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Coffee Fermentation: What is it, and Why Does it Matter?

Fermentation – you may have heard of it in chemistry, or even biology class. Or perhaps you’ve heard of it in relation to alcohol – how sugars ferment with the help of yeast and turn into booze. But did you know fermentation can be one of the most important factors in your coffee’s flavor? A growing trend in coffee processing, coffee fermentation takes beans through chemical changes that not only remove excess materials leftover from processing a cherry’s pulp, they also affect the resulting brew.

Let’s start with the basics: chemically speaking, fermentation is a metabolic reaction between microorganisms like yeast and other bacterias as they break down substances. During fermentation, yeast and bacteria feast on chemicals like sugars and generate heat and sometimes effervescence. Commonly fermented things include wine (in which the sugars in grapes break down and become the alcohol in wine); kombucha (lightly fizzy fermented black or green tea); and soy sauce (fermented soybeans).

When it comes to coffee, we’re less concerned about the byproduct of fermentation (the leftover liquid), and more concerned with the changes to the bean itself. You see, fermentation follows what’s known as “wet processing” of coffee beans. Ripe coffee cherries are picked, then washed and forced through screens to remove the outer skin and pulp. This process removes most of the outer fruit, but leaves some bits stuck on the inner pits of the cherries (which are going to become our coffee beans). This must be removed before the beans can move on to the next step.

To start the fermentation process, all beans really need is water. When the bits of leftover fruit, called mucilage, begin to soak, they naturally start to break down and release enzymes and bacteria. Humidity forms, yeast begins to feast on the sugars in the mucilage, and it begins to fall aways from the coffee cherries, leaving behind only smooth, clean coffee beans.

While it sounds like a simple process, fermentation is notoriously difficult to control. Certain factors, like humidity, the fermentation container, the length of time cherries are fermented, and any additives to the water, can be adjusted experimentally, but microorganisms can’t fully be controlled.

Despite this, it’s agreed that fermentation does affect the flavor of coffee, so many farmers choose to use this method to process their cherries. How exactly do a combination of water and microorganisms affect the end flavor? Well, fermentation produces acids, which combine with the natural acids in coffee beans and result in a cleaner, more refined flavor. How much the flavor is impacted depends on how much fermentation the beans went through, but flavors can become more vivid, complex, creamy, or even sweet.

As the industry embraces more scientific approaches to coffee production, we’ve learned more about fermentation and the variables that can be controlled to make the process consistent. And of course, the more we can understand it, the more we can adapt and control fermentation, and therefore produce even more reliably delicious cups of coffee.

Fermentation - you may have heard of it in chemistry, or even biology class. Or perhaps you’ve heard of it...
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articles brewing basics trends

Arabica or Robusta? A Guide to Coffee Varieties

When you take that first sip of morning coffee, do you ever stop to wonder what’s behind it?

Often, we may know the common qualities of our favorite coffee – the type of roast, the country it came from, maybe if it’s a blend or a single origin – but the full picture of the bean behind the brew is a mystery deeper than its rich dark color. Let’s dive into the beautiful world of coffee beans.

Coffee plants fall under the genus “Coffea,” which defines the more than 120 species as the “coffee genus.” These plants are distinguished as small evergreen shrubs or trees that sprout opposite leaves and what’s known as a “drupe” – a berry that contains two seeds inside, which will later become the coffee beans. Coffee plants are found in tropical forests around the world, particularly in South America, Africa and parts of Asia, and they can live up to 20 to 30 years.

While the exact number is changing all the time, there are around 6,500 species of coffee worldwide, both cultivated and wild. These can be divided into three types: varieties, cultivars, and hybrids. A variety, for the purpose we’ll use it here, is any subspecies of coffee, specifically the ones that grow naturally without human intervention. Conversely, a cultivar is not naturally occurring – they’re the ones that have been cultivated for specific purposes by coffee growers. And finally, a hybrid is a cross between two or more species of coffee – and that can be natural, cultivated, or both!

There are thousands of strains of varieties, cultivars and hybrids but when it comes to the coffee we drink, there’s really only two main species to talk about: Arabica and Robusta. There’s a strong possibility that the coffee in your cup is made up of one of these two, or a blend of both! Arabica makes up nearly 60 percent of coffees grown around the world, while Robusta makes up about 40 percent.

However, Arabica and Robusta couldn’t be more different in their qualities. Originally found in Ethiopia, Arabica is considered superior for one major reason: flavor. Known for its sweet, creamy brews, Arabica beans have notes of chocolate, caramel, fruit, or berries, and are high in antioxidants, sugar, and fatty acids. They’re also lower in caffeine (which helps the flavor), and more acidic than their Robusta cousin.

Robusta, on the other hand, is a sturdy, highly caffeinated bean, but it’s strong jolt gives it a very bitter flavor. Also known as Coffea Canephora, Robusta beans are known to taste earthy or like burnt rubber. But! These beans are around 2.7% caffeine, compared to Arabica’s 1.5%, which not only makes them ideal for instant coffee and espresso blends, it also makes Robusta coffee plants resistant to disease and pests. Robusta was discovered in Sub Saharan Africa, although Vietnam currently produces the most.

These two coffees grow differently, as well  too. Although it’s sweet taste means Arabica beans are in higher demand, the coffee plants themselves are fragile and highly susceptible to coffee leaf rust (CLR). Also, much like blueberries, Arabica coffee cherries do not all ripen at the same time on the plant, so they have to be picked by hand to ensure uniform ripeness for roasting.

On the other hand, as we mentioned before Robusta is, well, robust: the plants are resistant to CLR and pests and are a much higher-yielding crop than its sweeter brother. Robusta also matures faster and is less temperamental (for instance, it can grow in full sunny conditions), so it is a highly cost-effective crop compared to Arabica.

But we can’t ignore that flavor, so despite the fact that Robusta is a stronger crop, Arabica still dominates the global coffee market. Because of this, and in an effort to ensure a stronger future, higher crop yields, and hardier plants, World Coffee Research developed a catalog of Arabica varieties, their qualities, and the ideal factors for their growth. This catalog describes everything from the optimal altitude for a coffee plant to the year it will yield its first crop, allowing farmers to pick plants that are best situated for their environment. It also describes the history of the two main types of Arabica, Bourbon and Typica, which coffee as we know it today descended from, making them the most “culturally and genetically important groups of Arabica coffees in the world.”

On the surface, coffee genetics may not seem like an important factor in your morning brew, but the cultivation of coffee over hundreds of years is what brought the steaming mug before you today. As climate shift and cultures change, coffee cultivation does its best to keep up, and tools like the Arabica Varieties Catalog help ensure a stronger future for our favorite brew. The flavors in your coffee can tell you a story – that’s decades of biology and science brewing in your cup.

When you take that first sip of morning coffee, do you ever stop to wonder what’s behind it? Often, we...
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articles coffee industry

The Life Cycle of a Coffee Bean

You know the result: a steaming cup of coffee, brewed from finely ground, beautifully fragrant dry beans. This is the final stage of a coffee bean’s journey; the cup before you holds thousands of hours of labor and miles travelled across the globe. A coffee bean’s life is the culmination of a global trade, one that begins in a farm and ends in a cup. Let’s take a journey through the life of your coffee.

Coffee beans come to us from the tropical climates of the world. They are grown in approximately 70 countries, primarily in warm equatorial regions. Arabica beans, which make up 60 percent of the world’s coffee production, have strict needs: defined rainy and dry seasons, protection from cold and frost, shaded protection from too much sun and humidity, and slightly higher altitudes. Robusta beans, the other 40% of coffee production, are hardier and will grow in a much wider variety of places, as long as they have adequate sun and water.

An evergreen growing plant, coffee trees range in size from small shrubs to little trees. It takes about three to four years from seedling to a coffee tree’s first harvest, and those are years full of hard work keeping each plant healthy. Coffee plants are susceptible to damage from over 900 insects, as well as diseases like Coffee Leaf Rust. Spraying pesticides or herbicides isn’t ideal, either, as these can damage not only the coffee plants but also the surrounding tropical ecosystems. Farmers must carefully deploy targeted methods to keep pests and diseases from spreading, as well as to keep treatments from affecting otherwise healthy plants.

Harvest is no easy task, either. Much like blueberries, coffee cherries do not ripen all at once on the branch, so specialty coffee must be picked by hand to ensure only the ripest cherries are picked. It takes nearly a year for a cherry to mature from flowering, and each plant will yield about 10 pounds of cherries a year – that’s about two pounds of green coffee beans per plant according to the National Coffee Association.

Coffee cherries are also known as “drupes” – a fleshy fruit with stony pits inside. Each coffee drupe has two seeds inside covered by a very thin layer of skin called “parchment.” The two beans are surrounded by pulp and skin, which must be removed after being picked. There’s two ways to do this: wet or dry processing.

In wet processing, the cherries are submerged in water – any unripe cherries, twigs and leaves float to the surface and are picked out. Then, the wet cherries are pushed through a screen, stripping them of the outer pulp and skin. To remove any remaining pulp, the beans are either fermented and microbes eat the remaining bits, or they are scrubbed by machine to remove any leftover pulp. The beans are then dried and ready for the next stage!

In dry processing, any twigs, debris or unripe cherries are first sorted out by hand, and the remaining ripe cherries are laid out in a single layer to dry in the sun. The cherries are raked or turned by hand to allow even drying, which can take up to four weeks. The cherries must reach the right level of dryness — too wet, and mildew or mold can form; too dry and the beans become too brittle to go through the next stages of processing.

The next step of a coffee bean’s life depends on whether it was wet or dry processed: hulling. The hardened dry cherries must have the leathery pulp removed, while the wet processed cherries still have that thin layer of parchment to be dealt with. Hulling can be done by a variety of machines that rub, shake, or mill the coffee to remove the excess fruit. After hulling, coffee beans are cleaned a final time and are finally ready to be sorted.

Sorting and grading are some of the most important steps in a coffee bean’s life cycle: these steps determine the quality of the final roast. In this step, beans are carefully sorted, either by hand or machine, then graded based on size, defects, and color. Only the finest beans are selected in this process; any beans that are too small, too large, or too damaged get discarded.

Once sorted and graded, it’s time to determine what the end result coffee will be like so the beans can be bagged and distributed to roasters around the world. To do this, coffee professionals like Q-Graders use a process called “cupping,” in which they roast and brew small amounts of beans and get up close and personal with the flavors and aromas the beans produce. The brewed beans are nosed, slurped, and prodded to determine the quality of flavor, which beans can be blended with others or stand alone as a single origin brew, and what the ultimate roasting recommendations will be for the final product.

Our finely sorted beans are now ready for production roasters! This is when the coffee we know and love gets its final flavor and aroma. Roasting the beans changes its chemical composition and releases the beans’ fragrances and oils, called “caffeol,” which is what gives coffee its rich, dark taste and aroma. Once roasted and cooled, beans are destined for a bag, then headed to the final consumer: you!

Before drinking, of course, coffee beans take one final step: grinding. The grind and brew of your coffee bean determines how much flavor will be in your coffee — too little water, and it will be overly bitter and oily, too much and the coffee will be watered down. The size and grade of the grind matters as well, but depends greatly on the brewing method. But! With the right instructions, a finely roasted bean is easy to turn into a delicious brew, and the bean’s journey is finally complete: a dark brew, steaming happily in your mug.

You know the result: a steaming cup of coffee, brewed from finely ground, beautifully fragrant dry beans. This is the...
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