Impact of oak barrel aging on furfural formation in industrially produced grape brandy

Brandy is a traditional spirit widely produced in the Balkan region, where industrial production relies on rectification columns and oak barrel maturation to ensure consistent quality. This study investigated the evolution of furfural, a furanic aldehyde, during oak barrel aging of brandy produced from the Vranec grape variety, one of the most important cultivars in North Macedonia. Wines were obtained by controlled fermentation and subjected to double rectification distillation, yielding distillates containing 80–90% (v/v) ethanol. The distillates were diluted to 40% (v/v) ethanol and matured in medium-toast Hungarian oak barrels for 24 months. Furfural was quantified using a spectrophotometric method based on derivatization with an aniline acetate reagent, following preliminary distillation to eliminate color interferences. Measurements were performed at 0, 6, 12, 18, and 24 months of maturation. Fresh distillates already contained measurable furfural concentrations (0.56–1.12 mg.L-1), originating from thermal sugar degradation during distillation. During barrel aging, furfural concentrations increased progressively, reaching 2.12–3.22 mg.L-1 after 12 months. The most pronounced increase occurred between 12 and 18 months (3.44–6.89 mg.L-1). After 24 months, furfural levels stabilized, indicating a balance between extraction from oak wood and secondary reactions. These results suggest that furfural may serve as a useful indicator of maturation progress and sensory development in industrially produced brandy under the conditions investigated.