Coffee fermentation sparks mixed feelings—some hate it, others love it. But there’s no denying that it’s becoming a hot trend in coffee processing. So, what exactly is fermentation? How does it enhance coffee quality? And can coffee be processed without it? To find out, I interviewed Carlos Guiraldeli, Post-Harvest Coordinator at O’Coffee, a Brazilian farm known for its direct trade specialty coffees. He’s leading an experimental program to understand the impact of fermentation on coffee quality.
Unlocking the Mystery of Coffee Fermentation: What Is It?
Let’s revisit a bit of high school science: fermentation is a chemical process. When yeast, bacteria, and other microorganisms interact, they break down substances—usually sugars—into simpler components. This process often generates heat, and enzymes can speed up the reaction. In simpler terms, fermentation occurs naturally when sugar meets water—and coffee cherries are packed with both. As soon as the cherries are harvested (and sometimes even before, depending on humidity), fermentation begins.
How Does Fermentation Impact Coffee?
Fermentation plays a crucial role in post-harvest coffee processing, and it can occur in two distinct ways:
1. Aerobic Fermentation: This takes place when oxygen is present. It’s straightforward—simply place the freshly picked cherries in a tank or container and let the microorganisms do their job. Time and temperature are monitored to control the process.
2. Anaerobic Fermentation: Here, the cherries are submerged in water inside a tank (either before or after pulping). This environment allows different microorganisms to thrive and work.
So, what’s the difference? According to Carlos, “Anaerobic processes are more consistent and easier to monitor, while aerobic ones are more varied and complex to oversee.”
You’re not limited to choosing just one method. At O’Coffee, Carlos shares that they experiment with both aerobic and anaerobic processes—and sometimes even combine them, starting with aerobic fermentation and finishing anaerobically. There are countless ways to approach fermentation, and the more we explore, the more insights we gain into enhancing coffee quality.
How Fermentation Transforms Coffee Quality
Because Coffee Fermentation is such a complex process, the results can vary widely. If it’s not properly controlled, it can introduce undesirable flavors, like moldy or chemical notes. When done right, fermentation enhances the coffee’s natural qualities. Carlos explains that at O’Coffee, they experiment with fermentation to “expand their range of products and offer clients unique, exotic flavors.” This process allows them to refine the sweetness, acidity, and body of their coffees while adding distinct flavor notes such as fruits, caramel, and chocolate.
As Dr. Britta Folmer notes in *The Craft and Science of Coffee*, underwater fermentation can enhance acidity and aroma while reducing astringency. Meanwhile, pulped naturals or honey-processed coffee, which combine wet and dry methods, may allow for a mild degree of fermentation during the drying phase, producing sweeter flavors similar to natural processing. However, caution is needed. Carlos warns that “over-extended fermentation can lead to a significant loss in sensory quality, diminishing key attributes like acidity, body, and sweetness.”
How Does Coffee Fermentation Work?
Coffee producers have numerous options when it comes to fermentation, and with its growing popularity, there’s still much to learn through experimentation to improve quality.
At O’Coffee, Carlos describes their process:
“For naturally processed coffees, we place the cherries in fermentation tanks with a 5,000-liter capacity, made of masonry and coated with tiles.” This is where aerobic fermentation occurs.
“For pulped coffees, we use ecological depulpers without water, which helps retain as much mucilage on the parchment as possible. These coffees are then transferred to the fermentation tanks, where they stay for variable periods depending on the environmental temperature.”
So, what happens once the cherries are in the tanks?
Carlos elaborates, “For all types of fermentation—whether aerobic, anaerobic, or mixed—the time ranges from 16 to 25 hours. We consider the process complete when the Brix reading (a measure of sugar content) reaches 8°Bx (8 grams of sucrose per 100 grams of the sample) and the pH is controlled around 4.5, ensuring it doesn’t drop below that.” Each method yields different results. According to Carlos, “Natural processed coffees generally score about three points higher in cupping than pulped ones. Beyond the score, the complexity of these coffees is also significantly enhanced, with richer and more intricate flavor profiles.”
Consistency and Fermentation: Partners or Opposites?
Great coffee isn’t just about achieving high quality—it’s about maintaining that high quality consistently. This provides assurance not only for buyers and roasters but also for the producers themselves. Carlos explains that while it’s difficult to fully predict the outcomes of coffee fermentation experiments, there are methods to improve the consistency and repeatability of the results.
Producers need to understand the intricacies of Coffee Fermentation to make informed decisions. Training in quality analysis, such as cupping, is essential so they can assess the effects of their experiments and make adjustments when necessary. A deep knowledge of their processes, paired with precise execution, helps ensure both quality and consistency. Clean equipment is crucial, and detailed data collection throughout and after fermentation allows producers to understand, control, and replicate their methods.
Carlos emphasizes the importance of monitoring variables like Brix levels, pH, fermentation time, and temperature. By cupping the coffees, producers can gather valuable insights. The more information they have, the better they can use fermentation to consistently produce top-quality coffee.
If mishandled, fermentation can result in poor outcomes for producers. But when done right, it creates delicious, unique coffees that consumers crave. Ultimately, fermentation is inevitable—it’s up to producers to decide whether to restrict it or fully embrace its potential.
