## 2 Materials and Methods  
### Experimental Design and Sampling of WSs  
The 15 experimental units were placed in the cellar of Adega Cooperativa da Lourinha (Lourinha, Portugal) in 2017, in the same environmental conditions, and filled with the same freshly distilled wine spirit produced in a column still (alcoholic strength, 77.40 \(v/v\); pH, 5.44; total acidity, 0.13 g acetic acid/hL of absolute ethanol; volatile acidity, 0.11 g acetic acid/hL of absolute ethanol) from this producer.  
The experimental units of this trial, carried out on an industrial scale and based on a factorial design (two ageing technologies \(\times\) two blending technologies), are shown in Figure 1.  
The 250 L new barrels and the wood staves inserted into the 1000 L stainless steel tanks were made by [PERSON] M. Goncalves cooperage (Palacoulo, Portugal) from Limousin oak wood (L; _Quercus robur_ L.) and chestnut wood (C; _Castanaea sativa_ Mill.). The medium plus toasting level of both kinds of wood was assured by an accurate control of the wood's temperature: 90 min at an average temperature of 240 \({}^{\circ}\)C resorting to a fire of wood scraps for the barrels and to an industrial oven for the staves.  
In each ageing technology (b--barrels, traditional; a--tanks with wood staves inside, alternative), the two kinds of wood were used separately (C and L) and simultaneously  
Figure 1: Trial scheme. Blends B1–B3 were produced by blending operation of WSs from chestnut barrels (Cb) and Limousin oak barrels (Lb), at 50:50 ratio, after 18 months of ageing. Mb1–Mb3 were obtained by natural blending of WS (barrels comprising chestnut and Limousin oak staves, at 50:50 ratio, alternatively arranged) during 18 months of ageing. Blends B4 and B5 were produced by the blending operation of WSs from tanks with chestnut staves inside combined with MOX (Ca) and from those with Limousin oak staves inside combined with MOX (La), at 50:50 ratio, after 18 months of ageing. Ma1 and Ma2 were obtained by natural blending of WS (tanks comprising chestnut and Limousin oak staves inside, at 50:50 ratio, alternatively arranged, combined with MOX) during 18 months of ageing.  
(M, 50:50 ratio with staves alternately arranged). The M modalities correspond to the natural blending.  
The quantity of staves used in the tanks mimics the surface area/volume ratio of a 250 L barrel (85 cm\({}^{2}\)/L). During ageing, MOX was applied to the WSs stored in the tanks, supplying pure oxygen (X50S Food, Gasin, Portugal) at 2 mL/L/month flow rate by a micro-oxygenation with several ceramic diffusers (VISIO 6, Vivelys, France) [14].  
After 18 months of ageing, the WSs resulting from the natural blending (Mb1, Mb2, Mb3, Ma1 and Ma2) were bottled.  
At the same time, the WSs aged separately in chestnut barrels and in Limousin oak barrels were blended at 50:50 ratio (blends B1, B2 and B3), and those aged separately in tanks with chestnut staves and in tanks with Limousin oak staves were also blended at a 50:50 ratio (blends B4 and B5), as depicted in Figure 1. Barrels and tanks were randomly selected for the blending operation (B1-B5).  
Four bottles of each blend were kept in the cellar of Polo de Dois Portos--INIAV at 19 \({}^{\circ}\)C and 80% relative humidity for four months. Then they were sampled and analysed; a total of 10 samples were taken: B1, B2, B3, Mb1, Mb2, Mb3, B4, B5, Ma1 and Ma2.