Rice-Adulterated Roasting: How Traditional Practices Alter Acidity and Caffeine in Indonesian (Sumowono) Robusta Coffee (Coffea Canephora)

Coffee is a globally significant commodity, with Coffea canephora (robusta) accounting for 40–43% of production. Recent climate-induced yield declines have raised concerns about coffee quality and affordability. Traditional Indonesian practices, such as adding rice during roasting, offer potential solutions to modulate flavor and chemical composition. This study investigates the effects of rice adulteration (0–30% w/w) on the acidity and caffeine content of Sumowono Robusta coffee using UV-VIS spectrophotometry and pH analysis. Results show that increasing rice content reduces caffeine concentration by up to 8.4% (from 13.89 ppm to 12.72 ppm) and elevates pH from 5.4 to 6.3, indicating decreased acidity. The non-linear reduction in caffeine suggests starch-mediated binding, while the pH increase reflects rice’s buffering capacity. These findings validate indigenous techniques as a natural means to produce milder coffee while preserving cultural authenticity. The study bridges traditional knowledge with modern science, offering insights for sustainable coffee processing and potential market differentiation for Robusta producers. Further research should explore sensory impacts and optimize roasting protocols for broader application.