Introduction KOPI!

Coffee is one of the most popular beverages in the world. Nearly 25 million farmers in 50 countries around the world depend on coffee for a significant part of their livelihoods (Cague et al. 2009). Coffee is the most traded commodity second after oil (Ponte 2002). Among coffee drinkers, the average consumption in the United States is 3.2 cups of coffee per day versus 2.6 cups in Canada (Canada 2003).

A good quality cup of coffee is depended on many factors, such as the quality of green beans, the roasting conditions, the time since the beans are roasted, and the type of water used for brewing. More than 800 volatile compounds have been identified in roasted coffee, where of around 30 compounds are responsible for the main impression of coffee aroma (Baggenstoss et al. 2008).

The overall quality and chemical composition of green coffee beans are affected by many factors, such as the composition of the soil and its fertilization, the altitude and weather of the plantation, the cultivation, and the drying methods used for the beans. Coffee plants are mainly grown in tropical and subtropical regions of central and South America, Africa and South East Asia, in temperate and humid climates at altitudes between 600 and 2500 m (Schenker 2000). The genus coffee belongs to the botanical family of Rubiaceae and comprises more than 90 different species (Davis 2001). However, only C. arabica, C. canephora, and C. liberica are of commercial importance (Schenker 2000). As a result of modem breeding techniques some hybrids of C. arabica and C. canephora have recently been introduced with success. Usually roasted coffee beans from different origins are blended at specific ratios to provide coffee of unique flavour profiles. Often time, coffee beans are blended for the purpose of cost saving.

Coffee cherries are harvested each year when they are bright-red, glossy, and firm. After removing the outer hull, the seeds inside of the cherry are commonly called "green coffee beans". The quality of the green coffee beans is dictated by a number of parameters, including bean size, color, shape, method of drying, crop year, and presence of defects (crack, withered bean, bean in parchment, mouldy bean, etc.).

The unique aroma profiles of coffee are closely related to the time-temperature profile used during roasting. The roasting profiles are chosen to produce high quality coffee which are unique to specific brands and must be strictly controlled to meet consumers’ expectations. Coffee producers rely on sensory and physicochemical characteristic evaluations to assure that roasting takes place at the target process parameters. Industrial scale roasting of coffee beans is mainly achieved by conventional drum roasting, in which beans are heated with hot gas in a horizontal drum, or vertical drums equipped with paddles. Roasting time can range from 3 to 12 min, depending on the temperature used, which is typically between 230 to 250oC. By contrast, fluidized bed roasting is achieved by directing high velocity hot air towards the beans, usually from the bottom of the roaster, to suspend the beans in turbulent air. The hot air temperature ranges from 230 to 360oC (Eggers & Pietsch 2001). The roast temperature determines both flavour formation and structural product properties. Different temperature profiles affect dehydration and the chemical reaction conditions in the bean which control gas formation, browning and flavour development. In general, the use of roasting temperature of greater than 200°C is required in order to result in desirable chemical, physical, structural, and sensorial changes in the coffee beans (Clarke & Macrae 1988; Schenker 2000; Schenker et al. 2002; Baggenstoss et al. 2008). Color change and weight loss are frequently used as a measure of the degree of roast, and both are directly related to the final roasting temperature (Sivetz 1991; Illy & Viani 1995). Other methods, such as the ratios of free amino acids (Nehring & Maier 1992), and chlorogenic acids content (Illy & Viani 1995) have also been used.

Researchers have reported the effects of time-temperature profile on coffee aroma properties. In general, low-temperature-long time roast processes result in sour, grassy, woody, and underdeveloped flavour properties. In comparison, high-temperature-short-time produced the higher quality coffee in terms of producing more aroma volatiles and higher brew yield (Schenker et al. 2002; Lyman et al. 2003). Reviewing these and other literature, one can conclude that the complex changes in coffee during roasting do not solely depend on physical parameters at the start and end point of the thermal process, but rather a path-dependent phenomenon. Therefore, to gain insight into the changes of physicochemical properties of coffee during roasting, the green beans must be roasted under controlled conditions.

Source :

Physicochemical Changes of Coffee Beans During Roasting

JAVA PREANGER COFFEE ADDICT

Fadillah Satria

FTIP TMIP UNPAD

fadilprojectkopi@gmail.com