Degassing kinetics and sorption equilibrium of carbon dioxide in fresh roasted and ground coffee

Carbon dioxide produced by both the Strecker degradation reaction (Maillard reaction) and carbohydrate pyrolysis during high temperature roasting of coffee, and trapped in the fresh roasted and ground (FRG) coffee, is one of the major problems in the industry. Coffee solids can entrap or sorb up to 10 mL CO₂/g. The eventual evolution of this carbon dioxide during storage after packaging in flexible films can cause the bursting of the package. A good understanding of the mechanism that governs carbon-dioxide evolution and equilibrium in FRG coffee will provide true control over carbon dioxide release and equilibrium in the package. The objective of this study was to establish the equilibrium parameters of carbon-dioxide sorption/desorption, and determine the rate of carbon-dioxide diffusion from the ground coffee. Carbon dioxide sorption in FRG coffee is best described by the Langmuir isotherm. A higher degree of roasting resulted in an increase of CO₂ sorption in the coffee. The degassing kinetics of CO₂ from FRG coffee followed an exponential pattern, described by a series expansion function, which forms the basis for the simplified Crank solution. The range of diffusivities of the various roasts was at 10^-14 to 10^-15 m²/s. The temperature effect on the diffusivity can be described by the Arrhenius equation, with activation energy of 73.6 kJ/mole.