FERMENTATION AND COFFEE, PT. 1
Fermentation isn’t just for making pickles; actually, every coffee that makes its way to your cup has been fermented in some way. We utilize fermentation to get to the seeds of the coffee cherry - the beans - but that’s not all. Any act of fermentation adds flavor, good or bad. Let’s take a look at how fermentation affects the flavor of our coffee, and why we use it in the first place.
Broadly speaking and at its most basic level, fermentation is the transformation of for by microorganisms (bacteria, yeast, fungi). More specifically it’s the transformation of food through enzymes created by those microorganisms, and even more specifically, it’s the process by which those microorganisms convert sugar into another substance in the absence of oxygen. It’s one of the oldest and most reliable methods of preserving food, and you likely have many fermented products in your home right now: pickles, kimchi, yogurt, sour cream, sauerkraut, beer, wine, and even sourdough bread. There are a lot of biological processes happening, but the most important ones from a taste perspective are those that break down long chains of molecules into smaller parts (i.e. amino acids and sugars). There’s a thin line between fermentation and rot, and the fermenter’s job is to control which microbes thrive.
All coffee is fermented - and fermentation in coffee is the method by which we remove mucilage (slimy fruit material) from the seed. It’s the cheapest, fastest, and simplest method to achieve these results. It’s best to think about coffee processing in three steps rather than classifying it by its fermentation style (ex. fully washed, anaerobic, natural, etc.):
What we do with the coffee pre-ferment (de-pulp, wash, etc.)
Fermentation
Drying
Taken together, these three steps will give us a fuller and more accurate picture of the coffee.
in naturally processed coffees, the process of mucilage breakdown is more complex and less understood than in washed coffees; in fact, the microorganisms involved weren’t isolated until 2008. At first bacteria dominate, but as the cherries begin to dry the bacteria can’t reproduce, leading to the rise of yeasts and fungi. Over-fermented or “off” flavors can develop easily if the coffee is not raked constantly to allow equal access to airflow.
In washed coffee, there is no standardized vessel for fermentation, though large concrete or tiled tanks are most common. Most fermentations are open air and in water, although neither is strictly necessary. As the microorganisms break down sugars, they create acid. The acidification of the water leads the mucilage to break down. Most are wild fermentations, meaning the flora involved are naturally present on the skins of the fruit, in the water, in the air, and on the walls of the tank. Fermentations can last anywhere from 6-72 hours and beyond; coffee is held in the tanks until the mucilage has been completely dissolved, often tested by inserting a paddle or hand into the coffee and seeing if any of it sticks.