Coffee Roasting is a combination of science and art.
Green coffee bean has no flavor and the desired flavor only occurs during roasting. The goal of roasting is to optimize the flavors of coffee`s soluble chemistry. Dissolved solids make up brewed coffee`s taste, while dissolved volatile aromatic compounds and oils are responsible for aroma.
Kaufman observed that pressure formed in the beans during roasting is necessary to the proper development of coffee flavor. He also noticed the change in pH during roasting. The initial pH of 5,8 in green coffee drops at first to 4.8 and rises again. The optimum roast being shortly after the min. pH value. When measuring coffee`s acidity as pH, a lower pH value indicates higher acidity, and a higher value indicates lower acidity.
Acidity gives coffee it`s liveliness, delicacy, complexity and brightness. Coffee without acid is flat and boaring.
Roasting steadily breaks down Chlorogenic acid (CGA), with 50% remaning in a light roast and perhaps 20% in a dark roast.
Chlorogenic acid (CGA) contributes to the astringency and body; sucrose contributes to the aroma, color, sourness and bitterness; proteins remain perfectly stable.
Raw coffee`s sucrose content has a strong influence on it`s potential acidity and sweetness after roasting. Sucrose contributes to acidity because it’s caramelization yields acetic acid.
During roasting more than 800 aroma compounds are formed by Strecker and Maillard reactions as predominant reactions.