Physicochemical properties of Robusta coffee at various roasting levels using different roaster types

Abstract

Coffee roasting is the process to bring out flavors of green coffee beans by applying heat through the chemical changes. The objective of this study was to investigate the effect of roasting process at various levels using different types of roasting machine on the physicochemical properties of robusta coffee beans. Coffee beans were roasted using two types of roasting machine, namely semi-hot air and hot air. The roast levels used in this study include: light, medium, and dark. The results showed that the types of roasting machine only had a significant effect on the color of coffee powder. Coffee powder produced by a semi-hot air roasting machine had a higher L∗, a∗ and b∗ values (43.29-53.63; 5.54-11.09; 7.99-18.58). The roast level factor had a significant effect on bulk density of coffee beans, water content, ash content, caffeine levels and color of coffee powder. The bulk density, water content, and color (L∗, a∗, b∗ values) decreased, however ash content and caffeine levels tended to increase with the increase of roasting level. The coffee produced in this study had a bulk density ranging from 0.41-0.52 g/ml, a water content ranging from 1.24-2.57%, ash content ranging from 4.53- 5.00% and caffeine level ranging from 1.86-2.02%.