The Fermentation Situation
Written by Covoya Junior Coffee Trader Ana Mallozzi, this article originally appeared in Barista Magazine and is reprinted with permission.
When someone’s interest in specialty coffee sparks, they’ll quickly come across the word “fermentation” when they begin learning about coffee processing. It is probably fair to say that most people are familiar with the word. Historically, most cultures have created and consumed foods and drinks that undergo fermentation—and they continue to do so. The basic principles behind fermentation apply to all, but when we think of fermented foods and beverages—bread, kefir, beer, chocolate, kombucha, tofu—it’s striking how different they taste.
In the coffee world, we’re hearing about coffees undergoing anaerobic fermentation, fruit fermentation, and even koji mushroom fermentation in post-harvest processing. Experimentation with fermentation in coffee processing will continue to grow in the industry, and the subject is complex enough to warrant thorough exploration. On that note, let’s begin by taking a big step back in our effort to better understand fermentation and how it applies to coffee as well as a few other consumables for context. We acknowledge that the readership of Barista Magazine is vast, and everyone reading this article will have different experiences and expertise with the topics mentioned. The goal of this article is to cover the basics. Fermentation in coffee is an expansive discussion, and it’s important to lay some groundwork on which to build with more specific articles in the future.
What is Fermentation?
Famed Danish chef and restaurateur René Redzepi and fermentation expert David Zilber, authors of The Noma Guide to Fermentation, say at the most basic level, “fermentation is the transformation of food by microorganisms.” Fermentation is an organic and ever-present part of life. Thousands of years ago, cultures around the world that had no connection to each other started noticing this strange phenomenon that was spontaneously transforming food items around them, and independently developed ways to harness that power. It can’t be stressed enough that the ability to preserve and modify food by controlled fermentation is recognized as a pivotal component in the story of humanity.
“It is no accident that the word ‘culture’ has such a broad connotation,” says Sandor Ellix Katz, author of Wild Fermentation, a go-to source for those interested in the topic. “Fermentation cultures are cultivated no less than plants are cultivated, and for that matter no less than ‘the socially transmitted behavior patterns, arts, beliefs ... and all other products of human work and thought’ that constitute the dictionary’s first definition of culture.”
Bacteria and yeast are the microorganism powerhouses at work in fermentation and are intertwined with all of life as we know it. If you are someone like me who might need a refresher from bio 101, let’s reacquaint ourselves with these co-stars of the show.
Bacteria are found in every habitat on Earth and in all living things. In the oceans of planet Earth 3.5 million years ago, bacteria were among the first forms of life to emerge, and oxygen-producing bacteria are what created our atmosphere. Needless to say, humans and bacteria have relied on each other since the beginning of time. Although we usually hear about bacteria as it pertains to disease, it’s important to remember “there are billions of beneficial bacteria living on and inside of us. At the end of the day, the majority of them are harmless to us” (Redzepi & Zilber, 2018). The most well-known bacteria that plays a role in fermentation is Lactobacillus, which produces lactic acid. Lactobacillus may ring a bell: It’s an important bacteria for our gut biome, and one of the reasons certain fermented foods are said to provide health benefits—especially for the digestive system.
Yeast’s scientific name, Saccharomyces cerevisiae, literally means “sugar-eating fungus.” Like bacteria, wild yeast is all around us. There are 2,000 known strains of yeast, and it’s possible to purchase specific strains (or “commercial yeast”) to better control processes and replicate desired outcomes. You can imagine using commercial yeast “as akin to getting a purebred dog: you know exactly what you’re getting every time. Wild yeasts … are like a feral and undomesticated relative of the dog—they interact with other organisms in their ecosystem, have many more flavors, and are harder to control” (May, 2020). This isn’t to imply one type is better than the other; they both have their benefits depending on the application.
As inextricably connected as our relationship with these microbes is, the same can be said for their relationship with one another. In fact, the way bacteria and yeast work in harmony with each other is what makes organic matter ferment into another edible food item as opposed to decomposing. Both “fermentation” and “rotting” are defined by microorganisms transforming food. Fermentation is considered a controlled process that discourages the growth of harmful bacteria and allows good bacteria to flourish. “Rot is a club where everyone gets in: bacteria and fungi, safe or unsafe, flavor enhancing or destructive. When you ferment something, you’re taking on the role of the bouncer, keeping unwanted microbes out and letting in the ones that are going to make the party pop” (Redzepi & Zilber, 2018). One example of an effervescent party is a type of fermentation used for foods and beverages around the world: lacto-fermentation.
Carbohydrate-rich foods like fruits and grains have high amounts of sugars like fructose and glucose. Yeast eats fructose and glucose and produces ethanol (alcohol) and carbon dioxide as a byproduct. Ethanol creates an acidic environment that Lactobacillus bacteria love, but that is toxic to other potentially harmful bacteria. Lactobacillus happily eat simple sugars present, converting them into oxygen for themselves with a waste product of lactic acid. Lactic acid helps preserve the food (and imparts the tangy flavor you may be familiar with) without needing to compete with other harmful bacteria. Depending on what’s being fermented and the desired result, the processes that might follow from here are many: Bread, sauerkraut, yogurt, and injera are all examples of lacto-fermented foods.
Another critical component of fermentation is oxygen. When fermentation occurs in the absence of oxygen, it is referred to as anaerobic fermentation. In lacto-fermentation, there is no oxygen present for the microbes to consume, so the yeast and bacteria perform anaerobic respiration to break down sugars and generate energy to survive. This anaerobic fermentation results in lactic acid, CO2, and sometimes ethanol.
Conversely, aerobic fermentation takes place when oxygen is present. Open-air conditions introduce airborne microbes that can interfere with the fermentation, making aerobic fermentation more difficult to predict or manage, but this is not necessarily a bad thing.
The standard way to brew kombucha is a great example that uses both processes. The initial ferment of kombucha begins as an aerobic process. The bacteria and yeast that make up the gelatinous, microbial culture used to create kombucha (called a SCOBY) need oxygen for their metabolic processes to occur. Once the beverage is properly fermented to taste, the SCOBY is removed, and the kombucha begins a second anaerobic fermentation under airtight conditions. The absence of air allows the bacteria and yeast to go through different metabolic processes, like creating CO2 for a bubbly beverage.
Fermentation + Coffee
The fruit of a coffee cherry contains sugar. Coffee is grown, harvested, and usually processed outdoors, where wild microorganisms abound. Therefore, fermentation or rotting of the fruit is inevitable, and can start as soon as the cherry is picked (and sometimes before). Working with naturally occurring fermentation was, and continues to be, a way to break down the fruit of a coffee cherry so it can be detached from the seed (or bean) more easily. This aids in the post-harvest process of stabilizing the coffee beans in preparation for storage, shipping, or roasting. Other beverages, such as wine, kvass, or tepache, require successful fermentation for transformation of the ingredients they start as to the state we know them in. Coffee is different because fermentation that occurs in the fruit lends characteristics in the final brew, but the beverage that’s consumed does not undergo fermentation.
Fermentation is one of many steps of post-harvest processing. Depending on multiple variables, like the region, weather, and the post-harvesting method implemented, a diverse amount of microbial activity will happen in the flesh of the coffee fruit. Processing, which includes fermentation, is a way to control some of the microbial action. Traditionally, the decision on how to treat coffee during post-harvest processing was not based on the cup profile one wanted to attain, but by the resources available. Over the years, processing has become a tool to purposefully influence the final cup. Green coffee beans are porous, and they will absorb the effects of the post-harvest treatment they receive, including during the fermentation stage. Choices can be made when fermenting coffee beans to attempt to achieve favorable characteristics, like fruity flavors, high acidity, or a distinct mouthfeel.
Over the past decade, the specialty-coffee industry has seen exponential growth in different types of post-harvest processing being used, with much attention given to the fermentation. Many of these methods derive from the same foundational processes that we’ve covered above. Anaerobic fermentation, for example, is fermenting the coffee cherries in the absence of oxygen to encourage different metabolic activity. Both whole and pulped cherries can be fermented this way. It will affect the flavor profile of the coffee, but in some cases, it may also make the desired outcome a bit more predictable and easier to manage. Open air can add microbes or change the metabolic process during fermentation, so by putting the coffee in a covered, airtight container, it’s taking that component out of the equation. A tremendous amount of time and hard work is going into exploring and collecting data about the fermentation stage of post-harvest processing, and now that we understand the basics of fermentation, we’ll be able to focus solely on this topic in a future article.
Fermentation in Other Foods + Beverages
However different the outcome, all foods and beverages that undergo fermentation have the same variables that affect the process and the taste of the final product. It’s important to note that having control over certain variables was generally not possible in the past without the available technology of today. In much of the coffee-producing world, challenges persist, as coffee processing is intrinsically connected to the environmental conditions of the region and the resources available to coffee producers. Fermented food and drink, especially when produced in commercial kitchens, are crafted in strictly regulated conditions. Variables such as time, temperature, and humidity are all crucial in influencing microbial activity and the outcomes. Knowledge of how fermentation applies to other things we eat and drink can be immensely helpful in understanding newer techniques being used in the specialty-coffee industry. We reached out to a few local businesses to become more familiar with how fermentation applies to what they make. Each product uses a different type of process, whether it’s the use of salt, a starter, or heat to initiate, and in some ways control, the fermentation process.
Kimchi
“Kimchi is one of the oldest fermented foods around. It’s been made for a thousand years using the amazing power of salt combined with vegetables,” explains Minnie Luong, co-founder of Chi Kitchen in Pawtucket, R.I. Kimchi is traditionally made with cabbage, though you can use other vegetables along with ingredients like gochugaru, garlic, and ginger. For kimchi, the vegetables undergo lacto-fermentation when added salt turns their environment acidic. “When you add salt to vegetables, it sets up a competition between good bacteria that exists on the vegetables,” Minnie says. “The salt inhibits the growth of unwanted organisms, allowing the Lactobacillus to flourish.” There is a learning curve when making kimchi, but once you have the hang of it, there’s lots of flexibility to explore different flavor profiles. “Keep in mind the kimchi will become more acidic once it’s fermented, so we [at Chi Kitchen] always try to balance acidity, salt, and spice.”
Sourdough Bread
“There is a bit of give and take when you work with bread, something that is alive, because it does have its own agenda and lifecycle,” says Melissa Denmark, a farmer and baker at Moonrose Farm in Rehoboth, Mass. Sourdough bread is defined using a starter made from wild yeast as the leavening agent, where other breads use commercial yeast to prompt the dough to rise. The starter is a “healthy, bubbly yeast colony” made from a mixture of flour and water. The starter is kept at room temperature and is fed daily with new water and flour. You’ll start to see pockets of air in the starter, as the wild yeasts in the flour eat the sugars and produce CO2. This yeast activity also creates great living conditions for lactic acid bacteria, which give sourdough its signature flavor. A properly cared for starter can live for hundreds of years, and it will ferment differently as it becomes stronger. Melissa suggests trying out different flours, like sprouted grains, which contain many more microbes than commercial flour, as another way to play around with fermentation.
Spirits
“Fermentation is the most crucial step in the production of alcohol,” says Eric Olson. A longtime home beer brewer and hops grower, Eric is the co-head distiller at The Industrious Spirit Company (ISCO) in Providence, R.I. The first step in neutral grain spirit production is making a mash by cooking whatever ingredients the maker chooses as their base that contain carbohydrates or sugars (whether it’s grains, potatoes, or even hemp seeds) in hot water. This aids in the breaking down of the carbohydrates into simple sugars. Then yeast is added and creates alcohol and carbon dioxide as a byproduct. “After about a week, the yeast will end its life cycle and flocculate out of suspension, falling to the bottom of the tank and leaving behind a boozy mixture,” Eric says. This initial process is similar to how a 9% ABV beer might be made, but the continued distillation and redistillation will turn this liquid into something much different: a neutral grain spirit. “While some ‘cleaning up’ of off flavors is possible through the distillation
process, it’s impossible to make a good spirit from a bad ferment,” adds Eric. ISCO currently makes their spirits from a malted corn base, although Eric notes that different base ingredients and yeast
strains, along with time and temperature, will impact the final beverage.
Whether it’s via an exciting new coffee, familiar spirits in a go-to cocktail, zesty pickles in your lunch, or a crusty loaf of bread at home, fermentation is an integral—though quiet—part of our everyday lives. With some foundational groundwork laid, hopefully we’ve demystified how fermentation works, piqued your curiosity, and given you confidence to strike up a conversation about new processing methods with your barista, roaster, green buyer, or whoever your source may be!
Sources
May, Mary. (2020, Dec. 6). “Wild Fermentation.” Science in the News. sitn.hms.harvard.edu/flash/2020/wild-fermentation
Bacterial World. (n.d.) Museum of Natural History, University of Oxford. oum.ox.ac.uk/bacterialworld
Sheehan, Jessie. (2021, July 8). “What is Yeast?” Food Network
Cooking School. What Is Yeast? | Cooking School | Food Network
Katz, Sandor Ellix. 2016. Wild Fermentation: The Flavor, Nutrition, and Craft of Live-Cultured Foods. Chelsea Green Publishing
Redzepi, René and Zilber, David. 2018. The Noma Guide to Fermentation. Artisan Publishing
Peter, Michael. (2022, Dec. 11). “Aerobic vs. Anaerobic Kombucha
Fermentation.” Raw Brewing Co.
kombucha.com/aerobic-vs-anaerobic-fermentation
