The Art of Coffee Bean Processing: Unlocking the Secrets of the Best Methods

Discover the secrets behind the world's best coffee by delving into the fascinating world of coffee bean processing methods. From the mysterious anatomy of the coffee cherry to the innovative techniques that transform it into a perfect cup of joe, this article uncovers it all. Dive into the diverse world of dry and wet processes, explore the enticing Kenya and Monsooned Malabar methods, and learn how producers decide which process to use. Join us on this adventure of coffee exploration where we peek into the future of processing and reveal the tantalizing world of honey processed coffees. Are you ready to take your coffee knowledge to the next level? Let's dive in!

COFFEE BEAN 101

But before we dive into processing, let's start with a mini biology lesson.

You see, the coffee bean is technically not a bean. In reality, it's a seed that develops inside what we call a "coffee cherry."

Technically speaking, coffee farming is actually fruit farming.

Processing involves transforming that fruit into a stable and uniform product ready for export and eventual roasting.

Here's an overview of the typical process:

THE ANATOMY OF THE COFFEE CHERRY

Like most fruits, the coffee berry consists of several layers:

• Skin - This is the outermost protective layer of the fruit, also known as the exocarp.

• Pulp - Made mostly of water and sugar, it's the main part of the fruit, also known as the mesocarp.

• Mucilage - The inner layer of the pulp, sticky and sweet, often referred to as "honey."

• Parchment - The husk that covers the seed (coffee beans), which becomes parchment paper-like when dried.

• Skin - The innermost protective layer around the seeds (coffee beans).

• Bean - The actual seed of the coffee cherry fruit. There are typically two seeds inside.

The 3 Main Types of Coffee Processing

Traditionally, coffee is processed in three ways: washed, natural, and honey. While there are other methods, these are the most common ones. For example, wet hulling is a rare alternative found mainly in Indonesia.

1. Washed Coffees

Washed coffees focus primarily on the bean, allowing you to taste the inner characteristics rather than the outer layers.

A natural or honey processed coffee requires a flavorful coffee cherry. Washed coffees rely on the bean absorbing enough natural sugars and nutrients during its growth cycle. This means that factors such as the variety, soil, weather, ripeness, fermentation, washing, and drying play a crucial role.

Washed coffees reflect both the science of coffee cultivation and the skill of the farmers in shaping its taste. The country of origin and environmental conditions also contribute to the flavor.

This process highlights the true essence of a single origin bean, which is why many specialty coffees are washed.

As Holly from North Star Roasters explains, "Washed Ethiopian and Kenyan coffees exemplify the clarity of flavor that can be achieved with the correct processing."

2. Natural/Dry Processed Coffee

The natural process, also known as the dry process, is a back-to-basics approach that originated in Ethiopia. The fruit is left intact and dried without interference. While it requires less investment, specific climatic conditions are necessary for proper drying.

Over time, natural processing has earned a reputation for inconsistent flavors. This is often due to a mix of unripe and ripe fruit drying together.

However, many experts believe that this process has the potential to produce highly flavorful coffees. With consistency, natural coffees can match washed coffees in terms of clarity and offer unique flavor notes. Brazil is one place where this is happening.

Ben from Gold Mountain Coffee Growers attests to the incredible cupping notes and sweet flavors that nicely processed natural coffees can exhibit.

Furthermore, natural coffee is environmentally friendly.

3. Honey/Pulped Natural Coffee

When done right, honey processed coffee can offer flavors reminiscent of honey and brown sugar. The name comes from the stickiness of the beans during processing. It falls somewhere between washed and natural process, offering fruity but less pronounced flavors. It often has a well-rounded acidity, intense sweetness, and complex mouthfeel.

Costa Rica is strongly associated with the honey process, and subcategories like yellow, red, golden, black, and white honey have emerged in recent years. This process can be highly scientific, as the level of mucilage affects the sweetness and body of the coffee. More mucilage results in a sweeter taste.

Dry Process

Also known as the dry process, natural processing is the most traditional way to process coffee. After picking the coffee cherries, they are spread out in thin layers to dry in the sun. The drying stations can vary, using brick patios or elevated beds that allow air to circulate and ensure even drying. The cherries must be turned regularly to prevent mold or fermentation. Once they are dry, the skin and dried fruit flesh are mechanically removed, and the green coffee is stored and rested before export.

Coffee cherries drying on a raised bed in Kenya. The natural process is prevalent in regions where water is scarce, such as Ethiopia and certain parts of Brazil. The traditional methods have seen little change in recent years.

Dry coffee cherries in a raised bed in Kenya. Natural processed coffees tend to divide opinions among baristas in terms of flavor. Some love them, while others dislike them. Regardless of variety and region, natural process adds fruity and sweet flavors to the coffee. Common flavor notes include blueberry, strawberry, tropical fruits, and honey. On the flip side, there can also be wild, fermented flavors and alcohol-like notes. Compared to washed coffees, naturals often have flavors reminiscent of red wine. While natural processed coffees can introduce consumers to unique tastes, they may not appeal to those who dislike wild and fermented flavors.

Wet Process

The wet processing method, known as washing, involves soaking the coffee cherries to facilitate fermentation and separate the cherry from the bean. Alternatively, a mechanical pulper can be used to remove the coffee cherries. Afterward, the green coffee beans are washed to remove any residue and then dried on patios or beds. The resulting coffee has a more "pure" flavor, unaffected by the coffee cherry.

Kenyan Processing

Kenyan coffee is known for its clean taste. It is famous worldwide for its high acidity, clean flavors, and distinctive notes of apple, blackberry, and tomato. This is partly due to the unique Kenyan coffee varieties, SL28 and SL32, as well as the special processing methods used in the country.

The Kenyan method, often called double fermentation, involves soaking the beans to remove any remaining pulp residue. The beans are then washed and rinsed. Next, they undergo a second fermentation in a separate tank for 12-24 hours, this time with less sugar. After another wash and soak, the beans are dried in two stages, with a rapid drying followed by a slower process. Once the moisture content reaches around 11-12%, the coffee is ready to be milled.

Wet Hulled & Giling Basah

A female farmer from Sumatra uses the traditional giling basah (wet hulled) method to process coffee. This method contributes to the unique flavor of Indonesian coffee.

Wet hulling, or giling basah in Indonesian, is the primary processing method in Sulawesi and Sumatra, the largest coffee regions in Indonesia.

While wet hulling may resemble the washed method, the flavors produced are quite different. In the specialty coffee world, wet hulling is not highly regarded. It's like adding ketchup to a prime Kobe steak.

The process begins with smallholder farmers depulping the cherry and fermenting the beans in whatever containers they have available. After a day of soaking, the beans are washed to remove any remaining mucilage. They are then sun-dried for 2-3 days until the moisture content is around 20-24%.

Next, the farmers sell the beans to middlemen who wet hull them immediately using specially designed machines. These machines are powerful and can potentially damage the beans.

MONSOONED MALABAR COFFEE

Monsooned Malabar coffee is an old-fashioned processing technique that still finds its way into espresso blends occasionally.

The process originated on the Malabar coast of India, where it took months to ship coffee beans to Europe. During the journey, the beans were exposed to various weather conditions, including monsoons, which gave them a distinct flavor. However, as transportation improved and the journey became shorter, customers began to miss the unique "monsoon" taste, leading to the development of a new processing method.

This process involves picking the coffee beans, sun-drying them in large barbecues, and sorting them into two grades: 'A' and 'AA'. From June to September, the beans are exposed to constant monsoon moisture in well-ventilated warehouses, where they are turned and raked regularly. This extended exposure to moisture causes the beans to swell and turn pale gold.

However, due to the low pH level resulting from the moisture exposure, most specialty coffee consumers tend to avoid this type of coffee.

NATURAL (DRY) COFFEE PROCESSING METHOD

The natural (dry) processing method is the oldest way of processing coffee, commonly used in arid countries like Western Ethiopia.

In this method, the cherry-like fruits are picked when perfectly ripe. The cherries are left intact, allowing for natural fermentation and the absorption of enzymatic by-products from the mucilage into the seeds (which become the green coffee beans we roast). This process imparts a distinctly unique flavor profile to the beans.

Roasting

Coffee roasting machines

Roasting coffee requires skill and the right equipment, such as a quality coffee roaster. Common machines use propane gas as the heat source, with an electric drum to drive the roasting process. Roasting temperatures typically range from 370°F to 540°F (188°C to 282°C).

Roasting times can vary from 12 to 30 minutes, and the beans shrink by about 20% in weight as they develop a dark color and aromatic fragrance. Approximately 25 pounds of green coffee beans take around 15 minutes to roast, yielding about 1 pound of roasted coffee (100 pounds of coffee cherries yield approximately 12 pounds of roasted coffee).

Fluid bed roasters

A fluid bed roaster is a type of coffee roaster that uses hot air to agitate and roast the green coffee beans. It operates similarly to a popcorn popper.

Roasting time

The total roasting time depends on various factors, including the quality and moisture content of the coffee beans, as well as the desired roast level (light, medium, medium-dark, or dark). The age of the beans and the environmental conditions during roasting also play a role.

Roastmasters carefully manage the roasting time and temperature, paying attention to the appearance and fragrance of the beans. They listen for specific cracking sounds that occur at different stages of roasting.

Grinding

Once the coffee beans have been roasted, they are ready for grinding and brewing.

Grading coffee

The grading process is aided by screens with graduated hole sizing. Vibrating air tables are also used to separate beans by density and remove defective beans that can affect the taste of the final product.

Coffee silverskin

Some coffee processors leave the silverskin (thin outer skin) on the green coffee beans, as it acts as a protective barrier. During the coffee roasting process, the silverskin naturally crumbles off as chaff. Other processors choose to remove the silverskin.

Other processing methods

Anaerobic

Anaerobic fermentation is a relatively new coffee processing method gaining popularity, especially in high-end specialty coffees and competition coffees. This method is similar to the washed process, but it takes place in sealed, oxygen-deprived tanks. Anaerobic processed coffees often exhibit wild, complex flavors.

Carbonic Maceration

This method, borrowed from winemaking, involves fermenting the cherries as a whole. It breaks down the cell walls from the inside out, infusing the beans with intense and unique flavors such as red wine, whiskey, banana, and bubblegum.

Giling Basah

Giling basah, meaning "wet hulled" in Indonesian, is a processing method specific to Indonesia. It is similar to the washed process, but the beans are dried to a moisture content of 30-35% (compared to 11-12% in the washed process). After initial drying, the parchment is removed, and the "naked" beans are dried further until they reach the desired dryness for storage. Giling basah coffees often exhibit earthy flavors like wood, spices, mustiness, and tobacco, which may not be highly appreciated among coffee professionals.

Demucilaging, drying, and hulling

The first step in the coffee processing involves removing the mucilage from the coffee cherry. This is done through a process called fermentation, where the cherry is placed in a fermentation tank for 12 to 24 hours.

After fermentation, the coffee beans are dried. There are two methods for drying: forced-air drying or natural drying in the sunlight on decks or patios. Once the drying process is complete, the moisture content of the coffee beans is usually around 10.5%.

Hulling, also known as husking, is the next step. This is done using a machine called a huller, which removes the parchment and silverskin from the beans. It also polishes the beans, which are now referred to as green coffee beans, as they have been milled but not yet roasted.

Aquapulp coffee processing

Aquapulp is a method of removing the sticky pulp, or mucilage, from freshly-picked coffee cherries. This is achieved through mechanical demucilaging, which involves the use of machines to scrub the cherries.

The aquapulp process has become a popular alternative to traditional wet processing methods, such as fermentation and washing, for removing the mucilage.

After the parchment is removed, the coffee beans are sorted and graded based on local standards. The grading takes into account factors like size, shape, and quality. (For more information, see "Grading Coffee Beans".)

How Do Producers Decide What Process to Use?

Coffee producers strive to produce the most profitable and best-tasting coffee possible, but their decisions are influenced by environmental factors. Coffee is particularly susceptible to its surrounding environment.

Producers consider the amount of rainfall before choosing a processing method. Heavy rain makes it difficult to produce good natural-processed coffee, as the cherries can split. Dry conditions are ideal for honey or natural process, as it preserves the sugars.

Some producers, like Gold Mountain, use refractometers to measure sugar content and determine if it's suitable for natural or honey processed coffee. They also aim for high sugar content in their washed coffees, as it results in a sweeter cup.

Experiments & Innovations: The Future of Coffee Processing

Traditionally, coffee-producing countries favored one processing method, such as the washed process in Rwanda and most of Central America, or the honey or natural processes in Brazil. However, the demand for specialty coffee has led to a shift in processing techniques.

Farmers in Nicaragua, Guatemala, and Rwanda, among other regions, are experimenting with natural and honey processes to create unique flavors that add value to their coffee. This experimentation extends beyond processing methods, with some producers exploring oxygen-free fermentation and the use of catalysts to speed up fermentation. Environmental impact is also being considered, leading to efforts to reduce water usage during processing.

Through machinery advancements and knowledge-sharing, producers are able to create more distinctive cup profiles. This demand for experimental processing methods means we can expect to see further innovations in the future.

Hand holding differently processed beans and cherries. Credit: Virginia Coffee Roasters

Coffee processing plays a significant role in shaping the flavor and character of your cup of coffee. Whether it's a honey-processed Costa Rican or a natural-processed Nicaraguan, understanding the processing method allows you to anticipate the unique qualities of each coffee.

Special thanks to Gold Mountain Coffee Growers, Falcon Specialty, and North Star Roasters.

Processing in the future

In the past, the washed process was considered superior due to its "clean" taste and ability to sort out defects. However, with the demand for novel flavors in specialty coffee, innovative farmers are integrating agricultural science into their processing methods.

Specialty coffee consumers and emerging markets in Asia are driving this change, as demonstrated by the increasing preference for natural-processed coffee in competitions like the World Brewers Cup. Carbonic maceration, an innovative processing technique, was also used by the 2018 competition winner.

As our understanding of specialty coffee processing grows, we may start to categorize coffee not just by region or variety, but also by processing method.

Honey Processed Coffees

Honey processed coffee combines elements of both natural and washed methods. While it is less commonly practiced, it produces a unique cup of coffee with flavors similar to both methods. During honey processing, the seed is removed from the cherry with a depulper, but the mucilage, or honey, is not washed off. Instead, it remains on the seed as it dries in the sun. The amount of mucilage left determines the sweetness, and machines can control this. The drying process includes raking and rotating the seeds to prevent mold.

Honey coffees offer varied and complex flavor components. Like washed coffees, they have a cleaner body compared to natural coffees. Honey processed coffees also have richer notes of syrupy sweetness due to the remaining mucilage. The acidity is more pronounced than in washed coffees, but still mellow. For more information on honey coffees, including the difference between black honey and red honey, click here.

When purchasing coffee beans, be sure to pay attention to the processing method, which is usually labeled on the bag. Each method will have a distinct impact on the final brew.

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What happens after the coffee is processed?

After coffee beans have been processed, they are still covered by the parchment layer (unless giling basah processed). The moisture content is now low enough for storage to prevent spoilage. The beans are typically stored in dry warehouses, known as reposo, for 1-2 months before export. Prior to exportation, the beans undergo hulling to remove the parchment. This is done mechanically in a dry mill. After hulling, the beans are graded and sorted based on size and color using machines or hand sorting. They are then packed in jute bags weighing either 60kg or 69kg, depending on the country of origin. These bags are placed in shipping containers to protect the beans during transportation to roasteries.

Graded green coffee in Kenya

Jute bags full of green coffee

In conclusion, the coffee bean processing methods play a crucial role in determining the flavor, aroma, and overall quality of our beloved morning cup of joe. From the traditional wet and dry processes to the specialized Kenyan processing techniques, each method brings its own unique characteristics to the table. And just when we thought we knew it all, innovative experiments like the honey processed coffees are pushing the boundaries of coffee processing even further. As coffee enthusiasts, we can look forward to an exciting future where new processing methods emerge, enhancing our coffee experience and expanding our palate. So the next time you sip on your perfectly brewed cup of coffee, remember the intricate journey it took from the coffee cherry to your mug.