Plymouth Electron Microscopy Centre
We were lucky enough to go on an adventure with our speciality coffee beans on the train for a day out with the wonderful team at the Plymouth Electron Microscopy Centre to analyse the beans to delve into how exposure to heat from the wood roasting process affects the microstructure.
We decided to take the Ethiopia Heirloom from our Pink Label single origin range for the analysis due to the lot being a monovarietal which would allow for a fair comparison at the different stages of the roast. We took 16 batches of samples; each sample meticulously taken at every minute of the roasting process from the pre-roast green beans to the post roast de-gassed beans. As a roastery we are accustomed to witnessing the transition of colour during the roasting process from green to light brown to dark brown. Yet, we were genuinely intrigued to uncover what valuable insights the scientists could provide us regarding the impact on the beans' microstructure.
From each batch, two beans were selected for analysis – one was cut in half to reveal its internal cross-section, while the other was kept whole to analyse its surface. Each bean was mounted onto a metal stub and coated with gold, rendering the surface conductive and microscope-ready. The team then proceeded with the analysis using a cutting-edge scanning electron microscope, capturing intricate grey-scale photographs of the beans' microstructure.
The analysis of the coffee beans at different stages of the roasting process revealed some interesting findings:
1. Changes in Microstructure: The microstructure of the beans changed significantly as the roasting process progressed. At the beginning of the process, when the beans were green, they had a dense structure with few pore spaces. However, as the roasting continued, the beans developed more pore spaces, indicating the release of gas (likely carbon dioxide) during the roasting and degassing process.
2. External Surface Textures: The top surfaces of the beans, when analysed under the same conditions and instrument, remained relatively consistent throughout the roasting process. There were no clear variations in microstructure observed on the external surface.
3. Cross-Sectional Analysis: When examining the cross-section of the beans, it was evident that the fully roasted beans had abundant pore spaces. These spaces likely resulted from the release of air during the roasting process as the beans came into contact with heat.
4. Wrinkled and Cracked Texture: All beans displayed a wrinkled, sometimes cracked texture on the top surface, with the central crease of the bean consisting of bladed and spiral textures. This texture is common in roasted coffee beans.
Overall, the study showed the progressive changes in the microstructure of coffee beans during the roasting process, including the development of pore spaces and the release of gas. The findings contribute to a better understanding of the physical changes that occur in coffee beans during roasting and how these changes might affect the final product's flavour and quality. The analysis was conducted as part of the fully ERDF and University of Plymouth funded Plymouth Materials Characterisation Network project, which collaborated with PEMC for the scanning electron microscopy analysis of the beans.
Read the PECM on their website here
