The production of jaggery and treacle from fermented Caryota inflorescence sap presents significant challenges. This study aimed to evaluate the effectiveness of extracts from the leaves, bark, and flowers of Acronychia pedunculata in inhibiting the fermentation of Caryota urens inflorescence sap and to determine the most effective part and concentration for this purpose. Essential oils were extracted from fresh plant parts (leaves, bark, and flowers) using hydro-distillation. These oils were applied to non-fermented Caryota inflorescence sap at four different concentrations to assess their effects on turbidity, pH, Brix value, alcohol content, and microbial growth. The results showed that the bark of Acronychia pedunculata yielded significantly more oil (13.67%) compared to the leaves (1.61%) and flowers (4.31%). Application of 2–3 ml of bark oil resulted in higher pH values in the Caryota sap. The highest mean alcohol content (2.09) and Brix value (8.87) were observed with 3 ml of bark oil, indicating effective fermentation inhibition. The lowest mean turbidity value (785.4) was also recorded with 3 ml of bark oil. Additionally, FTIR analysis suggested that the oils contained polyphenols (such as flavonoids and tannins) and terpenes. This study recommends Acronychia pedunculata bark oil as an effective fermentation inhibitor, providing valuable insights for enhancing the production of jaggery and treacle in Sri Lanka.