Roasting Kinetics and Chemical Composition Changes of Robusta Coffee Beans During Hot Air and Superheated Steam Roasting

As it is known that Robusta coffee beans exhibit more bitterness, less acidity, and lacks sweetness with unbalance flavor as compared to their Arabica counterpart, a means to improve the quality of Robusta coffee beans is desirable. As a step that contributes to the coffee quality, it is interesting to determine if an alternative roasting technique could lead to the desired improved quality. Here, roasting kinetics and changes in pH and composition of Robusta coffee beans undergoing hot air and superheated steam (SHS) roasting at 190 to 250 degrees C were investigated. SHS roasting led to higher rates of bed temperature increase, moisture loss and decrease in lightness (L-* value) of the beans. Evolutions of the moisture content and L-* value of the beans could be well described by the adopted kinetic equations. pH, caffeine, sugars, and organic acids contents of the beans were significantly affected by the temperature and degree of roasting. Interestingly, beans roasted in SHS had lower pH, higher sucrose, glucose, and arabinose contents. Their fructose and acetic acid contents were nevertheless lower, indicating that the beans probably exhibited higher sweetness and citrus-like acidity, but lower unfavorable vinegar-like acidity.