There are about 40 species in the Coffea genus, but only three native species—Arabica, Robusta, and Liberica—truly have commercial value. They differ significantly in appearance, flavor, disease resistance, suitable altitude, and cultivation conditions: Arabica is elegant yet delicate, Robusta is hardy and intense, while Liberica is limited to local trade in West Africa. Starting from botanical characteristics, this article systematically sorts out the origin distribution, climate and soil requirements, the complete cultivation process from sowing to harvesting, and the grading systems formed by various producing countries based on altitude, screen size, and defect bean ratio. Whether you are new to specialty coffee or want a deeper understanding of origin logic, this foundational knowledge will help you more clearly judge the variety and terroir code behind the flavors in your cup. Front Street Coffee will also combine the key points in this article to recommend directions for your daily purchases.

The coffee tree belongs to the Coffea genus in the Rubiaceae family and is an evergreen shrub. Rubiaceae plants are mainly distributed in tropical regions, with about 500 genera and 6,000 species worldwide. Coffee is traditionally believed to possess certain medicinal values, such as aiding digestion, refreshing the mind, stopping bleeding, reducing heat, and boosting physical strength. Another well-known member of the Rubiaceae family is gardenia, whose fruit was dried and used as medicine long ago.

The Three Native Species of Coffee

There are about 40 species in the Coffea genus, but only Arabica, Robusta, and Liberica produce coffee beans with commercial value, and they are collectively called the "three native species of coffee."

1. Arabica (scientific name Coffea arabica)

Arabica originated in the Abyssinian Plateau of Ethiopia, which is now the Ethiopian Highlands. In its early days, it was mainly used as medicine; Islamic lovers once regarded it as a secret remedy for regulating body and mind, or used it to refresh themselves. By the 13th century, people gradually developed the habit of roasting and drinking it; in the 16th century, it spread to Europe via the Arabian region, and afterward gradually became a beverage loved worldwide.

Among all coffee, Arabica accounts for about 75% to 80%. Its outstanding flavor and aroma make it the only one of the three native species that can be drunk directly. However, Arabica has relatively weak resistance to drought, frost damage, and pests and diseases, and is especially vulnerable to coffee's natural enemy—leaf rust—so producing countries continue to improve varieties. Sri Lanka is a typical example: it was once a famous coffee-producing country, but at the end of the 19th century, due to the rampant spread of leaf rust, almost no coffee estate was spared. After that, Sri Lanka turned to developing the black tea industry and, together with India, became a black tea kingdom.

The main origins of Arabica coffee beans include South America (except Argentina and parts of Brazil), Central America, Africa (Kenya, Ethiopia, and other mainly East African countries), and Asia (including Yemen, India, and parts of Papua New Guinea).

2. Robusta (scientific name Coffea robusta Linden)

Robusta is a leaf-rust-resistant variety discovered in Congo, Africa, and its disease resistance is stronger than that of Arabica. People are accustomed to discussing Robusta alongside Arabica, but in fact Robusta was originally a mutant variety of Coffea canephora. Strictly speaking, the one that should truly be mentioned alongside Arabica is Coffea canephora. However, today the name Robusta has been widely accepted by the public and is regarded as the same category as Coffea canephora.

Arabica coffee beans are suited to growing in the cooler high-altitude areas of the tropics, while the hot, humid zones unsuitable for Arabica are exactly the growing areas for Robusta coffee. Robusta has a distinctive aroma, commonly called the "Robusta taste" or off-flavor, which some people regard as a musty odor, and it also carries bitterness. It only needs to account for 2% to 3% of a coffee blend for the entire cup to show a Robusta taste. Its flavor is distinct and intense, and if you want to taste it directly, you may need to be mentally prepared. It is usually used in instant coffee (the extracted coffee liquid is about twice that of Arabica), canned coffee, liquid coffee, and other industrial coffee products. The caffeine content of Robusta is about 3.2%, far higher than Arabica's 1.5%.

The main producing countries of Robusta include Indonesia, Vietnam, and West African countries centered on Côte d'Ivoire, Algeria, and Angola. In recent years, Vietnam has become more actively involved in the ranks of major coffee-producing countries and has included coffee production in national policy (Vietnam also produces some Arabica coffee).

3. Liberica (scientific name Coffea liberica)

West Africa is the original home of Liberica coffee. It has strong adaptability to various environments such as high or low temperatures and humidity or dryness, but it is not resistant to leaf rust, and its flavor is also inferior to Arabica. Therefore, it is only traded domestically in some West African countries (Liberia, Côte d'Ivoire, etc.), or cultivated for research use.

About 65% of the coffee circulating in the world market is Arabica

According to statistics from the International Coffee Organization (ICO), excluding domestic trade within coffee-producing countries, about 65% of the coffee circulating in the world market is Arabica and 35% is Robusta. Arabica is characterized by slender, flat beans, while Robusta coffee beans are rounder, making them easy to distinguish by shape alone.

But if hybrids of Arabica and Robusta are also included—for example, the sub-variety Variedad Colombia, which is a main variety of Colombian coffee and has one-quarter Robusta blood, thus resistant to leaf rust and high-yielding—along with their mutated sub-varieties of coffee beans, the classification becomes even more complex. Some Arabica coffee beans are quite close to the native species, while some Arabica beans are quite similar to Robusta. Even if the coffee name is the same (named after the origin), the flavor will differ as long as the cultivated variety is different.

Coffee Cultivation Conditions

There is a term called the "Coffee Belt." There are more than 60 coffee-producing countries in the world, most of which are located in the tropical and subtropical regions between the Tropic of Cancer and the Tropic of Capricorn (23°26′ north and south latitude). This coffee cultivation zone is called the "Coffee Belt" or "Coffee Zone."

The average annual temperature in the Coffee Belt is above 20°C, because the coffee tree is a tropical plant and cannot grow normally if the temperature is below 20°C.

1. Climatic Conditions

Arabica coffee is not tolerant of hot, humid climates, nor can it remain for long periods in low temperatures below 5°C, so it is mostly planted on steep slopes at altitudes of 1,000 to 2,000 meters. On the other hand, because Robusta coffee has strong adaptability (the original meaning of Robusta is "strong and robust"), it is mostly planted in lowlands below 1,000 meters.

Even rainfall throughout the year, with precipitation of 1,000 to 2,000 millimeters, plus moderate sunlight, is the most suitable environment for coffee growth. However, Arabica coffee is not tolerant of strong sunlight and intense heat, so it is suitable for planting in terrain prone to morning fog, especially places with large temperature differences between day and night. In addition, in some places, shade trees such as bananas, corn, and mango trees are planted to avoid direct sunlight.

2. Soil Quality

Simply put, soil suitable for growing coffee is fertile volcanic soil with sufficient moisture and water and rich in organic matter. The Ethiopian Highlands are covered with this kind of weathered volcanic soil, so soil rich in humus naturally becomes one of the basic conditions suitable for growing coffee.

In fact, the Brazilian plateau region (called "Terra rossa," meaning fertile red soil weathered from basalt), the Central American highlands, the areas around the South American Andes, the African highlands, the West Indies, and Java (where the soil in some places is also weathered volcanic soil or a mixture of volcanic ash and humus)—the main coffee-producing regions—also have moist, fertile soil just like the Ethiopian Highlands.

Soil quality has a subtle influence on coffee flavor. For example, coffee grown in more acidic soil will also have stronger acidity; and in the Rio de Janeiro area of Brazil, the soil has an iodine flavor, and when coffee beans are harvested by shaking the tree to drop the fruit to the ground, the coffee also picks up that distinctive taste.

3. Terrain and Altitude

It is generally believed that coffee produced in highlands is of better quality. Because mountain ranges run through the center of the continent in Central American coffee-producing countries, they use "altitude" as a grading standard. For example, Guatemala's SHB (Strictly Hard Bean), the highest of seven grades, is called SHB, indicating that its production altitude is about 1,370 meters.

Although coffee estates located on steep, high slopes are inconvenient in terms of transportation, carrying, and cultivation management, such terrain has low temperatures and is prone to morning fog, which can soften the intense sunlight unique to tropical regions and give the coffee fruit time to fully develop and mature.

However, high-grade coffees such as Jamaica's "Blue Mountain" and "Hawaii Kona" are not highland-harvested coffees. Because as long as there is suitable temperature, rainfall, and soil, morning fog, and large day-night temperature differences, high-quality coffee can be grown. From this we can see that even if "highland production equals high quality," it does not mean "lowland production equals low quality." Altitude can only be regarded as one reference standard for judging coffee grade. Although altitude is important, the terrain and climatic conditions of the origin are even more important.

The main coffee consumer markets, European countries, long ago gave high evaluations to highland coffees such as those from Kenya and Colombia. A fixed amount of coffee beans can extract more coffee liquid (that is, higher concentration), which is also one reason why highland coffee has won praise.

In addition, as mentioned earlier, Robusta coffee, native to Congo, is planted in lowlands below 1,000 meters. Unlike Arabica, it grows quickly and resists pests and diseases, and can be planted even in infertile soil, so its taste and aroma are far inferior to Arabica coffee.

The Coffee Cultivation Process

People often mistakenly think that coffee is planted directly from green beans, and after spending a lot of effort planting them, they find that they simply will not sprout. In fact, coffee must be planted from seeds with the parchment layer still attached. "Parchment" (also called "sheepskin" or "paper skin") refers to the brown hard skin wrapping the coffee seed, and coffee beans with that layer attached are called "Parchment Bean."

If you peel open a fully ripe bright red coffee fruit (called a red cherry), you can see yellow flesh beneath the red skin, somewhat like a cherry. The flesh is sweet, and in the center there is a pair of symmetrical seeds. Around the seeds is a slippery membrane; washing the membrane off with water turns them into "parchment bean." If you remove the parchment, you will see seeds wrapped in silver skin, and those seeds are the green beans actually used as coffee raw material.

1. Sowing

Plant coffee seeds still wrapped in parchment into a seedbed (a plastic flowerpot called a "pot"), and they will sprout in 40 to 60 days. About 6 months after sprouting, they will grow into seedlings about 50 centimeters tall. At this stage, the seedlings are still fragile, and the seedbed must be covered with things such as cold-protection gauze to block direct sunlight.

About three years after the seedlings are transplanted from the seedbed to the plantation, they bloom. During this period, in countries such as those in Central America that use hand-picking to harvest coffee beans, in order to improve coffee harvesting efficiency, the branches of the coffee tree are pruned, removing the lower side branches. The coffee tree's flower is a white five-petaled flower with jasmine fragrance. The flower withers within a few days, then small fruits grow, turning red, which represents maturity, after 6 to 8 months.

The peak coffee harvest period is during the 6 to 10 years after the coffee tree has grown, after which the yield gradually declines. In addition, if the coffee tree grows too tall, it will also cause a poor harvest, so coffee farmers saw off the trunk at 30 to 50 centimeters above the ground to let it regrow branches and renew productivity. This step is called "Cutback." If favorable conditions such as climate, fertilization, and pest and disease resistance are also provided, the coffee tree can continue bearing fruit for 20 years, or even 50 years.

Wild coffee trees can grow to about 10 meters tall, but generally cultivated coffee trees are kept at a height of about 2 meters for ease of harvesting. Arabica coffee varieties are improved year after year, hoping to achieve high yield, strong virus resistance, early harvest period, and strong environmental adaptability, and of course also a suitable tree height to make harvesting more efficient.

2. Harvesting

The coffee harvest period and harvesting methods vary by region. Generally speaking, it is about 1 to 2 times a year (sometimes as many as three or four times). The harvest period is mostly in the dry season. For example, in Brazil it starts around June from Bahia in the northeast and proceeds southward in sequence, ending around October in Parana in the south. In Central American countries, the harvest period is about September to January of the following year, harvesting from lowlands to highlands.

Harvesting methods are broadly divided into two types: hand-picking and stripping.

(1) Hand-picking

Except for Brazil and Ethiopia, most Arabica coffee-producing countries use hand-picking for harvesting. Hand-picking is not only about picking the ripe bright red coffee cherries; sometimes unripe green coffee cherries and branches are picked along with them, so these unripe beans often end up mixed into the refined coffee beans, especially when the natural method is used for processing. If these beans are also mixed in during roasting, they will produce a nauseating odor.

(2) Stripping

This method uses sticks to beat the ripe fruit or shakes the coffee branches to make the fruit fall and gather into piles. Larger estates use large harvesting machines, while small and medium-sized farms use a whole-family human-wave tactic to harvest. This method of shaking the fruit onto the ground makes it easier to mix in impurities and defective beans than hand-picking. In some origins, the beans even pick up peculiar off-flavors, or the beans ferment because the ground is wet. Producing countries of Robusta coffee beans such as Brazil and Ethiopia mostly harvest in this way.

Countries that harvest by stripping also mostly use the natural drying method to process coffee beans. Coffee blooms in spring, bears fruit in summer, and is harvested in winter. Therefore, in places where the distinction between dry and rainy seasons is not obvious, harvesting and drying operations are quite difficult. When the rainy season comes, the natural drying method cannot be used. Therefore, coffee is suitable for growing in regions with distinct dry and rainy seasons.

Coffee Grading

Suppose two café owners are discussing. Owner A says: "The coffee beans we use in our shop are Brazil Santos NO.2. What about your shop?" Owner B says: "Our shop uses Brazil NO.1, the same grade as Blue Mountain NO.1."

Brazil uses an evaluation method called the "demerit system," ranking grades according to how many defective beans are in each 300 grams of main beans. There are seven levels from NO.2 to NO.8, and a demerit score below 4 is classified as NO.2 (NO.8 has a demerit score of 360). Coffee with not a single defective bean could of course be called NO.1, but such cases are extremely rare and cannot maintain a stable supply, so Brazil sets NO.2 as the highest grade rather than NO.1. From this we can see that Owner B is a poser.

Each coffee-producing country has its own grading methods and quality evaluation standards in order to grade the coffee it harvests (there are also countries like Yemen, which produces the famous Mocha Mattari, that have no unified export specifications). If all coffee-producing countries in the world had a common evaluation standard, it would be much more convenient for buyers. Unfortunately, current grading standards are still based on the national conditions of each producing country.

That said, we can still broadly distinguish them according to the following three points.

(1) Grading according to the altitude of the origin

(2) Grading according to screen size (the size of green beans)

(3) Grading according to screen size and defective bean ratio

1. Evaluating Quality by the Altitude of the Origin

As mentioned earlier, coffee produced in highlands is better than that produced in lowlands, so the altitude of the origin is also included as one of the standards for quality evaluation. The higher the altitude, the lower the relative temperature, and the coffee fruit can mature slowly. Fully mature beans in this way have good expansion and are easy to roast. Therefore, coffee-producing countries in Central America almost evaluate coffee bean quality solely by the altitude of the origin.

For example, for Guatemalan coffee, the country's highest-quality coffee is called SHB, the acronym for Strictly Hard Bean, grown at altitudes above 1,350 meters. Mexico is the same: the highest quality SHG (Strictly Hard Grown) is grown in highlands above 1,700 meters. El Salvador's and Honduras's SHG are also grown in highlands above 1,200 meters.

If coffee-growing areas are all flat plateau zones like Brazil, large-scale mechanization can be adopted, but the main coffee-growing areas of Central American countries are all on hillside slopes, making mechanized farming difficult. It is said that Jamaica's Blue Mountain area even has dangerous slopes with inclines exceeding 40 degrees.

Planting in such places means that only hand-picking can be used to carefully pick each ripe red fruit one by one. Although the cost is higher, it can produce high-quality coffee with few impurities and defective beans.

Quality and Grading of Guatemalan Coffee Beans

2. Evaluating Quality by Screen Size

Countries that use screen size to evaluate quality include Kenya, Tanzania, Colombia, and other producing countries of Colombian milds (one of the coffee types traded on the New York futures exchange according to origin). So-called judging quality by screen means evaluating quality according to the size of green beans. For various green beans, the bean size is determined by passing them through perforated iron plate screens.

The unit for screen hole size is 1/64 inch, so screen No.17 means 17/64 inch, that is, green beans can pass through a screen with a hole diameter of 6.75 millimeters. Beans larger than this size cannot pass through the screen, while smaller ones can. Therefore, the larger the screen number, the larger the bean size.

Tanzania's highest-grade coffee beans are large beans called AA, requiring a screen of No.18 (7.14 mm) or above; Kenya's AA also requires large beans using screens with holes of 7.2 mm or above. Colombia has two grades, Supremo and Excelso. Supremo requires a screen of No.17 or above, while Excelso uses screen 14/16 (meaning among beans of screen No.16, 11% of screen No.14 beans are mixed in).

Large beans have richer and more varied flavors than small beans. Different screen sizes do indeed produce differences in the taste of the screened beans.

3. Evaluating Quality by Screen Size and Defective Bean Ratio

Next is Brazil, a major coffee country, which uses a combination of defective bean ratio (demerit system), screen size, and cup testing, giving rise to a third evaluation method. For example, when buying Brazilian coffee beans, you may see the label "Brazil Santos NO.2, Screen 19, Strictly Soft." Its explanation is as follows:

· Brazil — name of the producing country

· Santos — port of export

· NO.2 — a grading method indicating the quantity of mixed-in defective beans. NO.2 is the highest grade, while NO.8 is the lowest limit for export sales specifications.

· Screen 19 — indicates bean size. Brazil uses 12-20, and the larger the number, the larger the bean. 19 indicates beans that pass through a screen with 7.54 mm holes. However, this grading method is only used for flat beans; peaberry must be graded using special oval-hole screens (8-13).

· Strictly Soft — indicates the cup testing grade. Strictly Soft represents the highest grade.

Brazilian-style cup testing grades:

Grade 1: Strictly Soft

Grade 2: Soft

Grade 3: Softish

Grade 4: Hard

Grade 5: Rio (light iodine flavor)

Grade 6: Rioy (strong iodine flavor)

Grades 1-3 here are collectively called "soft." With balanced sweetness, bitterness, and acidity, they are quite mild, good-quality coffee. On the contrary, grades 5 and 6 are inferior products with an iodine odor. The soil around Rio de Janeiro in Brazil has a strong iodine flavor, and when coffee fruit falls onto this soil during harvesting, it picks up that distinctive taste.

Brazil's three-part grading method has not been adopted in other countries, because there is no need. In other words, even without "cup testing," one can know that these coffees have a certain quality. The reason Brazil uses this "cup testing grading method" is that its producing areas are too large and it produces too many beans. In order to blend coffee flavors specifically for export, these coffee beans are often mixed together, resulting in uneven quality that requires "cup testing" for grading.

For this reason, Brazilian coffee graders must comply with strict requirements: in order for taste and smell to function fully when appraising coffee, these graders not only cannot have cavities, but also cannot eat foods that numb the tongue, such as chives, onions, and garlic. Tobacco, alcohol, and strongly scented perfumes are of course also prohibited. At the gates of Zen temples, stone pillars often stand reading "Meat, strong-smelling vegetables, and alcohol are forbidden at this mountain gate." Here "strong-smelling vegetables and alcohol" refers to pungent green vegetables such as chives and scallions, as well as alcohol. Brazilian coffee graders are like Zen monks, mainly eating vegetarian food every day.

In addition to the three grading methods mentioned above, some regions, like Jamaica, use classification by cultivation area.

The grading methods of producing countries are various, and remembering them all requires some skill, but once you are familiar with them, they are no big deal. In short: "Large-bean coffee from highlands with no defective beans is good coffee."

Quality and Grading of Brazilian Coffee Beans (deducting points according to the amount of defective beans and impurities mixed into each 300 g of coffee beans, then classifying the beans into NO.1 to NO.8 according to the deduction)

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