Frontal Inverse Gas Chromatography as Used in Studying Water Sorption of Coffee Solubles

Frontal Inverse Gas Chromatography (FIGC) was used to study the combined effects of moisture, temperature, and particle size on the water sorption of freeze-dried coffee. A moisture increase from 0 to 95% RH resulted in typical anti-Langmuirian sorption isotherms. Lower temperatures favored sorption at equivalent water vapor pressures. The mesh size of coffee had only a slight effect on the amount of sorbed water at higher relative humidities but did affect FIGC. A comparison of the FIGC and static methods showed that the former was much faster and the sorption isotherms of the two methods were statistically different.