Effect of Particle Size on Color of Ground Coffee

Introduction: Particle size is one of the main variables that influence coffee brewing process and also most obvious to the consumers. The aim of this study was to evaluate the effect of different particle sizes on the color of ground coffee.

Methods: A laser diffraction analyzer was used to determine the particle size distribution of the 14 dry ground coffee samples. The particle size distribution of the roasted ground coffee samples that underwent grinding at different time periods was based on volume distribution. Color measurements of all coffee samples were made using a portable CR-400 tristimulus colorimeter and Spectra-Match software, set to L*, a*, b* mode. Color measurements were recorded for two replicates of each sample.

Results: Coffee samples ground for short times of 30s, 20s and 10s, were observed to have coarser particles than those that underwent longer grinding times. The 20s and 30s grinding times did not exhibit any significant differences for the D50 and D90 particle size distributions. There was no significant difference in D50 and D90 values for Colombian 1.3, Leyenda and Tarrazu brands. It was observed that lightness (L*) as well as a* and b* were highly significantly different between the different coffee samples with P < 0.0001. The coffee samples that underwent grinding for 60s had the highest L*, a* and b* values of 30.72, +1.31 and +1.39 respectively. Colombian 1.3 coffee brand had the lowest L* and a* values of 29.8 and +0.67 respectively, with brand 1820a having the lowest b* value of +0.39.

Conclusion: The results of this study show that there was no significant effect of particle size distribution of coffee samples on color of the ground coffee particles. L*, a* and b* values decreased during roasting, due to the darkening of the beans resulting from sugar caramelization and Maillard reactions.