## 6 Influence of Ageing Factors on the Coumarin Contents of Spirit Beverages
### Ageing Technology  
Traditionally, the spirit beverages are aged in wooden barrels for several months or years, in consonance with the producing-region regulation, as mentioned above. Despite the high quality of the final products obtained through this technology, it presents the following drawbacks: (i) it is time-consuming; (ii) it is costly; (iii) there is low production efficiency and profitability for the producer; (iv) there is substantial loss of the spirit beverage by evaporation, which is more pronounced in tropical areas such as those related to sugar-cane spirit production; (v) there is significant demand for wood, which is a  
Figure 18: Evolution of coumarin contents in spirit beverages over the ageing time: (**a**) whiskey (adapted from [PERSON] and [PERSON] [35]); (**b**) wine spirit (adapted from [PERSON] [214]); (**c**) wine spirit (adapted from [PERSON] et al. [37]); (**d**) cachaca (adapted from [PERSON] et al. [44]).  
limited-supply natural resource [23; 24; 44; 215]. Several research teams have therefore been looking for alternative technologies to move towards more sustainable production processes; the most widely exploited consists of using stainless-steel tanks with wood pieces inside and micro-oxygenation as an option [28; 30; 41; 42; 69; 114; 216; 217; 218; 219; 220]. In these studies, the assessment of the technologies' performances has been made by analysing the physicochemical characteristics (basic chemical parameters, volatile compounds, phenolic compounds, and mineral elements) and sensory properties acquired by the distillates during ageing. Among the phenolics, phenolic acids, phenolic aldehydes and tannins have been often scrutinised, which has not been the case with coumarins. The results available for coumarins are presented below.  
[PERSON] et al. [42] compared the scopoletin and umbelliferone contents in wine spirits obtained from the same _Lourinha_ distillate aged for 12 months in 250 L barrels of chestnut wood (B), in 50 L demijohns with staves of the same wood combined with three micro-oxygenation modalities (oxygen was applied with a flow rate of 2 mL/L/month for 15 days--O15, 30 days--O30, and 60 days--O60, followed by 0.6 mL/L/month until the end of the trial) and one control modality using nitrogen (N), with two replicates. The outcomes are shown in Figure 19.  
The wine spirits aged through the alternative technology, regardless of the micro-oxygenation modality, were significantly richer in umbelliferone than those aged using the traditional one and the control. On the other hand, the scopoletin level was significantly higher in the wine spirits from the barrels and the control. The oxygen applied (alternative technology) seems to have contributed to the balance between the additive and subtractive phenomena involving umbelliferone. As for scopoletin, the outcomes suggest that micro-oxygenation contributed to shifting this balance towards the subtractive phenomena, thus decreasing its content in the corresponding wine spirits.  
These results corroborate those of a previous project [41; 165], in which a _Lourinha_ distillate was aged in 250 L barrels and in 1000 L stainless steel tanks with wood staves inside, combined with a single micro-oxygenation flow rate (2 mL/L/month), for 18 months. It should be stressed that they suggest a different sensitivity of these coumarins to oxidation, since the direct supply of oxygen through micro-oxygenation favours oxidation reactions involving phenolic compounds [28]. Scopoletin seems to have enhanced susceptibility to oxidation compared to umbelliferone.  
Figure 19: Average contents of coumarins in wine spirits aged in barrels (B), in demijohns with wood staves and micro-oxygenation (O15, O30 and O60) and nitrogen (N, control) (adapted from [PERSON] et al. [42]). Bars marked with different letters denote significant differences (Fisher’s test; \(p<0.05\)).