Ever since that famous 13th-Century Ethiopian shepherd noticed his flock acting in a more animated fashion after eating the fruit of the coffee plant and then made a drink by grinding and brewing its seeds, coffee and chemistry have been inseparable. A typical cup of coffee contains over a thousand chemicals. The temperature of the brewing water—cold, room temperature, warm or boiling—has a profound effect on the flavor of the finished product. Steeping time, likewise, has a significant impact on the quality of the finished product. Pressure plays a big role, and even such seemingly trivial factors as filter material and whether to cover the pot while brewing have their say in the final cup. Many people take coffee quite seriously and believe wholeheartedly what others shrug off—that brewing technique has much (though not everything) to do with how good (or bad) that cup of coffee tastes.
Heat And The Coffee Bean
Heat has an effect on nearly all foods, and coffee is no different, especially in its acidic nature. Coffee grounds contain a surprising amount of acids—quinic, caffeic, citric, acetic and malic acid, to be precise—and each of these simple chemical compounds plays an important role in the development of a brewing pot of coffee’s complex flavor profile. (Malic acid, for example, particularly advances the “fruity” notes of a cup of coffee.) The significance of this is that overheated water will release unpleasant amounts of acid from the coffee bean, and good coffee is a result of getting the correct acidic contribution. Temperature also affects which solids are extracted during brewing, because solids dissolve more quickly at higher temperatures. Therefore, the ideal water temperature (somewhere between 195 and 202 degrees) is one that dissolves the most flavorful solids and the least unpleasant ones.
Time And The Coffee Bean
Perhaps the factor in brewing easiest to understand is time—that is, the amount of time the grounds spend in contact with hot water. The extraction of solids (oils, acids, caffeine and the like) from the grounds by the water increases over time, implying that an ideal time exists to achieve the best level of extraction. Each of the variety of brewing methods—brief boiling (Turkish), steeping (French press), overnight (cold brew), filtering (drip coffee), and pressurized (espresso)—has its own optimal brewing time, so first determine which method you prefer, and then begin the hard work of zeroing in on that perfect brew time!
Pressure And The Coffee Bean
Espresso is the brewing technique that raises the bar (so to speak) on the concept of pressure and its effect on extraction. A typical commercial espresso machine pressurizes water to 9 bar (meaning nine times the atmospheric pressure at sea level), while machines designed for home use generally measure in the 15 bar range. Espresso’s strong flavor is achieved through pressurizing the water and forcing it through a densely packed “puck” of grounds, resulting in greater yields of caffeine, flavor notes, and all the rest. (In this 2012 study, Arabica and Robusta espressos measured in at 141-253 mg of caffeine per 100 mL.)
While some might not categorize the following under “technique,” these minor factors do come into play during the brewing process: type of filter, whether metal, cloth or paper; cleanliness of equipment, as old oils will add unpleasant taste to the finished cup; and quality of water and whether it is soft or hard (water softeners remove metallic ions such as magnesium and calcium, which are necessary for optimum extraction during brewing).