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There are two main species of the coffee plant; Arabica is the traditional coffee, and considered superior in flavor. Robusta, which is higher in caffeine, can be cultivated in environments where Arabica will not thrive, leading to its use as an inexpensive substitute for Arabica in many commercial coffee products. Robusta is not usually consumed by itself, due to its bitter and acidic flavor. Higher quality Robustas are used as ingredients in some espresso blends.
Arabica coffees were traditionally named by the port they were exported from, the two oldest being Mocha and Java. The modern coffee trade is much more specific about origin, labeling coffees by country, region, and sometimes even the producing estate. Coffee aficionados may even distinguish auctioned coffees by lot number.
One unusual and very expensive variety of robusta is the Indonesian Kopi Luwak. The beans are collected from the droppings of the Common Palm Civet, whose digestive processes give it a distinctive flavour.
Although not well-known, certain types of coffee are known to improve with age; they obtain a less acidic, more well-balanced flavor. Several coffee producers sell coffee beans that have been aged to 3 years, and there are several specialty stores (such as Toko Aroma in Bandung, Indonesia) which age their unroasted beans to 8 years.
The roasting process is integral to producing a savory cup of coffee. When roasted, the green coffee bean expands to nearly double its original size, changing in color and density. As the bean absorbs heat, the color shifts to yellow and then to a light "cinnamon" brown. During roasting oils appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source.
At lighter roasts, the bean will exhibit more of its "origin flavor" - the flavors created in the bean by the soil and weather conditions in the location where it was grown. Coffee beans from famous regions like Java and Kenya are usually roasted lightly so their signature characteristics dominate the flavor.
As the beans darken to a deep brown, the origin flavors of the bean are eclipsed by the flavors created by the roasting process itself. At darker roasts, the "roast flavor" is so dominant that it can be difficult to distinguish the origin of the beans used in the roast. These roasts are sold by the degree of roast, ranging from "Light Cinnamon Roast" through "Vienna Roast" to "French Roast" and beyond.
In the 19th century coffee was usually bought in the form of green beans and roasted in a frying pan. This form of roasting requires much skill to do well, and fell out of favor when vacuum sealing of pre-roasted coffee became possible. Unfortunately, because coffee emits CO2 for days after it is roasted, one must allow the coffee to get slightly stale before it can be vacuum sealed. For this reason two technologies have recently been employed: Illy has begun to use pressurized cans and many roasters bag whole beans immediately after roasting in bags with pressure release valves . Today home roasting is becoming popular again. Computerized drum roasters are available which simplify home roasting, and some home roasters simply roast in an oven or in air popcorn poppers. Once roasted, coffee loses its flavor quickly. Although some prefer to wait 24 hours after roasting to brew the first cup, all agree that it begins to get off-flavors and bitterness about a week after roasting even under ideal conditions.
The fineness of the grounds has a major impact on flavour, with finer grinding leading to a more intense and full flavour. The main reason to use coarser grounds is simply to prevent the grounds from being pushed through coarser filter types (such as the cafetière).
There are two methods of producing coffee grounds ready for brewing.