## 2 Materials and Methods  
### Samples and Solutions  
The distillate used for testing was obtained from virgin Moscato pomace, fermented and distilled, according to the method employed for grappa production [15]. The raw distillate, with an alcohol content of 70% \(v/v\), was diluted to obtain an alcohol content of approximately 40% before chip infusion; a volume of 7.5 L of this solution was divided into 15 aliquots. Each sample had a final volume of 500 mL. Each one, apart from control, contained oak (12 samples) or poplar (2 samples) wood fragments of differing sizes and toasting levels for us to assess their impact on the final aromatic composition of the spirit (Table 1).  
To investigate how the wood affected the release of aromatic compounds during infusion, three different formats of alternative products were considered, of 2.5 mm (peeled wood), 0.56 mm (sliced wood) and 18.0 mm (cubes or wood tablets) in thickness, respectively.  
The samples of alternative woods were treated ad hoc by simulating the process steps adopted for large-scale production:  
* Seasoning of wood: Wood was immersed in deionized water, to reproduce the leaching action achieved by atmospheric precipitations during the open-air seasoning of staves used to produce barriques. The permanence time, submerged in water, was different for veneers and tablets (veneers, 1 h; tablets, 6 h; two washing cycles). Wood fragments were then stored in an oven at 25-30 \({}^{\circ}\)C, to simulate the environmental conditions of wood permanence outdoors during \"natural seasoning\";
* Toasting phase: Three different levels of heating were considered, non-toasted samples (NT), light toasting (50 \({}^{\circ}\)C for 15 min) and heavy toasting (180 \({}^{\circ}\)C for 50 min).  
A barrel generally has a surface-to-volume ratio ranging between 80-90 cm\({}^{2}\)/L; this ratio was applied to select the wood quantities to use for each 500 mL sample.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample Code** & **Toasting Level** & **Format** & **Ageing Conditions** & **Wood** \\ \hline
1 & NT 1 & peeled wood & room temperature & poplar \\
2 & heavy & peeled wood & room temperature & poplar \\
3 & NT & peeled wood & room temperature & oak \\
4 & heavy & peeled wood & room temperature & oak \\
5 & light & peeled wood & room temperature & oak \\
6 & NT & peeled wood & climatic chamber & oak \\
7 & heavy & peeled wood & climatic chamber & oak \\
8 & light & peeled wood & climatic chamber & oak \\
9 & NT & sliced wood & room temperature & oak \\
10 & heavy & sliced wood & room temperature & oak \\
11 & light & sliced wood & room temperature & oak \\
12 & NT & wood tablets & room temperature & oak \\
13 & heavy & wood tablets & room temperature & oak \\
14 & light & wood tablets & room temperature & oak \\
15 & control & control & room temperature & control \\ \hline \hline \end{tabular} \({}^{\dagger}\)NT: not toasted.  
\end{table}
Table 1: Experimental plan adopted during the study.  
The \"peeled wood\" samples, subjected to the three different levels of toasting, were replicated twice. A first set of samples (3, 4 and 5 in Table 1) was kept at room temperature during the refining phases, and another set of samples (6, 7 and 8 in Table 1) was stored in a climatic chamber at a controlled temperature and a constant relative humidity of 65%. The following temperature cycle was performed in order to simulate the typical excursion temperature in a refining cell. The cycle was carried out for about 12 months, and the first set of samples was stored at room temperature for the same period:  
- A temperature of 5 \({}^{\circ}\)C for 8 days;  
- A temperature of 15 \({}^{\circ}\)C for 8 days;  
- A temperature of 30 \({}^{\circ}\)C for 8 days;  
- A temperature of 15 \({}^{\circ}\)C for 8 days;  
- A temperature of 5 \({}^{\circ}\)C for 8 days.  
Samples were then stored in a temperature-controlled chamber protected from light.