Effect of acetic acid immersion on the taste and aroma quality of immature Robusta coffee beans

The presence of immature coffee beans reduces the quality of the coffee brew. This study evaluated how the acetic acid affected the aroma and taste of immature compared to mature Robusta coffee. The naturally processed immature Robusta green beans were immersed in acetic acid (0-5%) for 30-90 min. The naturally processed mature Robusta green beans were used as a control treatment. The samples were roasted at a medium level (240 °C, 14 min). The sensory analysis was evaluated by the cupping test by a trained and certified panellist (Q-Grader). Acetic acid immersion significantly improved the sensory quality of immature beans (P < 0.05). Specifically, immersion in 3% acetic acid for 90 min yielded the highest sensory score of 84.92. According to the Coffee Quality Institute (CQI) classification, this score falls into the 'Fine' Robusta classification. The 0% 30-min, 3% 30-min, and 3% 90-min treated immature samples and an untreated control mature sample were analysed for pH, caffeine, chlorogenic acid, and volatile compounds. The treatment significantly decreased the chlorogenic acid (P < 0.05) and increased the volatile compound concentration of furans, ketone, pyrrole, aldehyde, and ester while decreasing pyrazines, sulphur, phenol, and alcohol. This study effectively enhanced immature Robusta taste and aroma quality to a degree comparable with mature Robusta coffee beans.