Processing coffee consists of roasting, storage, preparation, and presentation.
Coffee berries and their seeds undergo multi-step processing before they become the roasted coffee with which most consumers are familiar. First, coffee berries are picked, generally by hand. Then, the flesh of the berry is removed, usually by machine, and the seeds—usually called beans—are fermented to remove the slimy layer of mucilage still present on the bean. When the fermentation is finished, the beans are washed with large quantities of freshwater to remove the fermentation residue, which generates massive amounts of highly polluted coffee wastewater. Finally, the seeds are dried, sorted, and labeled as green coffee beans. The next step in the process is the roasting of the green coffee. Coffee is usually sold in a roasted state, and all 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 but 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 200 °C (392 °F), though different varieties of beans differ in moisture and density and therefore roast at different rates. During roasting, caramelization occurs as intense heat breaks down starches in the bean, changing them to simple sugars that begin to brown, changing the color of the bean. Sucrose is rapidly lost during the roasting process and may disappear entirely in darker roasts. During roasting, aromatic oils, acids, and caffeine weaken, changing the flavor; at 205 °C (400 °F), other oils start to develop. One of these oils is caffeol, created at about 200 °C (392 °F), which is largely responsible for coffee!!!s aroma and flavor.
Once roasted, coffee beans must be stored properly to preserve the fresh taste of the bean. Ideal conditions are air-tight and cool. Air, moisture, heat and light are the environmental factors in order of importance to preserving flavor in coffee beans. Folded-over bags, a common way consumers often purchase coffee, is generally not ideal for long-term storage because it allows air to enter. A better package contains a one-way valve, which prevents air from entering.
Coffee beans must be ground and brewed in order to create a beverage. Grinding the roasted coffee beans is done at a roastery, in a grocery store, or in the home. They are most commonly ground at a roastery then packaged and sold to the consumer, though "whole bean" coffee can be ground at home. Coffee beans may be ground in several ways. A burr mill uses revolving elements to crush or tear the bean, an electric grinder chops the beans with blades moving at high speeds, and a mortar and pestle grinds the beans to a powder. 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 grind. The most common grinds are between the extremes; a medium grind is used in most common home coffee brewing machines. Coffee may be brewed by several methods: boiled, steeped, or pressured. Brewing coffee by boiling was the earliest method, and Turkish coffee is an example of this method. It is prepared by powdering the beans with a mortar and pestle, then adding the powder to water and bringing it to a boil in a pot called a cezve or, in Greek, a briki. This produces a strong coffee with a layer of foam on the surface. Machines such as percolators or automatic coffeemakers brew coffee by gravity. In an automatic coffeemaker, hot water drips onto coffee grounds held in a coffee filter made of paper or perforated metal, allowing the water to seep through the ground coffee while absorbing its oils and essences. Gravity causes the liquid to pass into a carafe or pot while the used coffee grounds are retained in the filter. In a percolator, boiling water is forced into a chamber above a filter by pressure created by boiling. The water then passes downwards through the grounds due to gravity, repeating the process until shut off by an internal timer. Coffee may also be brewed by steeping in a device such as a French press (also known as a cafetière). Ground coffee and hot water are combined in a coffee press and left to brew for a few minutes. A plunger is then depressed to separate the coffee grounds, which remain at the bottom of the container. Because the coffee grounds are in direct contact with the water, all the coffee oils remain in the beverage, making it stronger and leaving more sediment than in coffee made by an automatic coffee machine. The espresso method forces hot, but not boiling, pressurized water through ground coffee. As a result of brewing under high pressure (ideally between 9-10 atm) the espresso beverage is more concentrated (as much as 10 to 15 times the amount of coffee to water as gravity brewing methods can produce) and has a more complex physical and chemical constitution. A well prepared espresso has a reddish-brown foam called crema that floats on the surface. The drink "Americano" is popularly thought to have been named after American soldiers in WW II who found the European way of drinking espresso too strong. Baristas would cut the espresso with hot water for them.
Once brewed, coffee may be presented in a variety of ways. Drip brewed, percolated, or French-pressed/cafetière coffee may be served with no additives (colloquially known as black) or with either sugar, milk or cream, or both. When served cold, it is called iced coffee. Espresso-based coffee has a wide variety of possible presentations. In its most basic form, it is served alone as a "shot" or in the more watered-down style café américano—a shot or two of espresso with hot water. The Americano should be served with the espresso shots on top of the hot water to preserve the crema. Milk can be added in various forms to an espresso: steamed milk makes a cafè latte, equal parts espresso and milk froth make a cappuccino, and a dollop of hot, foamed milk on top creates a caffè macchiato.
A number of products are sold for the convenience of consumers who do not want to prepare their own coffee. Instant coffee is dried into soluble powder or freeze dried into granules that can be quickly dissolved in hot water. Canned coffee has been popular in Asian countries for many years, particularly in Japan and South Korea. Vending machines typically sell varieties of flavored canned coffee, much like brewed or percolated coffee, available both hot and cold.