producers' definition of the term "fermentation." I'd been trying to educate producers about the effects of different strains of yeast and bacteria on flavor, but I wasn't getting anywhere. Ultimately, I realized that few people were initially aware of the value of fermentation.
He used the word “fermentation” to describe a metabolic process through which yeasts and bacteria transform sugars into energy and flavor compounds. The more common definition for coffee is “the step in which coffee with the pulp sits in a tank until the mucilage sloughs off.” It was like trying to teach roasters to roast with a falling RoR and realizing they don’t understand the effect of sensor thickness on the curve. In the wine industry, fermentation is widely studied because it’s a necessary step in making wine: without it, you don’t get the product. I realized that the same term was used in the coffee industry, but it had a very different meaning for almost everyone I spoke to. I think the main reason for this discrepancy is that “fermentation” is optional in coffee; it’s simply a method of isolating the seed from a cherry.
In addition to being optional, it's not limited to a single process as was once thought. Fermentation doesn't only occur in vats with wet/washed coffees; it's also present in honey and dry/natural processes. In all processes that involve fermentation, there's an option to influence flavor. Fermentation begins the moment microbes, which exist on virtually every surface, find an entry point into the fruit. The possibility of fermentation occurs as soon as the fruit is picked or when the skin is damaged (exposed juice) while the cherry is still on the tree.
To manage the risk of spontaneous fermentation in winemaking, some wineries harvest at night (at the coldest time of the day, to slow microbial activity). The grapes are sprayed with sulfur dioxide to limit the population of wild yeasts from the soil, or they are stored in dry ice until they are ready to begin fermentation with known and selected microbes.
Fermentation is a natural process that occurs without human intervention. Winemakers actively decide whether to risk spontaneous fermentation or choose the microbes and control the process. Even if they choose to use wild, non-commercial yeast, they are making a choice that actively affects flavor. Most commercial producers of fermented products (wine, bread, cheese, beer, chocolate) inoculate the fermentation. This is uncommon in the coffee industry because the focus has been on reducing processing risks, and the benefits of the previous point have not been well understood.
Wine, chocolate, cheese, beer, and bread—various products from other industries—take advantage of the action of microbes to achieve desired results.
Things that are fermented on purpose: Foods that are fermented on purpose
The coffee industry defines "processing" or "milling" as the period between cherry harvesting and its transfer for drying, whether the whole cherry (dry or natural process) or the parchment (washed process). The cherry skin acts as a protective barrier for the seed. Therefore, when it is removed, the seed runs the risk of spoilage. Most publications on the subject emphasize the importance of speeding up the process to reduce the likelihood of damaging or reducing the quality of the coffee. Extending the time until the cherry transforms into a dry seed is considered risky in terms of quality. In other words, the traditional paradigm suggests that fermentation offers no options for improving flavor, only risks. 
Traditionally, the transition from coffee cherry to dried green coffee has been fraught with risk. Popular belief has focused on limiting fermentation time to a minimum to reduce the seed's vulnerability. An alternative method is to control and extend fermentation to achieve positive flavor attributes while mitigating risk.
Traditional: Traditional / Alternative: Alternative / Protected: Protected / Stable: Stable / Flavor town: Universe of flavorsAlthough microbes cannot be observed with the naked eye, we know they influence flavor and aroma because we notice their impact when fermentation goes wrong: we notice it through defects in the cup. This explains the push that some experts like Sivetz and Flavio Borem are giving to the mechanical removal of mucilage. According to this approach, processing maintains, at most, the inherent quality of the fruit. 
Flavor metabolites are basically the farts of bacteria and yeast. Which would you prefer to marinate your coffee in?
Coffee marinating in microbe farts: Coffee marinating in microbe farts
But what are the advantages? We know that the process can affect the flavor in positive or interesting ways: this explains the ubiquity of honey-processed coffees and the presence of natural coffees in the coffee market. In other words, we understand that natural coffees don't taste the same as washed coffees, so clearly the process influences the flavor, even if some people reject all coffees processed with a specific method.
Producers can continue to rely on luck or harness the power of microbes that influence cup flavors. Let's not be intimidated: just because more producers are selecting their microbes doesn't mean coffee flavors will become more homogenous. Varietal, sugar and nutrient levels in the fruit, tank shape and material, ambient temperature, water quality, contact time, and other factors will still affect fermentation. This means we're not eliminating flavor diversity but limiting the presence of unwanted flavors.
I reject the view that the process is simply about maintaining quality or reducing defects. I believe there are practices, such as controlled fermentation, that can improve and add value to coffee. If coffee is fermented properly, it becomes a more complex and valuable product than one whose mucilage is mechanically removed. Essentially, fermentation transforms the raw material, creating new flavors.
Like master brewers, instead of waiting a year with an open keg exposed to ambient conditions and wondering whether the result will be delicious or taste like sewage, producers can apply a method like kettle sour to their coffee and consistently achieve the same flavors. We use microbes to break down the nutrients in the mucilage and produce the desired metabolites. We brew a delicious “wort” and let the coffee sit in it beyond the traditional “fermentation” point so the seed absorbs the wort and those flavors. Careful selection of microbes can protect the coffee from spoilage and preselect the metabolic products we want: those that taste and smell good.
Controlling fermentation is key to harnessing the process's potential and achieving positive attributes. Fermentation, a biological mechanism that occurs in all types of processing, gives us the opportunity to influence flavor, and every step from farm to patio can impact coffee quality and consistency. By understanding the power of fermentation and the process, producers and roasters can ensure flavor diversity while improving coffee consistency and quality.
To see Lucía's coffee processing photos, visit her Instagram account @lluciasolis
About Scott Rao
Scott Rao is one of the leading figures in the world of specialty coffee. He is the author of several books, including "The Professional Barista's Handbook," "Everything but Espresso," and "The Coffee Roaster's Companion," all written with the aim of helping the industry pivot toward a more educated and scientific understanding of coffee. He devotes much of his time to consulting coffee roasters around the world, teaching coffee roasting classes, and designing cutting-edge coffee equipment.
At Ineffable Coffee, we've been working with Scott Rao since 2018. His advice and experience over the years have been invaluable. As a result of this collaboration, we're delighted to be able to offer this content in Spanish.
Article written by Scott Rao , originally published in English on his blog and translated by Ana Rubio Ramírez of coffeeandtranslation.com
