Impact of aging on dimethyl sulfide (DMS) in Corvina and Corvinone wines

Abstract

Amarone is an Italian red wine produced in the Valpolicella area, in north-eastern Italy. Due to its elaboration with withered grapes, Amarone is a rather unique example of dry red wine. However, there is very limited data so far concerning the volatile composition of commercial Amarone wines, which also undergo a cask aging of 2-4 years before release. The present work aims at characterizing the aroma composition of Amarone and to elucidate the relationships between chemical composition and sensory characters.  Two sets of Amarone wines from different vintages 2015 (17 wines) and 2016 (15 wines) were analyzed. The analyses were carried out by means of Gas Chromatography-Mass Spectrometry (GC-MS) and extracted by Solid Phase Extraction (SPE) and Solid Phase Micro Extraction (SPME). In addition, the sampled wines were subjected to a sensory evaluation in the form of sorting task. From both data sets, 70 volatile compounds were successfully identified and quantified, 30 of which were present in concentrations above their odor thresholds in all the samples. Using the odor activity value (OAV), the compounds that potentially contribute to Amarone perceived aroma are b-damascenone, ethyl and isoamyl acetate, ethyl esters (hexanoate, octanoate, butanoate, 3-methybutanoate), 4-ethyl guaiacol, 3-methylbutanoic acid, dimethyl sulfide (DMS), eugenol, massoia lactone, 1,4-cineol, TDN, cis-whisky lactone. The only differences found between the two vintages’ OAV list, could be observed in the presence of dimethyl trisulfide (DMTS) in the vintage 2015; whereas in the 2016 set g-nonalactone and trans-whisky lactone were found. Regarding the compounds that impart the most differences across both vintages, OAV max/min, where 4- ethyl phenol, 4-ethyl guaiacol, 1,8-cineole, 1,4-cineole, dimethyl sulfide (DMS). Results from the sorting task sensory analysis of the 17 wines from vintage 2015 showed three clusters formed. Cluster 1 composed of eight wines and described as “red fruit”, “solvent” and “sweet spices”. Cluster 2 formed by four Amarone was associated mainly with the “animal” and “oak/toasted” attributes. And cluster 3 (five wines) described with the attribute “cooked fruit”. While in the sorting task of vintage 2016 (15 wines) two clusters were formed: cluster A formed by 5 wines described as “cooked fruit” and “solvent”; and cluster B (10 wines) associated with the attributes “sweet spices”, “red fruit” and “oak/toasted”. To our knowledge the present research is the first attempt to identify and classify Amarone della Valpolicella commercial wines in terms of aroma. This study provides a list of compounds that can be characteristic of Amarone wine and that have been consistent across two vintages coming from different wineries . Moreover, from the volatiles analyzed, compounds such as dimethyl sulfide (DMS) and cineoles have been singled out as potential aroma markers of diversity in Amarone wines. Dimethyl sulfide (DMS) is a low molecular weight sulfur compound produced in wine during aging by the chemical degradation of S-Methyl-L-methionine (SMM). Investigating the aromatic profile of Amarone commercial wines from different wineries, it was found that DMS presented a high variation in concentration across wine samples ranging from 2.88 to 64.34 μg/L, which potentially can affect the perceived aroma. Therefore, in order to investigate this variation, the influence of grape variety, withering, precursor and vintage on DMS formation was studied. To achieve this a set of experimental wines, vintage 2017, 2018 and 2019 made with Corvina and Corvinone (fresh and withered) grapes from five different vineyards was submitted to accelerated aging. Samples in duplicate were kept at 45 °C for 24, 48, and 96 days, and then analyzed by HS-SPME GC-MS to determine their DMS content.Results showed minor increases in all samples at 24 and 48 days, whereas a considerable accumulation of DMS occurred at 96 days with concentrations approaching values around 120 μg/L. Additionally, it was observed that wines made from withered grapes presented higher concentrations respect to those made with fresh grapes, while the grape variety did not show a significant difference. The precursor influence in the wines was explored as well through the correlation between DMS concentration and primary amino acid nitrogen (PAN) content in wines (before aging). PAN content was measured at 340 nm in an automatic analyzer. In wines from vintage 2017, a good correlation (R2=0.7742) was found between the DMS (concentration of DMS at 96 days minus initial concentration) and PAN. While for wines from vintage 2018 and 2019, the correlation was 0.5581 and 0.4043, respectively. Finally, in order to further elucidate additional factors related to the variability in the ability of wines to generate DMS during aging, the influence of pH was also investigated. For this, two sets of wine, one spiked with SMM, were submitted to an accelerated aging (one month, 45 °C), in which pH was adjusted to 3 and 4. Results showed an increase in DMS of 10% in the samples with pH 4, which could be explained by the stability of SMM in acid conditions, therefore, at a higher pH the precursor could be more prone to release DMS.  Concluding, this study points out PAN as a potential tool to predict the production of DMS during aging. As well as providing some indications of the influence of withering in DMS production.