Coffee (Coffea)

 Coffee is an evergreen shrub or small tree indigenous to central Africa and Asia.  There are many species of coffee, but three species are of commercial importance: I. Coffea arabica, which supplies the largest and best quality of coffee beans, II. Coffea robusta, (C. canephora) which yields beans of lower quality and Coffea liberica, whose beans are of still lower quality. III. C. arabica is 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 of C. robusta are 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 from arabica. The robusta variety gives thick, strong decoction. C. liberica has not been popular in India as the tea plant is susceptible to diseases and the beans have not found favour in 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 or parchament. Sometimes a single bean fills the berry instead of two, when the seed is called a peaberry, 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.

Processing  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-green colour (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 own flavour and other characteristics. Generally, marketed coffee is a blend of different varieties of coffee beans. The blends are controlled for flavour, aroma, colour and strength or body of the beverage from the roasted bean.

Roasting Raw or green coffee has no flavour or 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- green colour changes 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 coffee flavour. 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 coffee flavour.  The flavour is 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, caramalize and, 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.

 The flavour of roasted coffee, to a large extent, depends upon the manner and extent of roasting.  The flavour and 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 the flavour and aroma.

 Moisture also has a profound effect on the flavour of coffee. Coffee exposed to moisture loses all its flavour in a relatively short time.  The loss of flavour in vacuum packed coffee or coffee packed under pressure using carbon dioxide is less. Since the loss of flavour and 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.

Chemical Composition of Coffee The constituents of coffee that are important in making a good beverage are the flavour substances, 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. arabica contains ; C. robusta and C. liberica 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 afraid ot adverse 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 being chlorogenic acid and the least acetic acid. During roasting, formic and acetic acid contents are increased and chlorogenic and other acids like citric and malic are partially destroyed. The pH of the coffee brew comes down. Acidity affects coffee flavour, the more acid tasting the coffee, the better are its flavour and aroma. Robusta beans produce coffee beverage that is less acid-tasting than the arabica-coffee beverage and is generally less desirable so far as taste is concerned.

As already indicated the flavour of 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-boiling sulphur compounds in coffee are the main flavour contributors. Chlorogenic acid 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 the colour of the beverage and also to some extent the aroma, bitterness and sourness. Protein decomposi­tion compounds seem to be the major precursors of coffee aroma.

Polyphenolic substances (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 metallic flavour to the beverage.

Coffee Making  Vacuum coffee  Drip coffee  Percolator coffee  Steeped coffee  Espresso coffee  Iced coffee  Soluble Coffee: e.g. instant and freeze-dried coffee

Chicory (Cichorium intybus)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.