We all know that different processing methods bring a rich variety of flavors to coffee. For example, Front Street Coffee's bean list alone features dozens of varieties, covering more than ten different processing methods. Today, Front Street will focus on four processing methods—wet-hulled, semi-dry, pulped natural, and honey—and explain their processing steps, characteristics, and main differences.

First, let's look at the structure of a coffee cherry. From the outside in, a coffee fruit can be roughly divided into the outer skin, pulp, mucilage layer, parchment/hull, silver skin, and the coffee bean seed at the very center. These processing methods are essentially different ways of removing the skin and pulp to extract the coffee bean seed inside.

Wet-Hulled Processing

Wet-hulled processing is a fairly common method in Sumatra!

When the bean is still moist and soft with a moisture content as high as 30–35%, the parchment layer is removed, exposing the surface of the green bean directly, and then drying continues in order to solve the problem of excessively long drying time. Because this method shortens the drying time to just two to four days, the fermentation period of the coffee beans is shortened and the acidity drops considerably, while the body increases relatively. Caramel and fruity notes become prominent, sometimes with herbal or grassy aromas and woody notes—this is Sumatra's distinctive "taste of place."

This processing method exists mainly because Sumatra's climate is humid, so it was developed to suit local conditions, with the goal of speeding up drying.

1. Sorting

The coffee fruit is depulped, and the parchment beans are placed in a large bucket or tank filled with water, where defective floating parchment beans are skimmed off the surface.

2. Fermentation

The dense parchment beans that sink to the bottom are rinsed briefly, then taken out and placed in a bucket or plastic bag for a short dry fermentation—that is, allowing the mucilage sugars on the surface of the parchment to ferment and enhance flavor. Basically, the longer the fermentation, the heavier the acidity. Fermentation time varies from person to person and is generally just a few hours, but some estates skip the dry fermentation stage and directly sun-dry the parchment beans, which can preserve acidity and increase the syrupy mouthfeel, allowing the mucilage sugars to ferment fully and enhance flavor. Fermentation usually lasts between 12 and 36 hours, depending on the specific circumstances.

3. Hulling and Drying

The parchment beans are sun-dried for one to two days until the bean moisture content reaches 30%–50%, while the beans remain half-hard and half-soft. A huller is used to scrape off the parchment, and then drying continues to speed up the process. After about two days, the moisture content reaches 12%–13%, and the coffee beans are collected into woven bags, usually in 40 kg and 80 kg bags, and sent to a coffee processing plant for hulling. At this point the process is complete, taking about four days in total.

The hulling process uses a huller to grind off the bean shell, followed by further drying until the moisture content reaches about 12%–15%. The coffee beans are then sent for machine sorting to remove various impurities, and then classified by bean size.

However, wet-hulled processing does have certain drawbacks. During the hulling process, the temperature of the coffee beans can rise to 30–60°C, and the parchment is completely destroyed, which may trigger germination of the beans. There is also the issue that because the fruit skin is removed during processing, the beans come into direct contact with the air, so moldy and other defective beans are far more common than in washed or natural methods.

The effect of removing the parchment early is that halfway through drying, the green bean has lost its last two protective layers (note: coffee beans have four protective layers: fruit skin, mucilage, parchment, and silver skin), which is like stripping off your clothes to sunbathe. Although wet-hulled processing solves the problem of drying time, the relative risk of the green beans being contaminated by mold, fungi, and yeast also increases greatly. But paradoxically, these very factors become the key to creating Mandheling's distinctive aroma.

Goat-Foot Beans

When talking about wet-hulled processing, one cannot help but mention goat-foot beans! If you look carefully at Mandheling green beans, you will notice quite a few goat-foot beans. Because the half-hard, half-soft moist green beans are easily crushed by mechanical force when the parchment is removed, the beans are prone to cracking into a shape like a goat's hoof. This is why Sumatra has a relatively high proportion of goat-foot beans.

Semi-Dry Processing

This is a method between natural and washed processing, and can be further divided into two types: pulped natural and honey processing. The two are basically very similar—both first remove the outer skin of the coffee cherry as in washed processing, but skip the washed method's "tank fermentation and clean-water rinsing" steps and instead take the beans directly into the sun to dry. Although the methods seem similar, one important difference creates two very different flavor profiles, so they are worth explaining separately.

This method uses far less water than the washed method, and some practices resemble washed processing (removing skin and pulp) while others resemble natural processing (no tank fermentation), so it is also called the semi-washed method.

Pulped Natural

Pulped natural (Pulped Natural) was born in Brazil in 1990. To move away from the long-criticized funky natural coffees while also being unable to solve the water-use problems of washed processing, Brazilians ultimately took a different path, combining washed and natural methods to create pulped natural. Pulped natural reduces water usage and also reduces the influence of the outer skin on the coffee beans, making it a highly cost-effective coffee processing method. Coffee produced by this pulped natural method contains the characteristics of both washed and natural processing. Such coffee has quite good acidity, sweetness, flavor complexity, and aroma; its only shortcoming is that pulped natural coffee does not taste as intense as coffee produced by purely natural or washed methods.

The pulped natural process is as follows: the coffee fruit is first placed in a water tank to remove defective floating cherries, then the skin, pulp, and part of the mucilage layer are removed, followed by washing for one hour. Because the soaking and fermentation time is very short, the mucilage is not easily fully rinsed off, and mucilage still remains on the parchment. At this point, the sticky parchment beans are spread on a drying patio to dry, ideally on well-ventilated African raised beds.

1. Bean Selection

First, the coffee fruit is placed in a large water tank to remove floating fruit, and then the sunken fruit is put into a pulper to remove the pulp. This better removes unripe fruit and, more importantly, ensures that when the coffee beans are sun-dried they are no longer surrounded by pulp but only coated with a layer of mucilage, which is more conducive to controlling the subsequent fermentation process.

2. Drying

The beans are moved to a drying yard to dry, and after about 3 days they can reach a certain degree of dryness.

3. Machine Drying

A dryer is used for further drying until the moisture content of the beans reaches between 10.5% and 12%.

4. Polishing

Finally, before the beans are bagged for export, a polishing process is carried out.

Honey Processing

Although it is called honey processing, this does not mean that honey is added or that it tastes like honey! Today, almost all producing regions in Costa Rica use honey processing. This method is also widely spread throughout Central America. Because the mucilage layer on the surface of coffee beans is extremely slippery and high in sugar, people usually call it "honey." During honey processing, the coffee retains part or all of the "honey" while drying. After the coffee fruit is picked, graded, and depulped, it is placed on drying beds to dry.

Because the mucilage dries quickly, the coffee beans hardly undergo fermentation during the drying process. Coffee beans processed this way have slightly higher acidity than those processed by the natural washed method, but much lower than those processed by washed and natural methods.

Depending on the proportion of mucilage retained and the drying method, it is divided into:

White Honey: 80%–90% of the mucilage is removed.

Yellow Honey: 50% of the mucilage is retained, with no fermentation.

Red Honey: basically all of the mucilage is retained, with no fermentation.

Black Honey: basically all of the mucilage is retained, dried at slightly higher temperatures at low altitude, covered for slight fermentation during the first 24 hours, and then transferred to African drying beds for the remainder of the drying process.

Gold Honey: basically all of the mucilage is retained, dried at low temperatures at high altitude, extending the drying time.

Of course, among the many estates in Costa Rica, there are also standards that separately distinguish various honey processing types based on fermentation time, drying bed thickness, and drying method, but due to space limitations, we can only skip over them here. Therefore, we can also simply understand it as:Pulped natural ≈ honey processing.

Pulped natural ensures much less water use than washed processing while reducing the mold problems that often occur in natural processing of coffee cherries. Because the skin and part of the pulp are scraped off from the beginning, the amount of pulp surrounding the coffee beans is much less than in natural processing, and the "breathability" of the coffee beans is also much better, so the fermentation process under full sun is less intense than in natural processing. Coffee processed by pulped natural tastes much like natural coffee, with a heavy body, lower acidity, and higher sweetness—this is what is called "honey processing."

In Brazil, pulped natural is called Pulped Natural; in Costa Rica, the same pulped natural principle is called Honey/Miel Process, which is the honey processing we are familiar with. Coffee farmers in Central America think the pulp remaining on the parchment is as sticky as honey, hence the name Miel Process, or honey processing.

So if we talk about pulped natural, there is a 99% chance that people are discussing Brazil and Costa Rica. Unlike washed and natural methods, which are found all over the world, pulped natural is a relatively "Regional" processing method. Other producing countries certainly have small experimental estates as well, but they are really not representative.

The above content is compiled by CoffeeHunters, a coffee news website.