Transcript Chapter 4
Chapter 4 Coffee Objectives At the end of this chapter, student will be able to: • Differentiate the coffee processing method i.e. grading, roasting, blending • Identify the important chemical composition that can be found in coffee • Recognize several coffee products that can be found in Malaysia Coffee history • The coffee tree belongs to the Rubiaceae family, genus Coffea • Although more than 80 coffee species have been identified worldwide, only two are economically important. • Coffea arabica, also known as Arabica coffee, is responsible for approximately 70% of the global coffee market, and Coffea canephora or Robusta coffee (commercial name of one of the main C. canephora cultivars). • Arabica and Robusta coffees are different in many ways, including their ideal growing climates, physical aspects, chemical composition, and characteristics of the brew made with the ground roasted seeds Properties of coffee • Coffee fruits are typically harvested in one of three ways: picking, stripping, or mechanical harvest. • In the first method, the ripe fruits, known as cherries, are picked one at a time. Because coffee fruits do not usually ripen simultaneously, this method is time-consuming and therefore expensive where the size of the workforce is not sufficient. • However, picking tends to produce better-quality coffee seeds, in terms of both taste and health, than other methods. • Mechanical harvesting is performed by shaking the trees or by stripping the branches with an apparatus similar to a flexible comb. • Stripping and mechanical harvesting yield defects derived from fruits in different degrees of maturation and fermented fruits. Dry method • Dry process, also known as unwashed or natural coffee, is the oldest method of processing coffee. Essentially, the goal of the method is to dry the whole cherry, achieved in three steps: cleaning, drying and hulling • The entire cherry after harvest is first cleaned and then placed in the sun to dry on tables or in thin layers on patios • The harvested cherries are usually sorted and cleaned, to separate the unripe, overripe and damaged cherries • This can be done by winnowing, which is commonly done by hand, using a large sieve. • The drying operation is the most important stage of the process, since it affects the final quality of the green coffee. The goal is to get the coffee to its optimum 12.5% moisture level. Wet method • The wet-processing technique is more sophisticated and generally produces a higher quality brew. Before dehulling and separating the seeds, cherry selection takes place in flotation tanks, followed by soaking and fermentation. • During fermentation, during which enzymes may be added, the silver skin is removed and acidity increases; the pH may be reduced to 4.5. • The seeds (parchment coffee) are then extensively washed, polished, and sun-dried and/or air-dried. Wet processing is frequently used where coffee is harvested by picking, such as Colombia, Asia, and Central America. • Then passed through a series of cleaning, screening, sorting and grading processes. Grading • Grade is generally used to indicate coffee bean size, which is associated with coffee quality. • The process of determining coffee bean size, or grading, is done by passing unroasted beans through perforated containers, or sieves • The method of grading coffee (classifying coffee quality) varies by country, and may include bean size, bean density, number of defects, growing altitude, taste Grading and classification is usually based on some of the following criteria: • • • • • • Altitude and/or region Botanical variety Preparation (wet or dry process = washed or natural) Bean size (screen size), sometimes also bean shape and colour Number of defects (imperfections) Roast appearance and cup quality (flavour, characteristics, cleanliness…) • Density of the beans Roasting • At the end of the extensive processing, we are finally left with the green bean which generally has a grassy, earthy aroma • Roasting allows the bean to reach that rich aroma and flavor that we so often associate with coffee • the beans are heated in a big piece of machinery (the roaster) that spins them around at a certain speed (controlled by the person doing the roasting) at a certain temperature (also controlled by a person) for 8-15 minutes • A chemical process takes place inside the bean, where - among other changes - starches are converted into sugars. (caramelization) • beans will be roasted for different lengths of time and at different temperatures, resulting in what we call light, medium or dark roasts. Blending • Blending is definitely the mixing up of various kinds of coffee. • Blending together is completed on most occasions to attain a particular taste. Mixing of coffee bean at various age groups and various level of cooking. This is known as Melange technique. • This process is where mix the level of acidity of young and fresh coffee beans mix with all the dark, much more roasting coffee beans to create a much vibrant flavour. • Different blends serve different needs and tastes. Blending can be done before or after roasting. Blending after roasting has some advantages like flexibility. Can adjust the different blending percentages after roasting. One of the more common practices is to blend dark and light roasts to maximize the complexity of roast taste. • The problem it's more cumbersome and more time consuming. Chemical composition • The nonvolatile fraction of green coffee is composed primarily of water, carbohydrates and fiber, proteins and free amino acids, lipids, minerals, organic acids, chlorogenic acids, trigonelline, and caffeine Structure: • The chemical structure of caffeine is shown here: • Caffeine: 1,3,7-trimethyl-2,6-dioxopurine • Caffeine is a methylxanthine with bitter characteristics; however, it is responsible for no more than 10% of the perceived bitterness of the coffee beverage. This alkaloid is heat stable, and its concentration in C. canephora is approximately twice that found in C. arabica • Trigonelline is an alkaloid biologically derived from enzymatic methylation of nicotinic acid. It contributes to the bitterness of the brew and is a precursor for the formation of different classes of volatile compounds during roasting such as pyrroles and pyridines. The amount of trigonelline in C. canephora is approximately two-thirds that found in C. arabica. Volatile compounds in green coffee • The poor volatile fraction of unroasted coffee seeds gives them a weak but characteristic aroma. • The most abundant classes of volatile compounds are alcohols, esters, hydrocarbons, and aldehydes. Ketones, pyrazines, furans, and sulfur compounds have also been identified. • The volatile composition of coffee berries as with the seeds, the volatile composition of coffee berries is dominated by high levels of alcohols, mainly ethanol, in all stages of ripeness. • Overripe coffee berries, which produce black defective seeds, exhibited high concentrations of volatile compounds dominated by esters, followed by alcohols, ketones, and aldehydes, with very low levels of monoterpenes. After roasting • It is only during roasting that the complex aroma of coffee is formed by pyrolysis, Strecker degradation, and Maillard reaction. The variety and concentrations of volatile compounds in roasted coffee depend on the composition of nonvolatile compounds in the raw seeds and on roasting conditions. Decaffeinated coffee production • Decaffeinated coffee is generally consumed by people with health disorders or those in search of a healthier lifestyle. • This population is characterized by a low rate of smoking, low alcohol consumption, and high consumption of health supplements. • Decaffeination is performed before roasting. The least costly caffeine extraction methods use an organic solvent (dichloromethane or ethyl acetate) and water/vapor before and after extraction to wash the seeds and open the pores. • After caffeine removal, the seeds are dried until they reach moisture content similar to that prior to processing. • The caffeine extracted from the green seeds can be recovered and used for commercial products such as cola beverages and pharmaceutical drugs. Key flavor components can be lost during the decaffeination process especially when using solvents that lack specificity (e.g., water). Instant coffee production • Instant coffee production typically involves treating ground-roast coffee with hot water and high pressure to extract the water-soluble compounds. • This soluble material is then cooled and sometimes centrifuged, concentrated by heating, and dried through freeze-drying to reduce moisture to approximately 5%. • The spray-drying process uses high temperature under high pressure to volatilize the aqueous extract; hot air then dehydrates the small drops, which are powdered. • The freeze-drying process uses very low temperatures to achieve sublimation of the frozen aqueous extract. • Manufacturers use different techniques to improve the appearance and taste of the final product. Although ground-roast coffee generally consists of Arabica species alone or a high percentage of Arabica, Robusta coffee is often used at a high percentage or alone in blends designated for instant coffee production, because Robusta seeds contain higher amounts of soluble solids, which increases yield. Coffee Industry in Malaysia • Coffee in Malaysia was grown mostly by smallholder either monocrops or as inter-crop with coconut • Coffee is a perennial crop with about 66 species but only 3 species was commercially grow. The commercial species was Coffea liberica, Coffea robusta and Coffea arabica. In Malaysia only Liberica and Robusta species was grown. • The Liberica varieties are popular in Johor and Selangor and the Robusta variety planted on Northern Peninsular Malaysia and Sabah and Sarawak. • Total area of coffee growing area was decrease from 9,470 hectare in 1998 to only less than 3,000 hectare in 2009. This occurrence due to the lack of farmers interests to grow coffee because of low income compare and farmers changing coffee area with oil palm crops. • Traditional area such as in Batu Pahat, Muar, Pontian, Sabak Bernam and Bagan Datok Perak mostly converted the vegetation to oil palm.