coffee valveknows the taste of coffee is affected by many factors, the most essential factor is roasting. In brief, coffee roasting is a chemical change under high temperature, it can totally change the substance inside which make coffee bean generates new compound and different aroma.
Roasting is an art and science, a profound learning. So some experienced,skillful baristas in Europe own high reputation.
Coffee roasting is divided into three stages.
At the beginning of roasting, coffee beans absorb the heat, the moisture inside coffee beans evaporate slowly. During this stage, the color of coffee turns from green to yellow to light brown, grey involucra falls down and release a whiff of grass. This stage is for removing the redundant moisture inside coffee beans, it commonly takes half of the whole roasting time. Experienced barista can fully control temperature, moisture and prevent the moisture being evaporated too fast.
When the temperature of roasting reach 160℃, the moisture inside coffee beans is evaporated into steam. During this time, the heat absorbed by coffee beans is given off, and the first crack appears. After the first crack, the coffee beans absorb heat again, and the high pressure reach 25 par inside. High temperature and high pressure break the original struture of coffee beans, a new substance forms, the rich aroma and tasty are the ramification. When the temperature is 190 ℃, coffee beans absorb heat and the second crack appears. If the roasting continues, coffee beans will turn from brown to dark brown, dark roasting begins.
Coffee beans should be cooled for maintaining aroma and taste after being roasted. There are two methods to cool them: air cooling and cold water cooling.