A coffee bean (Arabic بُن bunn) is a misnomer for a seed of a coffee plant. It is the pit inside the red or purple fruit often referred to as a cherry. Even though they are seeds, they are incorrectly referred to as 'beans' because of their resemblance to true beans. The fruits - coffee cherries or coffee berries - most commonly contain two stones with their flat sides together. A small percentage of cherries contain a single seed, instead of the usual two. This is called a peaberry. Like Brazil nuts (a seed) and white rice, coffee seeds consist mostly ofendosperm.^[1]

The two most economically important varieties of coffee plant are the Arabica and the Robusta; 75-80% of the coffee produced worldwide is Arabica and 20% is Robusta.^[1] Arabica seeds consist of 0.8-1.4% caffeine and Robusta seeds consist of 1.7-4% caffeine.^[2] As coffeeis one of the world's most widely consumed beverages, coffee seeds are a major cash crop, and an important export product, counting for over 50% of some developing nations' foreign exchange earnings.^[3] The United States imports more coffee than any other nation.^[4] In 2009 the average person in the United States consumed 4.09 kg (9 lbs) of coffee.^[5]

Coffee plant

The coffee tree averages from 5–10 m (15–30 ft.) in height. As the tree gets older, it branches less and less and bears more leaves and fruit. The tree typically begins to bear fruit 3–4 years after being planted, and continues to produce for 10–20 more years, depending on the type of plant and the area.

Coffee plants are grown in rows several feet apart. Some farmers plant fruit trees around them or plant the coffee on the sides of hills, because they need specific conditions to flourish. Ideally, Arabica coffee seeds are grown at temperatures between 15-24°C and Robusta at 24-30°C and receive between 1500-3000mm (60–120 in)of rainfall per year.Heavy rain is needed in the beginning of the season when the fruit is developing, and less later in the season as it ripens. The harvesting period can be anywhere from three weeks to three months, and in some places the harvesting period continues all year round

Processing

Coffee berries

When the fruit is ripe, it is almost always handpicked, using either selective picking, where only the ripe fruit is removed or strip-picking, where all of the fruit is removed from a branch all at once. Because a tree can have both ripe and unripe berries at the same time, one area of crop has to be picked several times, making harvesting the most labor intensive process of coffee bean production.

There are two methods of processing the coffee berries. The first method is wet processing, which is usually carried out in Central America and areas of Africa. The flesh of the berries is separated from the seeds and then the seeds are fermented – soaked in water for about two days. This dissolves any pulp or sticky residue that may still be attached to the seeds. They are then washed and dried in the sun, or, in the case of commercial manufacturers, in drying machines.

Roasted coffee seeds

The dry processing method is cheaper and simpler, used for lower quality seeds in Brazil and much of Africa. Twigs and other foreign objects are separated from the berries and the fruit is then spread out in the sun on cement or brick for 2–3 weeks, turned regularly for even drying. The dried pulp is removed from the seeds afterward.

After processing has taken place, the husks are removed and the seeds are roasted, which gives them their varying brown color, and they can then be sorted for bagging.

Coffee roasting

Coffee roasting machine

Light roasted coffee beans

Dark roasted coffee beans

Roasting coffee transforms the chemical and physical properties of green coffee beans into roasted coffee products. The roasting process is what produces the characteristic flavor of coffee by causing the green coffee beans to expand and to change in color, taste, smell, and density. Unroasted beans contain similar acids, protein, and caffeine as those that have been roasted, but lack the taste. Heat must be applied for the Maillard and other chemical reactions to occur.

As green coffee is more stable than roasted, the roasting process tends to take place close to where it will be consumed. This reduces the time that roasted coffee spends in distribution, giving the consumer a longer shelf life. The vast majority of coffee is roasted commercially on a large scale, but some coffee drinkers roast coffee at home in order to have more control over the freshness and flavor profile of the beans

Process

The coffee roasting process follows coffee processing and precedes coffee brewing. It consists essentially of sorting, roasting, cooling, and packaging but can also include grinding in larger scale roasting houses. In larger operations, bags of green coffee beans are hand or machine-opened, dumped into a hopper, and screened to remove debris. The green beans are then weighed and transferred by belt or pneumatic conveyor to storage hoppers. From the storage hoppers, the green beans are conveyed to the roaster. Roasters typically operate at temperatures between 240–275 °C (464–527 °F), and the beans are roasted for a period of time ranging from 3 to 30 minutes.^[1] Initially, the process is endothermic (absorbing heat), but at around 175 °C (347 °F) it becomes exothermic (giving off heat).^[2]For the roaster, this means that the beans are heating themselves and an adjustment of the roaster's heat source might be required. At the end of the roasting cycle, the roasted beans are dumped from the roasting chamber and cooled with forced air. Sometimes, in large commercial roasters, the beans are first quenched with a fine water mist. Torrefacto is a roasting process used in Spain and parts of Latin America involving the addition of sugar.

[edit]Equipment

The most common roasting machines are of two basic types: drum and hot-air, although there are others including packed bed, tangential and centrifugal roasters. Roasters can operate in either batch or continuous modes.

Drum machines consist of horizontal rotating drums that tumble the green coffee beans in a heated environment. The heat source can be supplied by natural gas, liquefied petroleum gas (LPG), electricity, or even wood. The most common employ indirectly heated drums where the heat source is under the drum. Direct-fired roasters are roasters in which a flame contacts the beans inside the drum; very few of these machines are still in operation.

Hot-air roasters force heated air through a screen or perforated plate under the coffee beans with sufficient force to lift the beans. Heat is transferred to the beans as they tumble and circulate within this fluidized bed.

[edit]Degree of roasting

Coffee roasters use names for the various degrees of roast, such as City Roast and French Roast, for the internal bean temperatures found during roasting. Roastmasters often prefer to follow a "recipe" or "roast profile" to highlight certain flavor characteristics. Any number of factors may help a person determine the best profile to use, such as the coffee's origin, variety, processing method, or desired flavor characteristics. A roast profile can be presented as a graph showing time on one axis and temperature on the other, which can be recorded manually or using computer software and data loggers linked to temperature probes inside various parts of the roaster.

[edit]Determining degree of roast

The most popular, but probably the least accurate, method of determining the degree of roast is to judge the bean's color by eye (the exception to this is using a colorimeter to measure the ground coffee reflectance under infrared light and comparing it to standards such as the Agtron scale). As the beans absorb heat, the color shifts to yellow and then to increasingly darker shades of brown. During the later stages of roasting, oils appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source. Beans will also darken as they age, making color alone a poor roast determinant. Most roasters use a combination of bean mass temperature, smell, color, and sound to monitor the roasting process.

Sound is a good indicator of bean temperature during roasting. There are two temperature thresholds called "cracks" that roasters listen for. At about 205–207 °C (401–405 °F), beans will emit a cracking sound much like popcorn does when it pops, only much quieter. This point is called "first crack," marking the beginning of light roasts. When the beans are at about 224–227 °C (435–441 °F), or a medium roast, they emit a "second crack." This is the dividing point between medium and dark roasts.

[edit]Degree of roast pictorial

These images depict samples taken from the same batch of a typical Brazilian green coffee at various bean temperatures with their subjective roast names and descriptions.^[3]^[4]^[5]

	22 °C (72 °F) Green Beans Green coffee beans as they arrive at the dock. They can be stored for up to two years.		165 °C (329 °F) Drying Phase As beans roast, they lose water and increase in size. Arabian coffee is prepared using beans roasted from between 165 °C (329 °F) and 210 °C(410 °F).
	195 °C (383 °F) Cinnamon Roast A very light roast level, immediately before first crack. Light brown, toasted grain flavors with sharp acidic tones, almost tea-like in character.		205 °C (401 °F) New England Roast Moderate light brown, still acidic but not bready, a traditional roast for Northeastern U.S. Coffee, at first crack.
	210 °C (410 °F) American Roast Medium light brown, the traditional roast for the Eastern U.S. First crack ending.		220 °C (428 °F) City Roast Medium brown, the norm for most of the U.S., good for tasting the varietal character of a bean.
	225 °C (437 °F) Full City Roast Medium dark brown with occasional oil sheen, good for varietal character and bittersweet flavors. At the beginning of second crack.		230 °C (446 °F) Vienna Roast Moderate dark brown with light surface oil, more bittersweet, caramel-y flavor, acidity muted. In the middle of second crack. Occasionally used for espresso blends.
	240 °C (464 °F) French Roast Dark brown, shiny with oil, burnt undertones, acidity diminished. At the end of second crack. A popular roast for espresso blends.^[6]		245 °C (473 °F) Italian Roast Very dark brown and shiny, burnt tones become more distinct, acidity almost gone, thin body. The common roast for espresso blends.^[7]
	250 °C (482 °F) Spanish Roast Extremely dark brown, nearly black and very shiny, charcoal and tar tones dominate, flat, with thin body.

[edit]Caffeine content by roast level

Caffeine content varies by roast level. Caffeine diminishes with increased roasting level: light roast, 1.37%; medium roast, 1.31%; and dark roast, 1.31%.^[8] However, this does not remain constant in coffee brewed from different grinds and brewing methods.

[edit]Roast flavors

At lighter roasts, the bean will exhibit more of its "origin flavor"; the flavors created in the bean by its variety, the soil, altitude, and weather conditions in the location where it was grown.^[9]

Coffee beans from famous regions like Java, Kenya, Hawaiian Kona, and Jamaican Blue Mountain 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.

Below, roast levels and their respective flavors are described.^[10] These are qualitative descriptions, and thus subjective. As a rule of thumb, the "shinier" the bean is, the more dominant the roasting flavors are.

	Roast level	Notes	Surface	Flavor
Light	Cinnamon roast, half city, New England	After several minutes the beans “pop” or "crack" and visibly expand in size. This stage is called first crack. American mass-market roasters typically stop here.	Dry	Lighter-bodied, higher acidity, no obvious roast flavor
Medium	Full city, American, regular, breakfast, brown	After a few short minutes the beans reach this roast, which U.S. specialty sellers tend to prefer.	Dry	Sweeter than light roast; more body exhibiting more balance in acid, aroma, and complexity. Smoother than the traditional American "medium" roast, but may display fewer of the distinctive taste characteristics of the original coffee.^[11]
Full Roast	High, Viennese, Continental	After a few more minutes the beans begin popping again, and oils rise to the surface. This is called second crack.	Slightly shiny	Somewhat spicy; complexity is traded for heavier body/mouth-feel. Aromas and flavors of roast become clearly evident.
Double Roast	French	After a few more minutes or so the beans begin to smoke. The bean sugars begin to carbonize.	Very oily	Smokey-sweet; light bodied, but quite intense. None of the inherent flavors of the bean are recognizable.