**1. Introduction**

#### **1.1 Arabica coffee production in Kenya**

Coffee is an export oriented crop that contributes significantly to the economic growth of 80 developing countries of the world. Approximately, 125 million people in 50 developing countries of Africa, Latin America and Asia produce and sell coffee as their main source of income [1]. *Coffea canephora* Pierre ex A. Froehner or Robusta coffee, makes 30% of the world's commercial coffee and 80% of the production in Africa, with Uganda being among one of the top most producers [2]. Globally, coffee fetches more than \$ 79 billion US dollars in the world markets [3] and in Ethiopia, when the genetic value of resistance to diseases, pests, high yield and low caffeine is considered, that value rises to between US \$420 - \$1.45 billion [2]. Arabica coffee constitutes 70% whereas Robusta, contributes 30% of the total world product and export [2].

Arabica coffee or *Coffea arabica*, earns Kenya, US\$230 million, and is the most important export commodity after horticulture, tourism and tea. Kenya has some of the best quality Arabica coffees globally, but the production has declined from 130,000 metric tons in 1988 to about 45 metric tons, at present [4].

Being a tropical crop, *Coffea* requires specific environmental conditions for commercial cultivation. The quality of developing bean from flowering to ripening is influenced by altitude, latitude, temperature, rainfall, soil, sunlight, wind and humidity [5–7]. Arabica coffee grows at altitude ranges of 1200–1800 meters above sea level (masl) rainfall amounts range between 400 and 600 mm per season though it is also cultivated at 400 m above sea level as long as there is no frost. Robusta coffee cultivation on the other hand is mostly grown at lower altitudes, between sea-level till to an altitude that limits its vegetative growth.

Compared to Arabica, Robusta coffee has smaller bean sizes, poor flavour and high bitterness content but is tolerant to coffee leaf rust disease, has resistance to white stem borer but is susceptible to drought stress [8, 9]. Due its poorer quality characteristics, Robusta coffee global market value is lower than that of *C. Arabica*.

#### **1.2 Coffee origin and diversity**

The genus *Coffea* L has over 105 species, prevalently found in Africa and Madagascar [9, 10]. *Coff*ea belongs to the genus of the Rubiaceae family, is indigenous to Africa and is widely distributed in the tropics [11]. The centres of origin of Arabica coffee are the mountainous rain forests of Ethiopia, the western and eastern slopes of the Great Rift Valley and the Boma plateau of the Sudan. Wild species of *C. canephor* are found in Guinea, Uganda, Sudan, Northern Cameroon Southern Angola and in the Congo forests [11–13]. *Coffea liberica* Bull. Ex. Hiern, known for its resistance to diseases, insect pests, adaption to low elevation, is native to the tropical forests of Liberia and Cote de Ivoire [14] whereas *Coffea mascara* characterized by low levels absence of caffeine is found in the forests of Madagascar Mauritius and Reunion [11–13].

The diverse existence of the genus *Coffea* in Uganda, with species such as *C. eugenioides* S. Moore, *C. excelsa* Chev and *C. spathicalyx* K. Schum., suggests that the country is the centre of origin [11, 13]. Whereas three of the genus *Coffea* species are economically important, coffee production and its industry depend on two species only; Arabica and Robusta coffee [15, 16]. The third important species of coffee, *Coffea liberica* is produced mainly in Liberia, Java, Malaysia and the Philippines but because of its low yield and poorer quality, it is used only for local consumption. With advanced breeding techniques, commercial interspecific hybrids such as Arabusta (*C. arabica* x *C. canephora*) have been developed. Blending coffees from the two species at varying ratios probably produces the preferred consumer flavours at lower costs [17]. With the exception of *C. arabica* that is tetraploid and self-fertile (2n = 4x = 44), all the other species in the genus *Coffea* are diploid (2n = 2x = 22), with gametophytic self incompatibility and therefore there exists gene flow between them and the cultivated *C. canephora* [18]. Given its allopolyploidy and self-pollinating nature, *C. arabica* is characterized by low genetic diversity leading to a narrow genetic base [1].

#### **1.3 Objectives in coffee improvement programs**

Since the quality of coffee is the key determinant of prices in the world markets, genetic improvement of Robusta coffee organoleptic cup characteristics, yield and caffeine is being undertaken by many researchers throughout the world in an attempt to match Arabica coffee characteristics in order to stabilize and sustain development in the coffee growing areas [17]. Promoting coffee liquor quality would add value, enhance income and increase the competitiveness of the world coffee prices. To sustain value, most coffee improvement programs are aiming to select and breed for cultivars with genetically superior organoleptic cup quality and

**51**

*Organoleptic, Sensory and Biochemical Traits of Arabica Coffee and Their Arabusta Hybrids*

is given priority and is determined alongside genetic traits [19, 20].

are using modern, molecular marker tools such as SSRs, SNPS in combination with, physiological and biochemical green bean tools [17]. In the same manner, the influence of environmental factors such as soil texture, nutrient element composition, altitude, rainfall, temperature that directly or indirectly contribute to coffee quality

Coffee quality is influenced by factors such as the genetics, handling procedures, ecological conditions and agricultural practices. According to the

International Organization for Standardization (ISO) quality is "the ability of a set of inherent characteristics of a product, system or process to fulfill requirement of customers and other interested parties" [21]. Depending on the actors in the value chain coffee quality could refer to, the variety, price of coffee, the consuming culture, tonnage or on bean physical characters and biochemical compounds in the green bean. It is the effect of cup quality that determine commercial coffee grade

Coffee bean physical appearance is an integral indicator of cup quality, but it is the assessment by consumers through their human sensory organs and consumption habits that determine the final quality [17]. The most important attributes are; fragrance, aroma, flavour, bitterness, sweetness, saltness, acidity, mouth feel, aftertaste and cup balance. Fragrance originates from the smell of roasted or ground beans whereas aroma emanates during brewing with boiled water. Aroma helps evaluate flavour and coffee liquor brightness [22]. Flavour is described as an individual person feeling of appreciation during the tasting of the coffee brew taste, which does also include aroma. Fat stabilizes flavour compounds formed during roasting [18, 22, 23]. The undesirable coffee bitter taste in the mouth is positively correlated with the total dissolved coffee solids. High levels of saltiness and undesirable aroma are associated with high levels of potassium in Robusta coffee. Coffee brew taste is less preferred by consumers when potassium and caffeine are at lower levels [24]. Coffee medium roast has less soluble solids, a higher acid content, and more stringent aroma compared to the dark roast [25]. Roasted beans that are less

Acidity is regarded as the sharp and pleasing sweet to fruity/citrus taste close to the dry taste experienced on the back sides of the tongue while drinking red wine. Perceived acidity in coffee does not necessarily correlate with coffee pH, but is a result of the acids such as aliphatic, chlorogenic, alicyclic carboxylic and phenolic acids that are developed during medium and dark roasted stages. Cup acidity is influenced by high concentrations of citric acid, malic acid, and acetic acid and low concentrations of phosphorus and potassium. Acidity is thought to be influenced by phosphoric acid levels,though it may not directly correlate with perceived acidity [26]. Mouth-feel or liquor body is determined by micro fine fiber and fat content. Liquor weight is caused by micro fine fiber particles whereas texture is derived from oils extracted from ground coffee suspended in the brew. Brew colloids are formed when oils coagulate around fibers suspended in the brew. Coffee weight and texture (slipperiness) in the tongue is compared to pure water and is determined by the micro fine fiber and fat content [27]. Viscosity is caused by proteins and fibers in the brew and is normally denser in medium roasted and dark coffees than in lighter

bitter but have a high sweet taste is rated high by many consumers.

roasted beans (http://www.coffeeresearch.org/science/news.htm) [24].

*DOI: http://dx.doi.org/10.5772/intechopen.95520*

**2. Factors that influence coffee quality**

and not the bean size.

**2.1 Organoleptic cup quality**

*Organoleptic, Sensory and Biochemical Traits of Arabica Coffee and Their Arabusta Hybrids DOI: http://dx.doi.org/10.5772/intechopen.95520*

are using modern, molecular marker tools such as SSRs, SNPS in combination with, physiological and biochemical green bean tools [17]. In the same manner, the influence of environmental factors such as soil texture, nutrient element composition, altitude, rainfall, temperature that directly or indirectly contribute to coffee quality is given priority and is determined alongside genetic traits [19, 20].
