## 4 Sources of Coumarins  
Coumarins have been isolated from hundreds of plant species belonging to more than 40 families [117], and in several parts/tissues: leaves [118], flowers [119], fruits [117, 120], seeds [121], stems [122], wood [38, 123, 124], inner bark [112] and roots [125, 126]. Indeed, phenolic compounds play a significant role in the intricate defence mechanism of plants, and their biosynthesis is triggered by abiotic stress, such as UV radiation and ozone [127, 128, 129, 108], and biotic stresses such as infections and wounding [108, 130, 131]. For these reasons, coumarins are considered phytoalexins; some of these compounds have been found in high concentrations, while others, as is usually the case with coumarins, even in low concentrations, are involved in the plant's defence [104, 132]. Coumarins are found in the raw materials used in the production of spirit beverages addressed in this work: (i) grapes [133] and wine [22, 134] in grape marc spirit, wine spirit and brandy manufacture; (ii) cereal seeds [135, 136] in whiskey manufacture; (iii) sugar cane [137] in rum and cachaca manufacture. However, they are not released from the wine, the grape marc or the _wash_ into the steam during distillation, and consequently, they are not present in the corresponding distillates. Thus, the only source of coumarins is the wood used in their ageing. In accordance with the literature, among the many coumarins found in plants, those present in wood used for the ageing of spirit beverages are shown in Table 1, and their structures are elucidated in Figure 16. \begin{table}
\begin{tabular}{c c c c c} \hline
**Source** & **Species’ Country of Origin** & **Compound** & **Mean Content** & **References** \\ \hline \multirow{8}{*}{Oak_Quercus robur L.} & & scopoletin & 65 \(\mu\)g/L & [38] \\  & & scopoletin & 4.7 \(\mu\)g/g FW & [123] \\  & & France Limousin & scopoletin & 5.28 \(\mu\)g/g DW & [124] \\  & & umbelliferone & 0.006 \(\mu\)g/g DW & [124] \\  & & aesculetin & 1.68 \(\mu\)g/g FW & [138] \\ \cline{2-5}  & & Bulgaria & scopoletin & 125 \(\mu\)g/L & [38] \\  & & Spain & aesculetin & 2.1 \(\mu\)g/g FW & [138] \\  & & Croatia & aesculin & 0.44 \(\mu\)g/g FW & [139] \\  & & Serbia & aesculin & 0.22 \(\mu\)g/g FW & [139] \\  & & Bosnia and Herzegovina & aesculin & 0.11 \(\mu\)g/g FW & [139] \\ \hline \multirow{8}{*}{Oak_Quercus sessiliflora Salisb.} & & scopoletin & 55 \(\mu\)g/L & [38] \\  & & scopoletin & 3.6 \(\mu\)g/g FW & [123] \\ \cline{1-1}  & & France Allier & scopoletin & 3.45 \(\mu\)g/g DW & [124] \\ \cline{1-1}  & & umbelliferone & 0.006 \(\mu\)g/g DW & [124] \\ \cline{1-1}  & & aesculetin & 1.97 \(\mu\)g/g FW & [138] \\ \cline{1-1} \cline{2-5}  & & Spain & aesculetin & 4.2 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Serbia & aesculin & 0.44 \(\mu\)g/g FW & [139] \\ \hline Oak & Spain & scopoletin & 1.08–5.61 \(\mu\)g/g FW & [140] \\ \cline{1-1}  & & aesculetin & 1.60 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Portugal & scopoletin & 1.37 \(\mu\)g/g DW & [124] \\ \cline{1-1}  & & umbelliferone & 0.006 \(\mu\)g/g DW & [124] \\ \hline Oak & & Spain & aesculetin & 4.9 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Spain & aesculetin & 4.2 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Serbia & aesculin & 0.44 \(\mu\)g/g FW & [139] \\ \hline Oak & & Spain & scopoletin & 1.08–5.61 \(\mu\)g/g FW & [140] \\ \cline{1-1}  & & aesculetin & 1.60 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Portugal & scopoletin & 1.37 \(\mu\)g/g DW & [124] \\ \cline{1-1}  & & umbelliferone & 0.006 \(\mu\)g/g DW & [124] \\ \hline Oak & & Spain & aesculetin & 4.9 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Spain & aesculetin & 4.2 \(\mu\)g/g FW & [138] \\ \cline{1-1}  & & Serbia & aesculin & 0.44 \(\mu\)g/g FW & [139] \\ \hline \end{tabular}
\end{table} 
Table 1: Sources of coumarins. The results attained for coumarins in these studies clearly reveal the differences imparted by the botanical species. Moreover, variation in their concentrations within each kind of wood is observed.