Infrared and infrared-convective drying of foamed coffee extract for the instant coffee production: kinetics, energy-environmental performance and modeling study

The global demand for instant coffee has been rising due to its convenience and substantial sector investments. This study evaluated the use of a combination of infrared (IR) radiation and unheated air convection to dry foamed coffee extract. Foam drying enables lower temperatures and shorter times, features that have been associated in the literature with improved product quality and potential energy-related benefits. The foamed extract with 6 °Brix and 0.241 ± 0.038 g/cm 3 of density exhibited a stability of 96.93 ± 0.99%. Drying was performed using pure IR (118 - 238 W) and convection-assisted IR drying using unheated air (1.0 to 3.0 m s −1 ). Drying mainly occurred during the constant-rate period, and both methods produced powders meeting Brazilian regulations limiting moisture to 5%. Drying kinetics were well described by a two-period model distinguishing constant and falling rate periods. and h m ranged from 7.14×10 −7 to 4.23×10 −6 m 2 s −1 and from 0.0085 to 0.028 m s −1 , respectively. The hybrid method proved particularly advantageous, especially at higher IR power levels. The addition of airflow reduced the surface temperature of the material, preventing overheating, and improving moisture removal due to the air movement. Specifically, M f ranged from 0.96% (238 W; 2.0 m s −1 ) to 5.33% (118 W; 3.0 m s −1 ). Under these conditions, the minimum and maximum SEC and CO 2 emissions were also obtained, respectively (10.17 MJ kg -1 and 4.97×10 -6 CO 2 ; 26.06 MJ kg -1 and 1.41×10 -5 ton CO 2 ). • Infrared-convective drying of foamed coffee extract is promising for instant coffee. • Drying time decreased with higher IR power and was little affected by air velocity. • Adding air flow prevented overheating and enhanced surface moisture removal. • Higher P reduces final moisture content, SEC, and CO 2 emissions of instant coffee. • D eff and h m were successfully estimated using a two-period model.