# Madeira Wine Volatile Profile. A Platform to Establish Madeira Wine Aroma Descriptors
## 1 Introduction  
Madeira wine is a fortified Portuguese wine produced in Madeira Island over the last centuries playing an important role in the Island economy. The specific characteristics of Madeira wine arise from a set of specific conditions including the terroir, unique grape varieties and the singular winemaking process. The fermentation process is stopped by the addition of natural grape spirit in order to obtain an ethanol content of 18-22% (_v/v_). Some wines are submitted to an aging process in oak casks, in cellars, at temperatures up to 30 \({}^{\circ}\)C, and humidity levels between 70 and 75%, while the majority of wines are submitted to a baking process, i.e., the wine is placed in large coated vats and the temperature is slowly increased at about 5 \({}^{\circ}\)C per day, and maintained at 45-50 \({}^{\circ}\)C for at least 3 months. After this treatment, the wine is allowed to undergo a maturation process in oak casks for a minimum of 3 years [1; 2]. Wine volatile composition plays an important role in wine quality since it promotes several sensations during wine consumption, odors (due to molecules that can bind olfactory receptors) and can affect flavor (combination of aroma and taste) in mouth retro-nasally, that lead to consumer acceptance or rejection. The wine aroma consists of a combination of several hundred of different volatile organic compounds (VOCs), most of which are present in trace amounts (usually at ug/L or ng/L level) [3]. Nevertheless, the presence of a molecule at a concentration above its odor threshold (OT), is sufficient to provide a characteristic product aroma (impact odorant). Nevertheless, even when present at concentrations below their OTs, may contribute to the overall wine aroma, as a result of the interactions with other molecules [4]. Different extraction techniques, such as solid phase extraction (SPE) [5; 6; 7; 8; 9] and liquid-liquid extraction [5; 10; 11; 12; 13] have been applied on the establishment of volatile profile of Madeira wine. However, most of these approaches present several disadvantages, such as time- and labor-intensive, large solvent and sample amount, which can lead to analyze losses and a reduction in sensitivity. Currently, the trend in the analyze of VOCs is more focused in the use of miniaturized sample preparation, increasing of efficiency of analysis, no solvent techniques, such as solid-phase microextraction (SPME) [7; 10; 14; 15], stir bar sorptive extraction (SBSE) [14] and microextraction by packed sorbents (MEPS) [7] followed by gas chromatography-mass spectrometry (GC-MS) process have been used for that purpose. GC-MS is user-friendly, fast, selective and very sensitive method to establish the volatile signature of several food matrices. In addition, it was also equipped with powerful data systems that are used not only to control and acquire data from the GC and MS, but also to identify flavor components by automated matching against reference libraries of spectra of known odorants [16]. The Madeira wines volatile composition has been topic of several studies, as the data obtained has been useful in the elucidation of basic flavor chemistry. Enormous efforts were focused on the topic of varietal (e.g., terpenoids, norisoprenoids) [14; 17; 18], pre-fermentative (e.g., C\({}_{6}\) alcohols and aldehydes) [11], fermentative (e.g., alcohols, esters, acids, carbonyl compounds) [5; 8; 14], and finally aging aroma compounds (e.g., volatiles extracted from oak, like volatile phenols, lactones) [5; 8; 15; 19]. Few studies have focused on the establishment of potential impact odorants, which could contribute individually to the Madeira wine aroma [6]. [PERSON] et al. [6] build a hierarchical list of the odorants using gas chromatography-olfactometry (GC-O) that express the aroma of Madeira wines. The GC-O profile of Madeira wines lacks on varietal compounds (e.g., terpenoids, cystein-derived thiols), is rich in sotolon, phenylacetaldehyde, (\(Z\))-whiskey lactone and of some volatile phenols (e.g., guaiacol, 4-vinylguaiacol, \(m\)-cresol).