By: David Nield
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Critics:
Coffee berries are traditionally selectively picked by hand, which is labor-intensive as it involves the selection of only the berries at the peak of ripeness. More commonly, crops are strip picked, where all berries are harvested simultaneously regardless of ripeness by person or machine. After picking, green coffee is processed by one of two types of method a dry process method which is often simpler and less labor-intensive, and a wet process method, which incorporates batch fermentation, uses larger amounts of water in the process, and often yields a milder coffee.
Then they are sorted by ripeness and color, and most often the flesh of the berry is removed, usually by machine, and the seeds are fermented to remove the slimy layer of mucilage still present on the seed. When the fermentation is finished, the seeds are washed with large quantities of fresh water to remove the fermentation residue, which generates massive amounts of coffee wastewater.
Finally, the seeds are dried. The best (but least used) method of drying coffee is using drying tables. In this method, the pulped and fermented coffee is spread thinly on raised beds, which allows the air to pass on all sides of the coffee, and then the coffee is mixed by hand. The drying that then takes place is more uniform, and fermentation is less likely.
Most African coffee is dried in this manner and certain coffee farms around the world are starting to use this traditional method. Next, the coffee is sorted, and labeled as green coffee. Some companies use cylinders to pump in heated air to dry the coffee seeds, though this is generally in places where the humidity is very high. An Asian coffee known as kopi luwak undergoes a peculiar process made from coffee berries eaten by the Asian palm civet, passing through its digestive tract, with the beans eventually harvested from feces.
Coffee brewed from this process is among the most expensive in the world, with bean prices reaching $160 per pound or $30 per brewed cup. Kopi luwak coffee is said to have a uniquely rich, slightly smoky aroma and flavor with hints of chocolate, resulting from the action of digestive enzymes breaking down bean proteins to facilitate partial fermentation. In Thailand, black ivory coffee beans are fed to elephants whose digestive enzymes reduce the bitter taste of beans collected from dung.
These beans sell for up to $1,100 a kilogram ($500 per lb), achieving the world’s most expensive coffee, three times costlier than palm civet coffee beans. The next step in the process is the roasting of green coffee. Coffee is usually sold in a roasted state, and with rare exceptions, such as infusions from green coffee beans, coffee is roasted before it is consumed.
It can be sold roasted by the supplier, or it can be home roasted. The roasting process influences the taste of the beverage by changing the coffee bean both physically and chemically. The bean decreases in weight as moisture is lost and increases in volume, causing it to become less dense. The density of the bean also influences the strength of the coffee and the requirements for packaging.
The actual roasting begins when the temperature inside the bean reaches approximately 200 °C (392 °F), though different varieties of seeds differ in moisture and density and therefore roast at different rates. During roasting, caramelization occurs as intense heat breaks down starches, changing them to simple sugars that begin to brown, which darkens the color of the bean.
Sucrose is rapidly lost during the roasting process, and may disappear entirely in darker roasts. During roasting, aromatic oils and acids weaken, changing the flavor; at 205 °C (401 °F), other oils start to develop. One of these oils, caffeol, is created at about 200 °C (392 °F), and is largely responsible for coffee’s aroma and flavor. The difference of caffeine content between a light roast and a dark roast is only about 0.1%.
Depending on the color of the roasted beans as perceived by the human eye, they will be labeled as light, medium light, medium, medium dark, dark, or very dark. A more accurate method of discerning the degree of roast involves measuring the reflected light from roasted seeds illuminated with a light source in the near-infrared spectrum.
This elaborate light meter uses a process known as spectroscopy to return a number that consistently indicates the roasted coffee’s relative degree of roast or flavor development. Coffee has, in many countries, been graded by size longer than it has been graded by quality. Grading is generally done with sieves, numbered to indicate the size of the perforations.The degree of roast affects coffee flavor and body.
The color of coffee after brewing is also affected by the degree of roasting. Darker roasts are generally bolder because they have less fiber content and a more sugary flavor. Lighter roasts have a more complex and therefore perceived stronger flavor from aromatic oils and acids otherwise destroyed by longer roasting times.
Roasting does not alter the amount of caffeine in the bean, but does give less caffeine when the beans are measured by volume because the beans expand during roasting. A small amount of chaff is produced during roasting from the skin left on the seed after processing. Chaff is usually removed from the seeds by air movement, though a small amount is added to dark roast coffees to soak up oils on the seeds. Decaffeination of coffee seeds is done while the seeds are still green.
Many methods can remove caffeine from coffee, but all involve either soaking the green seeds in hot water (often called the “Swiss water process”) or steaming them, then using a solvent to dissolve caffeine-containing oils. Decaffeination is often done by processing companies, and the extracted caffeine is usually sold to the pharmaceutical industry.
Coffee is best stored in an airtight container made of ceramic, glass or non-reactive metal. Higher quality prepackaged coffee usually has a one-way valve that prevents air from entering while allowing the coffee to release gases. Coffee freshness and flavor is preserved when it is stored away from moisture, heat, and light. The tendency of coffee to absorb strong smells from food means that it should be kept away from such smells.
Storage of coffee in refrigerators is not recommended due to the presence of moisture which can cause deterioration. Exterior walls of buildings that face the sun may heat the interior of a home, and this heat may damage coffee stored near such a wall. Heat from nearby ovens also harms stored coffee. In 1931, a method of packing coffee in a sealed vacuum in cans was introduced. The roasted coffee was packed and then 99% of the air was removed, allowing the coffee to be stored indefinitely until the can was opened.
Today this method is in mass use for coffee in a large part of the world. Coffee beans must be ground and brewed to create a beverage. The criteria for choosing a method include flavor and economy. Almost all methods of preparing coffee require that the beans be ground and then mixed with hot water long enough to allow the flavor to emerge but not so long as to draw out bitter compounds. The liquid can be consumed after the spent grounds are removed.
Brewing considerations include the fineness of the grind, how the water is used to extract the flavor, the ratio of coffee grounds to water (the brew ratio), additional flavorings such as sugar, milk, and spices, and the technique to be used to separate spent grounds. Optimal coffee extraction occurs between 91 and 96 °C (196 and 205 °F). Ideal holding temperatures range from 85 to 88 °C (185 to 190 °F) to as high as 93 °C (199 °F) and the ideal serving temperature is 68 to 79 °C (154 to 174 °F).
Coffee beans may be ground in various ways. A burr grinder uses revolving elements to shear the seed; a blade grinder cuts the seeds with blades moving at high speed, and a mortar and pestle crush the seeds. For most brewing methods a burr grinder is deemed superior because the grind is more even and the grind size can be adjusted. The type of grind is often named after the brewing method for which it is generally used.
Turkish grind is the finest grind, while coffee percolator or French press are the coarsest grinds. The most common grinds are between these two extremes: a medium grind is used in most home coffee-brewing machines.
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