<P> 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 . Other pressurized water methods include the moka pot and vacuum coffee maker . </P> <P> Cold brew coffee is made by steeping coarsely ground beans in cold water for several hours, then filtering them . This results in a brew lower in acidity than most hot - brewing methods . </P> <P> Brewed coffee from typical grounds prepared with tap water contains 40 mg caffeine per 100 gram and no essential nutrients in significant content . In espresso, however, likely due to its higher amount of suspended solids, there are significant contents of magnesium, the B vitamins, niacin and riboflavin, and 212 mg of caffeine per 100 grams of grounds . </P> <P> Once brewed, coffee may be served in a variety of ways . Drip - brewed, percolated, or French - pressed / cafetière coffee may be served as white coffee with a dairy product such as milk or cream, or dairy substitute, or as black coffee with no such addition . It may be sweetened with sugar or artificial sweetener . When served cold, it is called iced coffee . </P>

Where does the us get its coffee from