(600b) Evolution of Coffee Roasting

Based on the number of reaction products detected more than 700 flavor and aroma generating reactions occur during coffee roasting. Many parallel roasting reactions occur. Other important reactions occur in series. Some reaction products, e.g. volatile acids, partially decompose or are lost when coffee is over-roasted; others, e.g. phenols, pyridines, increase in concentration when roasting is excessively prolonged.

Though it is obviously a reaction proccess, roasting usually has been treated and analyzed primarily as a heating process. Recent work on roasting that has focussed on improving the rate and uniformity of heat transfer to individual beans and to the bean load as a whole and on better control of the heating process are described High bean heating rates, now widely utilized, have been accompanied by changes in the physical, chemical and sensory properties of roasted coffee beans and of ground roasted coffee derived from those beans.

Better control of bean heating and of temperature-dependent roasting reactions has been achieved by means of feedback control systems designed to control bean temperature versus time behavior during the course of roasting. Factors that must be accounted for in implementing such control are discussed.

Recent experimental results that provide bases for more realistically describing and modelling bean heating, roasting reaction kinetics and the thermophysocal properties of coffee beans are described and discussed.

Minimization or elimination of roasting generated pollutants, the desire to conserve energy, the rise of mini roasters and specialty roasters and niche demands have also influenced how coffee roasting has recently evolved.