The diffusion kinetics of carbon dioxide in fresh roasted and ground coffee

Carbon dioxide is produced as a result of many reactions that take place during roasting of coffee. Although some carbon dioxide is released during roasting and upon grinding, some is trapped and slowly released creating a packaging problem. Either vacuum packaging to prevent a billowing of the package or special film to release CO₂ from inside the package are required. In addition, the coffee is usually tempered in order to maximize release of CO₂ before packaging. In this research, the diffusion kinetics of carbon dioxide release from fresh roasted and ground coffee during tempering were determined. The CO₂ degassing results fit a series expansion of Fick's law for unsteady state diffusion using either one or two effective diffusivities based on an analysis of transport mechanisms. The calculated effective diffusivity was between 0.5 and 10 × 10^-13 m²/s. It appears that pressure flow and Knudsen diffusion take place and are important during tempering.