Introduction to Arabica Coffee Bean Origin Characteristics and the Substances Behind Coffee's Aroma

FrontStreet Coffee - Introduction to Arabica Varieties and Aromatic Components

Types of Coffee

Coffee beans can be broadly divided into three main categories: (1) Arabica coffee trees, (2) Robusta coffee trees, and (3) Liberica coffee trees.

Arabica is the most popular coffee on the market, grown primarily in the highland regions of the Western Hemisphere — Brazil, Colombia, and other Latin American countries among them. Brazil and Colombia are the world's first- and second-largest coffee producers respectively, both growing at altitudes above 2,000 feet in regions with moderate, stable temperatures. Arabica trees take five years from planting to first fruit. Brazil's main harvest runs from May to September, Colombia's from April to June. Arabica accounts for roughly 70% of the global market. Its flavor is relatively mild, with fragrance and wine-like acidity — higher quality, at a correspondingly higher price.

Arabica beans are smaller, with an oblong face and a narrow, curved S-shaped crease down the middle; the back of the bean forms a relatively complete arc. Robusta beans are larger and rounder in front view, with a straight crease. (The VivOlé Arabica beans pictured below are Maragogype elephant beans — a higher grade, and also larger.)

Volatile Compounds

Volatile compounds are the main source of coffee's flavor and are critical to quality. Coffee contains a vast array of them, and their presence shapes the quality of its aroma. They originate largely from non-volatile compounds in green beans that are broken down or transformed during roasting: thermal decomposition and reactions between components such as sugars, amino acids, organic acids, and phenolic compounds generate coffee's unique aromas and flavors. The factors that influence volatile composition include variety, growing climate, soil conditions, green bean storage, roasting temperature and time, and roasting equipment.

Green coffee has none of coffee's characteristic aroma and is never consumed as-is; roasting is what generates its wealth of volatile aromatics. Roasted coffee has been shown to contain at least 660 major volatile aromatic components — more than any other food or beverage. The hazelnut, creamy, and caramel notes generated during roasting, as well as grassy, smoky, burnt, spicy, and bitter impressions, come mostly from these volatile compounds. Roast degree itself also shifts the coffee's flavor profile.

Pectin and Lignin

Pectin is a substance formed from various polysaccharides, mainly galacturonic acid polymers along with arabinose and rhamnose, and accounts for over 3% of the bean. Lignin is the insoluble residue left after plant material is treated with sulfuric acid and caustic alkali — also known as coffee fiber — and makes up roughly 2.4%.

Nitrogen-Containing Compounds

The nitrogen-containing compounds in green coffee can be grouped into alkaloids, trigonelline, nicotinic acid, proteins, and free amino acids, described below:

Alkaloids

The principal alkaloid is caffeine, whose content varies considerably between varieties. Robusta carries more — about 2.2% of dry weight on average — while Arabica averages about 1.2%. In recent years, low-caffeine varieties have been bred in Java and Côte d'Ivoire, with caffeine as low as 0.2%. Caffeine can also be removed by various methods to produce decaffeinated products; decaffeinated instant coffee contains less than 0.3%, with most commercial products controlled between 0.1% and 0.2%. Caffeine might be called the spirit of coffee — and also its most controversial aspect.

Although caffeine has no peculiar odor, it is distinctly bitter. Some have tried to gauge caffeine content from bitterness alone, without success: caffeine's bitterness is only a small share of coffee's overall bitterness, so decaffeinated coffee's taste is not significantly affected.

Once ingested, caffeine is rapidly absorbed, metabolized, and excreted in urine; how much enters the bloodstream depends on the amount in the stomach. Its most significant physiological effect is stimulation of the central nervous system. Changes in brain activity require extremely high doses — far above normal intake — while other notable effects involve blood pressure and the cardiovascular system.

Trigonelline

Trigonelline is a hygroscopic, colorless crystal that is highly soluble in water. It has mild physiological effects, mainly on the central nervous system, bile secretion, and intestinal peristalsis.

Its direct impact on coffee quality is minimal: its bitterness is only one-quarter that of caffeine, and its low concentration barely registers on the palate. Content varies by variety, with Arabica holding more than Robusta. Trigonelline decomposes rapidly during roasting, losing between 50% and 80% depending on roasting temperature and time. The decomposition yields various compounds, including non-volatile nicotinic acid and 29 volatile substances, 9 of which have been identified as coffee aroma compounds.

Nicotinic Acid

Nicotinic acid is present in green coffee only in trace amounts but increases after roasting, mainly because it is a decomposition product of trigonelline. However, research shows that under high roasting temperatures it continues to break down into volatile substances, so the net increase is not significant.

Knowledge Extension

Caffeine accounts for 0.9%-1.4% in Arabica varieties, while Canephora usually sits around 2%, sometimes exceeding 3%.

In Summary

FrontStreet Coffee is a coffee research center that enjoys sharing coffee knowledge with everyone. We share without reservation because we want more friends to fall in love with coffee. We also hold three discounted coffee events every month, because FrontStreet Coffee wants to offer the best coffee at the lowest prices to more friends. That has been our principle for 6 years!

FrontStreet Coffee Recommendation

Since this article touches on Brazil — the world's largest coffee producer — two FrontStreet Brazilian single origins are well worth trying. As the biggest coffee-growing nation, Brazil produces an enormous range of coffees with moderate acidity and a beautifully balanced sweetness, bitterness, and body that suit medium roasting perfectly: fragrant with nuts, mellow on the palate, and at home in both single-origin and blends.

FrontStreet Coffee Brazil Cerrado Red Bourbon (Pulped Natural): A classic Brazilian single origin from Cerrado, a region famous for high-quality beans. This Red Bourbon is roasted medium to release rich aromas of creamed peanut, toasted bread, caramel, and hazelnut, with a round, non-acidic mouthfeel and just a trace of pleasant bitterness. It works as a pour-over but also shines through a moka pot, as an espresso SOE, or in a siphon or French press.

FrontStreet Coffee Brazil Fazenda Rainha (Queen Estate) Yellow Bourbon: From the Mogiana region near southern Minas, where fertile red volcanic soil feeds the cherries and builds remarkably full aromatics. Yellow Bourbon — a natural mutation of Red Bourbon — offers an even cleaner fruit character, and through pour-over, moka pot, or home espresso machine you'll find a sugarcane sweetness found in no other origin, alongside fruity and chocolate notes. Brazil's low acidity and balance also explain why its beans anchor so many of FrontStreet's espresso blends, adding chocolate and cream aromatics while keeping extraction stable.