Microstructural evolution of Ethiopian coffee beans by time-resolved X-ray microcomputed tomography

Coffee is one of the most widely consumed beverages in the world. Its flavor is influenced not only by the variety of the beans, but also by the growth environment, pre- and post-roasting processes, and roast levels. All these factors impact the chemical and microstructural properties of the bean. While the chemical composition of coffee beans has been well documented, the microstructural changes during roasting, which affect grinding and extraction processes, are less understood. In this study, we present a non-destructive quantification of the coffee bean’s microstructure as it undergoes roasting using non-destructive time-resolved X-ray computed tomography (4D-XCT). Pores within the roasted coffee bean have distinct shapes and orientations with clear spatial anisotropy, which is impacted by the degassing of volatiles during roasting; results show that pores near the bean’s outer surface are oriented outwards, while pores in central regions align at right angles to the near-surface pores.