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

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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 bean in the market, primarily grown in the highland regions of the Western Hemisphere, including Brazil, Colombia, and other Latin American countries. Brazil and Colombia are the world's first and second largest coffee-producing countries respectively. Both grow at altitudes exceeding 2,000 feet in regions with moderate and stable temperatures. Arabica coffee trees take five years from seedling planting to bear fruit. The main harvest period in Brazil is from May to September, while in Colombia it's from April to June. Total production accounts for approximately 70% of the global market. The flavor is relatively mild, with fragrance and wine-like acidity, offering higher quality at a relatively higher price.

Arabica coffee beans are smaller in size, with an oblong front face and a narrow, curved S-shaped crack in the middle. The back of the bean has a relatively complete arc shape. Robusta coffee beans are larger in size, with a more circular front face and a straight crack in the middle. (The VivOlé Arabica coffee beans in the image below are Maragogype elephant beans, which are of higher grade and also larger in size)

Volatile Compounds

Volatile compounds are the main source of coffee flavor and are particularly important for coffee quality. Coffee contains numerous types of volatile compounds, and their presence affects the quality of coffee aroma. Their primary source comes from non-volatile compounds in green beans that are broken down or react during the roasting process. Thermal decomposition, other reactions, or interactions between components such as sugars, amino acids, organic acids, and phenolic compounds result in the formation of coffee's unique aroma and flavor. Factors affecting the composition of coffee volatile compounds include: coffee bean variety, cultivation climate, soil conditions, green bean storage, roasting temperature and time, and roasting equipment.

Green coffee beans do not possess coffee's special aroma and are therefore not consumed directly. They must undergo roasting to generate a large amount of volatile aromatic compounds. After roasting, green coffee beans have been analyzed to contain at least 660 types of main volatile aromatic components, making coffee the food with the most types of volatile aromatic components among all foods and beverages. The aromas generated during roasting, such as hazelnut, creamy, and caramel flavors, or grassy, smoky, burnt, spicy, and bitter tastes, mostly come from volatile compounds. Additionally, differences in roasting degree also affect coffee's flavor characteristics.

Pectin and Lignin

Pectin is a substance formed by the combination of various polysaccharides, mainly composed of galacturonic acid polymers, arabinose, and rhamnose, with a content of over 3%. Lignin is the insoluble residue remaining after plant material is treated with sulfuric acid and caustic alkali, also known as coffee fiber, with a content of approximately 2.4%.

Nitrogen-Containing Compounds

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

Alkaloids

Primarily caffeine, which varies significantly in content among different varieties in green coffee beans. Robusta has higher content, averaging about 2.2% of dry weight, while Arabica has less, averaging about 1.2%. In recent years, low-caffeine coffee varieties have been cultivated in Java and Côte d'Ivoire, with caffeine content as low as 0.2%. Caffeine can be removed using various methods to produce various decaffeinated products. Decaffeinated instant coffee powder has caffeine content below 0.3%, with most commercial products controlled between 0.1% and 0.2%. Caffeine can be said to be the spirit of coffee and also the most controversial aspect.

Although caffeine has no peculiar odor, it has a significant bitter taste. Although some have tried to determine caffeine content by the presence or absence of bitterness, this has not been completely successful because caffeine's bitterness accounts for only a small portion of coffee's overall bitterness, so decaffeinated coffee's bitterness is not significantly affected.

After being digested by the human body, caffeine is rapidly absorbed and metabolized and excreted through urine. The increase in caffeine content in human blood depends on the amount in the stomach. The most significant physiological effect of caffeine on the human body is its stimulation of the central nervous system. As for changes in brain activity, the required dose is extremely high, much higher than normal intake levels. Other notable physiological effects include impacts on blood pressure and cardiovascular issues.

Trigonelline

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

The direct impact of trigonelline on coffee quality is minimal. Its bitterness is only one-quarter that of caffeine, and due to its low presence, it doesn't significantly affect taste. The content in green coffee beans varies by variety, with Arabica having higher content than Robusta. Trigonelline decomposes rapidly during roasting, with a loss rate between 50% and 80%, depending on roasting temperature and time. Additionally, trigonelline decomposes to form various compounds, including non-volatile nicotinic acid, and 29 volatile substances, of which 9 have been identified as containing coffee aroma compounds.

Nicotinic Acid

The content of nicotinic acid in green coffee beans is very low, but it increases after roasting, mainly because it results from the decomposition of trigonelline. However, research findings show that under high roasting temperatures, nicotinic acid continues to decompose into volatile chemical substances, so the actual increase is not significant.

Knowledge Extension

Caffeine accounts for 0.9%-1.4% in Arabica varieties: Canephora usually accounts for 2%, sometimes exceeding 3%

In Summary

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