Coffee Quality Factors


For sheer sensory enjoyment, few everyday experiences can compete with a good cup of coffee. The alluring aroma of steaming hot coffee just brewed from freshly roasted beans can drag sleepers from bed and pedestrians into cafés.

And many millions worldwide would find getting through the day difficult without the jolt of mental clarity imparted by the caffeine in coffee. But underlying this seemingly commonplace beverage is a profound chemical complexity.

Without a deep understanding of how the vagaries of bean production, roasting, and preparation minutely affect the hundreds of compounds that define coffee’s flavor, aroma, and body, a quality cup would be an infrequent and random occurrence.

Yemen’s coffee is distinctive. In a world of increasing homogenization and commoditization, it stands out as a potent relic of uniqueness. This is at once both the source of its difficulties and the source of its success.

Yemen is one of the most historic coffee-producing nations, having launched the trade of what has become one of the world’s most important agricultural commodities distinctive flavors. Some of Yemen’s coffees are prized around the world and receive among the highest prices in the marketplace.

According to the current context of overproduction and low prices of the coffee market, improvement and valorization of coffee quality could provide the coffee chain with a new impetus. In this context, the efficiency of integration of coffee quality as the main target in breeding programs as opposed to its previous status as a secondary selection criterion (Van der Vossen, 2001), will be based on our ability to answer several questions:

i) What is quality?

ii) What are the factors that affect quality?

iii) What strategies have been used up to now to improve and/or maintain coffee quality and what types of results were obtained?

Quality is a trait difficult to define. According to any dictionary, it is an “inherent or distinguishing characteristic”. The International Organization for Standardization (ISO) describes quality as “the ability of a set of inherent characteristics of a product, system or process to fulfill the requirement of customers and other interested parties” (ISO, 2000). These inherent characteristics can be called “attributes”.

For coffee, the definition of quality and the attributes considered have probably evolved over the centuries. Nowadays, this definition varies along the production-consumer chain:

– At the farmer level: coffee quality is a combination of production level, price, and easiness of culture;

– At the exporter or importer level: coffee quality is linked to bean size, lack of defects, the regularity of provisioning, tonnage available, physical characteristics and price;

– At the roaster level: coffee quality depends on moisture content, the stability of the characteristics, origin, price, biochemical compounds and organoleptic quality. It should be noted that each consumer market or country may define its own organoleptic qualities;

– At the consumer level: coffee quality deals with price, taste, and flavor, effects on health and alertness, geographical origin, environmental and sociological aspects (organic coffee, fair trade, etc).

Factors that affect quality :

  • Harvest and post-harvest effects on quality

It is widely agreed that traditional hand-picking and husbandry labor, as opposed to mechanical harvest, produce the best quality green coffee by decreasing the percentage of defects in coffee batches. Then, depending on the postharvest process, strong consequences on coffee quality can be observed. For instance, dry processing is generally avoided for quality samples as it enhances bitterness in the liquor (Barel and Jacquet, 1994).

  • Pedo-climatic effect on the quality

Climate, altitude, and shade play an important role through temperature, availability of light and water during the ripening period. Rainfall and sunshine distributions have a strong influence on flowering, bean expansion, and ripening. For instance, chlorogenic acids and fat content have been found to increase with elevation in C. arabica. The role of soil types has been well studied. It is generally admitted that the most acidic coffees are grown on rich volcanic soils (Harding et al., 1987).

  • Physiology effect on the quality

Tree physiology, plant age, and period of picking all interact to produce the final characteristics of the product. Indeed it was found that tree age, location of the fruits within the tree, and fruits-to-leaves ratio had a strong influence on the chemical content of green beans (Bertrand, 2002; Vaast et al., 2006).

An important attribute of coffee brew or infusion quality is the perceived acidity  (Woodman  1985;  Degenhardt et al., 2006a).    Aliphatic carboxylic acids are the main acids found in coffee and coffee infusions.  Acidity in the strict sense is determined by the hydrogen ion concentration (pH),  which is related to the degree of ionization of a given acid present in aqueous solution.  Changes in pH can, therefore, lead to changes in the character of the flavor as well as the acidity.  Coffee beans may require more days to dry depending on the method of drying and the density at which the beans are dried.

However, information on the effect of drying method and density of drying on the perceived acidity of the green bean  (Coffea canephora var robusta)  and other indicators like crude protein and caffeine in  Ghana is limited.

Acid house

Coffee contains a tremendous number of chemicals, with over 1000  aroma compounds. If you are looking for antioxidants, the most abundant phenolic compounds in coffee are chlorogenic acids (CGAs), which account for up to 12 percent of the dry weight of green unroasted coffee beans. Much of coffee’s bitter taste comes from CGAs, which also cause the acid reflux that is sometimes experienced by coffee drinkers.

Smelling Coffee

aroma science is highly complex. Researchers typically analyze the fragrances evolved during coffee bean roasting by gas chromatography coupled with olfactometry, in which skilled testers sniff and define the smell of each recognizable element. Mass spectrometry is frequently then applied to identify the chemical composition of each odor. Sniffing roasted coffee aromas that have been fractionated by a gas chromatograph is an enlightening experience: one may recognize the aromas of roses, Darjeeling tea, chocolate, vanilla, and violets, as well as truffles, soup, cheese, sweat and even what is called cat scent, which, if diluted, smells like sauvignon blanc wine but in a concentrated sample is disgusting.

In the laboratories of illycaffè, technicians focus on the strongest odorants. Imagine listening to a recording of a choir of 800 singers that includes the strong solo voices of Jessye Norman, Luciano Pavarotti and several other virtuosi who tend to dominate the ensemble. If the volume of the playback is reduced, the stronger voices will still be recognizable even as the choir’s sound fades away. Diluting the aroma of coffee is analogous; beyond a certain point, only the strongest compounds are perceived. Unfortunately, the most powerful molecules in the smell of a coffee sample are those originating from defective beans.

Elemental Coffee Analysis

To guarantee stated quality and safety of a final coffee product and protect the well-being and health of consumers, different parameters responsible for the wholesomeness of green beans, roasted beans, prepared coffee, and its infusions have to be measured using suitable analytical methods. For example, in the organoleptic analysis of green coffee beans, their odor and taste in addition to the information about their size, shape, color, and cross-section are ascertained as a part of the quality assessment (Belitz et al.2009).

Color and flavor characteristics are important to find the best degree of roasting green beans (Belitz et al.2009). For the evaluation of the quality of coffee infusions, the flavor of prepared beverages is commonly described under standardized conditions (Sanz et al.2002). All individual notes of each sample are collected and its unique profile is assessed, however, it should be noted that opinions of qualified coffee testers on coffee taste and aroma can be subjective (Krivan et al.1993; Anderson and Smith 2002).

Chemical methods of coffee analysis are similar to those used in food quality control and assessment (Martin et al. 1998a). They are based on the determination of different compounds, e.g., volatile compounds, caffeine, tannins and polyphenols, lipids, individual carbohydrates like sucrose, glucose, fructose, arabinose, galactose, polysaccharides like cellulose, amino acids, vitamins B3 and PP, chlorogenic acid, trigonelline, and minerals (Bernal et al. 1996; Costa Freitas and Mosca 1999; Anderson and Smith2002; Villarreal et al.2009; Hecimovic et al.2011; Wei et al. 2011).

 These chemical species are often measured for the purpose of discriminating coffee varieties and brands or determining the coffee origin (Bernal et al.1996; Costa Freitas and Mosca1999; Anderson and Smith2002; Villarreal et al.2009; Hecimovic et al. 2011). However, it should be considered that all stages involved in the production of coffee, from coffee harvesting to roasting, can change the composition of the final product (Anderson and Smith2002; Mussatto et al. 2011). Among different substances present in coffee, only caffeine is stable to the excessive roasting temperature (Mussatto et al. 2011).

Other chemical compounds are susceptible to degradation during production and storage conditions (Anderson and Smith2002). Hence, a reliable and independent method enabling to differentiate the geographic growing origin of coffee has to be focused on compounds that are stable during all coffee production stages and subsequent storage. Elements and their concentrations fulfill this requirement and for that reason, the elemental analysis of coffee, aimed at determining its elemental composition, is so important for the purpose of its quality control and bromatological value evaluation (Krivan et al.1993; Anderson and Smith 2002).

Author: Helmi Al-Qadasi – Coffee Quality expert at Mocha Valley.


  • Chemistry in every cup
  • Ernesto Illy the complexity of coffee
  • Pawel Pohl&Ewelina Stelmach&Maja Welna& Anna Szymczycha-Madeja, Determination of the Elemental Composition of Coffee, Using Instrumental Methods
  • Samuel Tetteh Lower*, Franklin Manu Amoah and Kwabena Opoku-Ameyaw Drying process and Ghanaian green coffee quality crude protein, pH and caffeine levels

Cocoa Research Institute of Ghana, P. O. Box 8, Akim Tafo. Ghana.

Accepted 10 November 2007

  • Thierry Leroy1*, Fabienne Ribeyre1, Benóit Bertrand1, Pierre Charmetant1,4, Magali Dufour1, Christophe Montagnon 1, Pierre Marraccini1,2 and David Pot1,3. Genetics of coffee quality



Tags: No tags

Add a Comment

Your email address will not be published. Required fields are marked *