Agricultural Rum of Madeira matured on the seafloor: improved physicochemical changes induced by a pioneering seafloor ageing process

The unique agricultural rum produced in Europe, Agricultural Rum of Madeira, is obtained from alcoholic fermentation and distillation of sugarcane juice, followed by cask ageing for a minimum of 3 years. For the first time, the impact of underwater bottle ageing on the maturation of this type of spirit was studied. Herein, the physicochemical properties of samples of Agricultural Rum of Madeira bottle-aged in a cellar and after 7 and 14 months on the seafloor were compared. The results revealed significant and positive changes in the organoleptic properties of the rum after 14 months of ageing on the seafloor. It was found that underwater ageing does not lead to the loss of the specific polyphenols of the cask-ageing stage (non-flavonoids, 43.53 mg/L after 14 months on the seafloor) and increases the flavonoids composition (6.88 to 21.09 mg/L after 14 months). While the acidity increased slightly, the volatile composition of the primary aromas resulting from sugarcane (terpenoids) was unchanged. Esters represented about 85% of the volatile compounds in the bottled sugarcane spirit after ageing in casks and higher concentration (increase of about 23%) were detected after underwater ageing. This study also revealed that 14 months of underwater ageing promoted a colour change to darker tones, with values close to those detected by the human eye (ΔE of 2.47). The principal component analysis highlighted the meaningful changes after 14 months on seafloor conditions, without any chemical family standing out as the most important.