## 6 Influence of Ageing Factors on the Coumarin Contents of Spirit Beverages
### Heat Treatment  
It is unquestionably accepted by the scientific community that the heat treatment of the wood, carried out during the cooperage process, plays a decisive role in the set of extractable compounds that can be released into the distillate during ageing (19; 23; 195). In Europe, a fire with wood scraps is used to bend the staves and then toast their inner surface, while in North America heated steam is used to bend the staves, followed by a fire or a gas burner for charring (in a controlled manner) the inner surface of the wood (199; 200; 201; 164; 195; 199; 201). Thus, in barrels made using the European technique, there is normally 6-8 mm of toasted wood, and in barrels made using the American technique there is normally 2-3 mm of charred wood followed by 3-5 mm of toasted wood. The aim of the bending phase is to give the barrel a concave shape without the staves breaking. The toasting phase is carried out intentionally to change the structure (202), physical properties (203) and chemical composition of the wood (2001; 2002; 201), thus imparting a particular character to the distillate aged in it. Though toasting procedures differ according to the cooperage, the toasting level is usually categorised as light, medium or heavy. The char (active charcoal) layer is required for some distillates, such as whiskey and cachaca, to decrease pungency and remove off-flavours associated with some constituents, such as sulphur compounds, through adsorption and oxidation (2000; 2001; 2002; 2003; 2004; 2005; 2006).  
Hydrothermolysis of the wood biopolymers (cellulose, hemicelluloses and lignin) and tannins mainly occurs during toasting, and leads to the formation of low-molecular-weight compounds (2001; 164), which can be easily extracted by the distillate during ageing, thus influencing its chemical composition and sensory properties. Cellulose gives rise to 5-hydroxymethylfurfural and 5-methylfurfural and hemicelluloses originate furfural, while lignin is the precursor of several phenolic compounds, including coumarins (2001). Ellagic acid and gallic acid result from the degradation of ellagitannins and gallotannins, respectively (2009). Subsequently, several reactions take place in the liquid medium, determining the features of the aged spirits (2001; 2002; 177; 190; 192). Regarding coumarins, in a recent study, [PERSON] et al. (2010) showed that scopoletin was thermolabile, and underwent degradation in a temperature range from 182.32 \({}^{\circ}\)C to 303 \({}^{\circ}\)C, with mass loss of 99.98%. Moreover, as far as we know, the effect of this technological factor on their contents has only been reported for wine spirits--Figure 17.  
The results showed that toasting had a significant effect on the average concentration of umbelliferone in wine spirit aged for four years in 250 L barrels; an increase in concentration was observed as the intensity of wood toasting rose, reflecting the accumulation of this compound in the wood, due to its remarkable thermal stability, which could then be extracted by the wine spirit (2011). The concentration of scopoletin was slightly affected, but the highest level was associated with medium toasting, suggesting that lower temperatures favoured its formation, and, as the toasting temperature increased, degradation phenomena exceeded the formation ones (2010). According to the works of [PERSON] et al. (2010) and [PERSON] et al. (2011), the umbelliferone demonstrated greater thermal stability than scopoletin.