GCQRI-Lit Review

Draft Copy FACTORS INFLUENCING CUP QUALITY IN COFFEE Photo Courtesy of SPREAD, Rwanda Prepared for the Global Coffee Quality Research Initiative Brian Howard Global Coffee Quality Research Initiative Review 1 Draft Copy quality on a number of levels. At the ex‐ FACTORS IN- porter or importer level coffee quality is linked to bean size, number of defects, FLUENCING CUP regularity of provisioning, tonnage avail‐ able, and physical characteristics. At the QUALITY IN roaster level coffee quality depends on moisture content, characteristic stability, COFFEE origin, organoleptic (taste and smell) quali‐ ties and biochemical compounds. At the consumer level coffee quality is about taste and lavor, effects on health and alertness, Introduction geographical origin, and environmental and sociological considerations. At every link in the supply chain there is the consid‐ eration of price. In 2004 the International Organization for Standardization (IOS) de‐ ined a standard for green coffee quality which entails defects, moisture content, size, and some chemical compounds of beans as well as standardization of prepa‐ ration of a sample from which to perform cup tasting. According to Bertrand, Arabica coffee production makes up 70% of the world total. Consequently this review will deal mainly with C. Arabica with a few no‐ Photo Courtesy SPREAD Rwanda table exceptions in the sections on genetics Cup quality in coffee is affected by a great and crossbreeding for disease resistance. number of factors; agronomic, genetic and production related. In this review the author seeks to summarize the major ind‐ Agronomy: ings of the research that has been con‐ ducted that is speciically related to cup quality and how it is affected by the envi‐ Soil Nutrition ronment in which the coffee tree is grown, the genetic makeup of the coffee plant itself Coffee can be cultivated on a wide variety and the manner in which coffee is prepared of soil types, provided these are at least 2 for consumption. More than 800 aromatic meters deep, free‐draining loams with a compounds combine to give acidity, body good water retention capacity and a pH of and aroma to a cup of coffee. These three 5‐6, fertile and contain no less than 2% or‐ descriptors will serve as the parameters ganic matter. High quality, acidic Arabica around which cup quality is described in coffees tend to be produced on soils of vol‐ this document. canic origin. The quality of coffee is extensive in its dei‐ Van Der Vossen, 2005 expresses concern nition. Leroy et al, 2006 deines coffee that, “to sustain economically viable yield levels, 1 ton green coffee per hectare (4.5 Global Coffee Quality Research Initiative Review 2 Draft Copy acres) per year, large additional amounts of composted organic matter will have to come from external sources to meet nutri‐ ent requirements, especially nitrogen & po‐ tassium. The majority of small land hold‐ Fertilizer ers will not be able to acquire the neces‐ sary quantities and will be confronted with Organic vs Inorganic Fertilizer declining yields. Organic farming does not necessarily prevent disease or pests below Organic production of coffee is often economically harmful thresholds and the thought preferable due to the strong poten‐ humid conditions of heavily shaded coffee tial of negative environmental impacts may actually stimulate the outbreak of oth‐ from fertilizer leaching into surface waters ers. and groundwater. However, any produc‐ tion crop signiicantly depletes its soils Vaast et al, 1998 found that total uptake of ability to replenish key nutrients and hu‐ nitrate (N03) and ammonium (NH4), key mic matter taken from it in the form of nutrients for plant growth and develop‐ produce. Inorganic fertilizer is often ap‐ ment and the limiting nutrient in Arabica plied at rates approaching 100 to 300 kilo‐ Coffee, at any ratio was higher than that of grams per hectare at signiicant expense to plants fed solely with nitrate or ammonium producers. (Carvajal, 1959) Because of the alone. Anaerobic, lack of oxygen, soil con‐ preference for organically produced pro‐ ditions reduced nitrate and ammonium up‐ duce, especially in the specialty coffee take by 50% and 30% respectively and the market, solutions for such a deicit must be presence of dinitrophenol almost com‐ found and implemented in regionally ap‐ pletely inhibited N uptake in any form. propriate ways. Vaast suggests that these results indicate that Arabica coffee is well adapted to acidic In the shaded Indian coffee terrior of Kar‐ soil conditions and can effectively utilize nataka, India Nagaraj et al., 2006 found the seasonally available forms of inorganic that the addition of inorganic potassium in nitrogen (N). These observations can help the form of muriat of potash and sulphate to optimize coffee nitrogen nutrition by of potash had the effect of increased coffee suggesting agricultural practices that main‐ yields over the period of four years at a tain root systems in the temperature range rate of approximately 15%. The difference that is optimum for both ammonium and between the two treatment methods out‐ nitrate uptake. Vaast found that both ni‐ lined by Nagaraj not being statistically sig‐ trate and ammonium uptake peaked when niicant. It should be noted that the soils in root systems were maintained at 34 de‐ which this coffee were planted were receiv‐ grees Celsius. Below this temperature ing approximately 40 to 60 kg of potassium plant color indicated a loss of vigor. There‐ per hectare per year in leaf fall. The study fore both nitrate and nitrite availability in indicated that no consistent trend could be soi, as well as the coffee trees capacity for observed in the cup evaluation report for uptake through ideal temperature regimes, three years. Cup quality of Arabica coffee can be maximized. Van Der Vossen, 2009 was found to be similar in both MOP and notes that excessive calcium and potassium SOP treated plots but that there was a in soils produce a hard and bitter tasting modest improvement in the cup quality of liquor. robusta coffee in the sulphate potash Global Coffee Quality Research Initiative Review 3 Draft Copy treated plots compared to muriate of pot‐ in 1 to 3 year old plots of C. Arabica and I. ash applications in the second and third oerstediana. In these young plots it was years. It should be noted that there has not found that coffee trees were deriving ap‐ been any evidence of changes occurring in proximately 20% of their nitrogen from the the lavour compounds due to agronomic biological nitrogen ixation occurring via use of sulphur or otherwise. (Krishnamur‐ symbiosis with I. oerstediana. No estimate thy Rao, 1989) Studies conducted in Kenya could be derived for plots between 5 and 7 by (Njoroge and Mwakha, 1985) did not years. It is a reasonable assumption to note any difference in liquor quality of cof‐ make that greater availability and uptake of fee between NPK fertilized plots and con‐ soil nitrogen has a strong positive correla‐ trol treatment over eleven years of re‐ tion to cup quality via plant health and search. bean size. Cup quality differences have been found in studies contrasting organic and inorganic fertilization. In a 2008 study undertaken by Malta, et al. no signiicant differences Environmental Factors were observed on the cup quality among beans from conventional and organic Shade vs Sun plants in the irst year. However in the sec‐ ond year, cup quality of some organic It has been shown that on the most appro‐ treated plants was superior when com‐ priate sites, with intensive management, pared to conventionally treated plants. A self‐shading coffee monocultures can give 2 positive effect on sensorial attributes was and 3 fold increases over more traditional observed using cattle manure, either alone shaded systems. (Beer, 1987) Shade tends or associated with coffee straw and green to reduce photosynthesis, rates of transpi‐ manure. ration, plant metabolism and thus demand on soil nutrients. Due to lower nutrient In Hawaii, Youkhana & Idol, 2009 found needs a crop could potentially be obtained that the addition of mulch from shade tree on more marginal soils with lower fertility. pruning signiicantly offset net nitrogen In areas where regular fertilization cannot and carbon losses from coffee cultivation. be guaranteed it is recommended that Improved carbon and nitrogen sequestra‐ some shading trees be retained as a hedge tion in soil was measured over two years against uncertain future soil inputs. Dr. and it was found that soil bulk density did John Beer of CATIE stresses, “The funda‐ not decline in mulched plots as opposed to mental question, when planning the reno‐ signiicant changes in bulk density for un‐ vation or establishment of a coffee and ca‐ mulched plots. cao plantation is whether the owner has the site, education and resources to main‐ Grossman et al., 2006 found that organic tain the crops without shade. Coffee under production standards are being met while shade will survive setbacks far better than available Nitrogen in soil is supplemented monocultures of the crop.” (Beer, 1987) As by nitrogen ixing shade trees. Biological important as the question “could im‐ Nitrogen Fixation is facilitated through the provements in coffee quality through shade use of leguminous shade trees in the genus be made” in a given location, the question Inga with the most signiicant results found of whether a farmer “should” seek to use Global Coffee Quality Research Initiative Review 4 Draft Copy shade in his plantation becomes equally (6) New crop varieties

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