Coffee berries, which contain the coffee seeds or "beans", are produced by several species of small evergreen bush of the genus Coffea. The two most commonly grown are the highly regarded Coffea arabica, and the "robusta" form of the hardier Coffea canephora. Once ripe, coffee berries are picked, processed, and dried. The seeds are then roasted to varying degrees, depending on the desired flavor. They are then ground and brewed to create coffee. Coffee can be prepared and presented in a variety of ways.
Coffee berries and their seeds undergo several processes before they become the familiar roasted coffee.
The berries are sorted by ripeness and color and most often the flesh of the berry is removed 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 fresh water to remove the fermentation residue. 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. Most African coffee is dried in this manner and certain coffee farms around the world are starting to use this traditional method.
Another way to let the coffee beans dry is to let them sit on a concrete patio and rake over them in the sunlight. Some companies use cylinders to pump in heated air to dry the coffee beans, though this is generally in places where the humidity is very high.
Next, the coffee is sorted, and labeled as green coffee.
The next step in the process is the roasting of the green coffee. 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 requirements for packaging.
The actual roasting begins when the temperature inside the bean reaches approximately 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.
During roasting, aromatic oils and acids weaken, changing the flavor; at 205 °C (401 °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.
Many coffee companies have specialized terminology for their different roasts and there is not much industry standardization. The different names for flavored roasts can cause confusion, but in general, the types of roasts fall into one of four color categories: light, medium, medium-dark, dark.
The degree of roast has an effect upon coffee flavor and body. 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.
Once roasted, coffee beans must be stored properly to preserve the fresh taste of the bean. Ideally, the container must be airtight and kept in a cool, dry and dark place. In order of importance: air, moisture, heat, and light are the environmental factors responsible for deteriorating flavor in coffee beans.
Folded-over bags, a common way consumers often purchase coffee, are generally not ideal for long-term storage because they allow air to enter. A better package contains a one-way valve, which prevents air from entering.
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 the beans to be ground and mixed with hot water long enough to extract the flavor, but without over-extraction that draws out unnecessary bitter compounds. The spent grounds are removed and the liquid is consumed. There are many variations in the fineness of grind, the ways in which the water extracts the flavor, additional flavorings (sugar, milk, spices), and spent ground separation techniques. The ideal holding temperature is 79 to 85 °C (174 to 185 °F) and the ideal serving temperature is 68 to 79 °C (154 to 174 °F).
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 the extremes; a medium grind is used in most common home coffee-brewing machines.
Coffee may be brewed by several methods: boiled, steeped, or pressurized.
Brewing coffee by boiling was the earliest method, and Turkish coffee is an example of this method. It is prepared by grinding or pounding the beans to a fine powder, then adding it to water and bringing it to the boil for no more than an instant in a pot called a cezve or, in Greek, a bríki. This produces a strong coffee with a layer of foam on the surface and sediment (which is not meant for drinking) settling on the bottom of the cup.
Coffee percolators and automatic coffeemakers brew coffee using gravity. In an automatic coffeemaker hot water drips onto coffee grounds held in a coffee filter made of paper, plastic, or perforated metal, allowing the water to seep through the ground coffee while extracting its oils and essences. The liquid drips through the coffee and the filter into a carafe or pot, and the spent grounds are retained in the filter.
Coffee may be brewed by steeping in a device such as a French press (also known as a cafetière or coffee press). Ground coffee and hot water are combined in a cylindrical vessel and left to brew for a few minutes. A circular filter which fits tightly in the cylinder fixed to a plunger is then pushed down from the top to force the grounds to the bottom. 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 pressurized and vaporized 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 quantity 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