Coffee is an evergreen shrub or small tree indigenous to central Africa and Asia.Thereare many species of coffee, but three species are of commercial importance:Coffeaarabica,which supplies the largest and best quality of coffee beans,Coffearobusta,(C.canephora) which yields beans of lower quality andCoffealiberica, whose beans are of still lower quality.C.arabicais indigenous to Ethiopia and was introduced to India through Arabia. It is cultivated in South India, mainly in the states of Karnataka, Kerala and Tamil Nadu. It is best grown in the American tropics, where Brazil is by far the largest producer and exporter of Arabica coffee.
Considerable quantities ofC.robustaare also produced in India because the plant can be cultivated at a lower elevation, is longer living and disease resistant, and the yield of coffee bean is greater than fromarabica. Therobustavariety gives thick, strong decoction.C.libericahas not been popular in India as the tea plant is susceptible to diseases and the beans have not foundfavourin the market.
Coffee flowers are white and sweet smelling, producing green berries which turn red when ripe. The berry contains a mucilaginous pulp with two greenish grey seeds or beans, each covered by a thin membrane, the silver skin, and both are enclosed in a common husk-like membrane orparchament. Sometimes a single bean fills the berry instead of two, when the seed is called apeaberry, since it is like a pea. The berries are picked when ripe. Unripe berries give defective beans (Triage) and overripe ones are difficult to beat to a pulp.
Coffee processing consists of removing the skin, pulp, parchment and silver skin.The quality of the final product depends upon the manner of processing.Two methods are employed for processing:
In this method, the berries are sun dried by spreading them out on drying floors and the coverings are removed by hulling. The beans are later cured in curing sheds. The product obtained is known in trade as cherry or native coffee.
1. Dry Method
In the wet method, the ripe fruits are squeezed in a pulping machine which removes the soft outer pulp, leaving a slippery exposed layer of mucilage.The mucilage is removed by spontaneous fermentation. This is sometimes facilitated with added enzymes.The seeds separating from the pulp are washed and subsequently dried to a moisture content of 12 per cent.The wet method gives better quality coffee with a bluish-greencolour(green coffee).The green seeds are then graded and packed.Green coffee may be stored for prolonged periods with no adverse effects.
2. Wet Method
(washed coffee process)
Each variety of coffee has its ownflavourand other characteristics. Generally, marketed coffee is a blend of different varieties of coffee beans.The blends are controlled forflavour, aroma,colourand strength or body of the beverage from the roasted bean.
Raw or green coffee has noflavouror aroma and has an unpleasant taste. For use as a beverage, it is roasted, powdered and brewed and the aqueous extract used as a beverage with or without the addition of milk, sugar and other substances.During roasting many physical and chemical changes occur. The beans swell in size to almost double their original size, the dull-greencolourchanges to brown and the characteristic coffee aroma develops. The beans lose their hard horny structure and become brittle, with the outer surface still smooth and firm.
During roasting, pressure develops in the beans ,and this appears to be necessary for the proper development of coffeeflavour. It is said that pressure holds the initial breakdown products together until the proper stage of roasting is reached, when they react with each other to produce coffeeflavour.Theflavouris due to a mixture of numerous components rather than a definite chemical entity and is apparently produced during roasting. Some moisture is lost during roasting and carbon dioxide is produced in a comparatively large quantity, some of it escaping and some being absorbed within the texture of the roasted bean.
Carbohydrates decompose,caramalizeand, perhaps in combination with other substances, contribute to the aroma of the beverage produced from the roasted beans.Fatty constituents are also affected, volatile fatty acids are driven off and complex fats and waxes are cracked to form simple ones.Proteins may be hydrolyzed and give cleavage products.There is little change in the caffeine content of coffee during roasting.
Theflavourof roasted coffee, to a large extent, depends upon the manner and extent of roasting.Theflavourand aroma of coffee are best. when it is freshly roasted and deteriorate on standing.Coffee exposed to air changes more rapidly than coffee not exposed. The staleness of coffee exposed to air is due to the oxidative changes that take place with certain coffee constituents. This is prevented by the presence of carbon dioxide in roasted coffee. On storage, carbon dioxide is lost and so are theflavourand aroma.
Moisture also has a profound effect on theflavourof coffee. Coffee exposed to moisture loses all itsflavourin a relatively short time.The loss offlavourin vacuum packed coffee or coffee packed under pressure using carbon dioxide is less. Since the loss offlavourand aroma is more in ground coffee than in beans, the roasted beans should be freshly ground to obtain quality coffee. In spite of many investigations, it has not been possible to clearly understand the many complex physical and chemical changes taking place during the roasting of coffee beans.
The constituents of coffee that are important in making a good beverage are theflavoursubstances, the bitter substances, and caffeine which is responsible for the stimulating effect of the drink.Caffeine is present in the coffee bean in both the free and combined states. Its content in the bean varies in different species-C.arabicacontains 1.0-1.2;C.robusta1.5-2.5 andC.liberica1.4-1.6 per cent. There is a variation in the amount of caffeine in the seeds of the same species from different parts of the world., Caffeine, in addition to stimulation, also contributes to the bitterness of the coffee
While caffeine is a stimulant, its excess use causes undesirable effects on mental and physical health. It is as much a health hazard as alcohol and nicotine.Chronic caffeine intoxication results in a number of symptoms (caffeinism) which include sleep disturbance, frequent urination, muscular tension, jitteriness, anxiety, etc.Thus, many people who like the taste of coffee but are afraidotadverse health effects of caffeine use decaffeinated coffee. By chemical methods, most of the caffeine can be removed from green coffee.Decaffeinated coffee retains most of the characteristic aroma of coffee.
Several organic acids are present in the aqueous extract from green coffee beans, the predominant beingchlorogenicacid and the least acetic acid.During roasting, formic and acetic acid contents are increased andchlorogenicand other acids like citric andmalicare partially destroyed.The pH of the coffee brew comes down. Acidity affects coffeeflavour, the more acid tasting the coffee, the better are itsflavourand aroma.Robusta beans produce coffee beverage that is less acid-tasting than thearabica-coffee beverage and is generally less desirable so far as taste is concerned.
As already indicated theflavourof roasted coffee is due to a number of components to which the name "coffeol" has been given.More than 600 volatile compounds have been identified in roasted coffee. Low-boilingsulphurcompounds in coffee are the mainflavourcontributors.Chlorogenicacid contributes to the body and astringency of the coffee beverage, and its decomposition products contribute to the aroma of coffee.The decomposition products of sucrose contribute much to thecolourof the beverage and also to some extent the aroma, bitterness and sourness.Protein decomposition compounds seem to be the major precursors of coffee aroma.
Polyphenolicsubstances (tannins) present in coffee contribute to the bitterness of coffee beverage. They are readily soluble at the boiling temperature of water.There are some other substances also present in coffee, which are extracted on boiling, and contribute to the bitter taste and combine with certain metallic salts to give a metallicflavourto the beverage.
Vacuum coffeeDrip coffeePercolator coffeeSteeped coffeeEspresso coffeeIced coffeeSoluble Coffee: e.g. instant and freeze-dried coffee
Chicory (Cichoriumintybus)is a well-known substitute for coffee, often used blended (up to 50 per cent) with the latter, in liquid coffee extracts. It gives a bitterness to the beverage, which some people find refreshing. The part of the plant used is the root which is chopped, roasted and ground.