Rethinking the ageing process of spirits: Nutshells as a sustainable alternative to wood

Aguardente bagaceira, a Portuguese grape marc spirit (GMS), represents an opportunity for sustainable innovation in ageing process. This study investigates the use of nutshells (almond, hazelnut, walnut, chestnut) as alternative ageing materials to conventional wood. Spirits were aged for six months in 20 L stainless steel vessels (50 g/L, chestnut tested at 12.5 and 25 g/L). An unaged sample and oak wood chips served as controls. Total phenolics (TPC), tannins (TAN), flavonoids (TF), pH, acidity, dry extract, and chromatic characteristics were monitored monthly. GMS aged with chestnut shells showed the highest levels of TPC (2.02 ± 0.17 g GAE/L), TAN (1.91 ± 0.07 g/L) and TF (0.250 ± 0.007 g CE/L) among the tested materials. Sensory analysis highlighted enhanced flavour complexity in chestnut-aged GMS after three months. These results demonstrate the potential of nutshells as sustainable, circular-economy alternatives to oak in spirit ageing, reducing ageing time without compromising quality.