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What X-Rays Reveal Inside a Coffee Bean
See a genuine micro-CT bean section, how roasting changes internal pores, and what tracking the same bean reveals about pore size and porosity.
Quick Answer
X-ray microcomputed tomography, or micro-CT, reconstructs the three-dimensional interior of a coffee bean from X-ray views taken at different angles. It reveals pores and cracks, and lets researchers follow structural changes during roasting.
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From Projections to a Three-Dimensional Bean
The Carnegie Mellon X-ray CT facility's explanation describes collecting X-ray projections from multiple directions and reconstructing a three-dimensional volume computationally. A displayed virtual slice is a view through that volume, so the bean can remain intact during scanning.
The enlarged section below comes from Al-Shemmeri and colleagues' 2024 coffee-bean study. It is a binary view: image processing has separated the bean interior into pore space and cellular material. Within the bean, this study shows pores in black and cellular material in white. The 1 mm scale bar puts the fine internal pattern into perspective.
This slice shows one plane through the reconstructed bean. A cavity's outline can change across neighboring slices, which together describe its three-dimensional shape. A whole-volume rendering combines those layers; colors in a void-space rendering may identify computed classes rather than the natural color of the bean.
Following the Same Bean Through Roasting
During roasting, the bean loses moisture, gases form and the structure expands. Changes in the cellular material and the development of internal pores accompany that expansion. Micro-CT lets researchers examine those changes inside the bean as well as its changing exterior.
Ganju and colleagues' 2024 study followed individual Arabica beans sourced from Brazil, Colombia and Ethiopia at green, light-roast and dark-roast stages. Pore space and pore size increased, but not in proportion to roasting time. Following the same bean connects its later structure with its own earlier state, instead of comparing the endpoint of one bean with the starting point of another.
Pore Size and Porosity Are Not Interchangeable
Pore size concerns the dimensions of individual spaces. Porosity is the fraction of a defined volume occupied by void space. Several small pores and a few larger pores can occupy a similar fraction of that volume.
As a two-dimensional area analogy, three circles with twice the radius of a small circle have the same combined area as twelve small circles. The circles illustrate how individual size and total occupied space differ. Bean porosity uses void volume in three dimensions.
Studying a Selected Region Answers a Different Question
Al-Shemmeri and colleagues' 2024 research measured a selected volume beneath the furrow of Kenyan Arabica beans roasted under different conditions. Beans with similar surface color could have different porosity. That supplies information about the interior beyond roast appearance and helps describe the physical changes needed for heat-and-mass-transfer modeling.
The analysis distinguishes open pores, which connect to the boundary of the selected volume, from closed pores, enclosed by cellular material. The classification uses the selected region's boundary; an open pore there does not necessarily lead all the way to the bean's exterior.
A personal note: The inside view is what catches my attention, but the choice of view is what keeps it. I want to know whether I am looking at a slice, a whole volume or a small selected region. Those are different ways of meeting the same object, and none feels less interesting once it has a clear label. A familiar coffee bean becomes more remarkable when I can follow how the image was made, rather than being asked to accept a dramatic picture as its own explanation.
What a Coffee Drinker Can Take from This Research
Micro-CT adds an internal view to the surface color you can see on roasted beans. These studies explain physical changes during roasting; choosing a coffee to drink still comes back to the finished cup. The roast-level guide connects roast descriptions with flavor and buying choices.
Sources
- Carnegie Mellon University, X-ray Computed Tomography Facility. X-ray computed tomography.
- Ganju, E., Chawla, K., Yang, S., and Chawla, N. (2024). Time-resolved roasting-induced microstructural evolution of Arabica coffee beans from Brazil, Colombia, and Ethiopia captured using x-ray computed micro-tomography. Journal of Food Engineering 361, 111733. DOI: 10.1016/j.jfoodeng.2023.111733.
- Mark Al-Shemmeri, Peter Fryer, Robert Farr and Estefania Lopez-Quiroga (2024). Development of coffee bean porosity and thermophysical properties during roasting. Journal of Food Engineering 378, 112096. DOI: 10.1016/j.jfoodeng.2024.112096. Figure 17 reproduced unchanged. Open paper, licensed under CC BY 4.0.