## 1 Introduction  
Aging is a key process in the production of alcoholic beverages, driving the maturation of aroma and colour through complex chemical reactions that enhance their organoleptic quality [1]. Among the various aging techniques, bottle maturation is well-established, particularly for wines and liqueurs and is characterised by reactions affecting both volatile and non-volatile compounds, leading to transformations in the flavour and colour of the beverages [2]. The bottle aging process has been reported to involve three distinct stages. In the initial stage, maturation enhances the wine's characteristics, while the peak sensory quality is achieved during the second phase. However, extending the bottle aging period beyond this optimal window (third stage) can lead to a decline in quality [3; 4]. Volatile compounds play a crucial role in defining the wine's aroma. Numerous chemical reactions occur among these volatile compounds during bottle aging, modifying their composition and concentration and hence affecting the sensory attributes of wine [5]. Oxygen significantly influences these transformations, particularly through oxidation reactions, which affect both volatile and non-volatile components in aged wines [6; 7; 8]. For example, the oxidation of phenolic compounds during bottle aging contributes to sensory changes in wine, affecting its colour, taste and trigeminal sensations [9]. Moderate oxidation during bottle aging can lead to the conversion of ethanol into acetaldehyde, which further reacts with tannins or anthocyanins in the wine to form complex ethyl-linked compounds [10]. Furthermore, fruity aroma can diminish over time due to ester and acetate hydrolysis during aging, while oxidative aroma begins to emerge [11]. In contrast, long-chain esters, such as ethyl succinate, increase in concentration after the first year of aging and may gradually decrease in subsequent years [12]. Generally, a decrease in alcohols is also reported during bottle aging, likely due to their reaction with acids in a condensation process, leading to the formation of esters [13]. Other non-volatile substrates that play a critical role in the development of volatile compounds during aging are carotenoids. Over time, carotenoids can degrade to form norisoprenoids, such as TDN, \(\alpha\)-ionone and \(\beta\)-damascenone, which are key contributors to the characteristic aroma of long-aged wines, like Riesling, imparting distinctive kerosene-like notes [14]. Increased oxygen permeation into the bottle during aging can accelerate oxidative reactions, leading to the oxidation of ethanol through acetaldehyde into acetic acid, which can deteriorate the wine's quality after bottling [15]. Recently, sea underwater aging has emerged as a new aging method for wines and liqueurs. This approach takes advantage of the unique underwater conditions, including more stable temperature, gentle oscillatory movement, and moderate exposure to light, to influence the maturation processes. Preliminary results have shown that during underwater aging, Merlot wine maintains more stable levels of total phenolic compounds, which decrease at a slower rate compared to cellar aging [16]. Moreover, wine aged under the sea appears to better preserve the total anthocyanin content over the aging period. On the other hand, in Malvasia white wines, the total antioxidant capacity (ABTS and DPPH) and total phenol content (Folin-Ciocalteu) did not show significant differences between underwater and cellar aging, despite LC-MS/MS quantitative analysis revealed that wines aged in underwater springs exhibited significantly higher concentrations of naringenin and myricetin [17]. These studies were characterized by a short aging time, such as one week. Another recent study investigated a longer aging period, with wines aged for 6 months underwater followed by an additional 6 months in a cellar, compared to wines aged entirely in a cellar for 12 months [18].