Fermentation of green coffee beans is a promising method for enhancing coffee quality. However, to maintain the consistency of the coffee produced, a controlled and consistent process is required using a fermenter (fermentation vessel). This study aimed to evaluate the effect of ohmic heating (OH) and fermentation duration on the properties of coffee beans (Robusta variety). Experiments were performed by combining two factors: fermentation type (with and without OH) and fermentation duration (6, 12, and 18 h). The results showed that the fermentation time significantly affected the pH value of the fermented liquid, total acidity of the coffee, coffee bean colour, and caffeine content. OH-assisted fermentation reduced the caffeine content and increased the total acidity of Robusta coffee, with the 18-h treatment yielding the lowest caffeine content. Additionally, a sensory analysis using the Specialty Coffee Association of America method revealed that coffee produced using OH-assisted fermentation for 18 h resulted in a higher score of 82.75, classified as a specialty grade. This study suggests that OH-assisted fermentation could improve sensory quality and reduce caffeine content in Robusta green coffee beans, making it suitable for people who are sensitive to caffeine.