Influence of Fermentation Water on Stable Isotopic D/H Ratios of Alcohol Obtained from Concentrated Grape Must

Abstract

<jats:p>According to Organisation Internationale de la vigne et du vin (OIV) standards, when analysing the stable isotope ratio of deuterium to hydrogen D/H at the methyl (I) and methylene (II) site of ethanol from concentrated must, a dilution with tap water is needed in order to carry out the alcoholic fermentation. This dilution causes a partial transfer of water hydrogens to the sugar, and this affects the (D/H)I and (D/H)II isotopic values of ethanol, which need to be normalised through specific equations based on the analysis of water δ18O or δ2H. The aim of this study was to evaluate the effectiveness and correctness of these equations experimentally. Grape, cane, and beet sugar, as well as grape must were diluted with water with increasing H and O stable isotope ratios, fermented, and analysed. SNIF-NMR and IRMS techniques were applied following the respective OIV methods. The equations based on the δ2H analysis of the diluted sugar/must solutions proved to be reliable in all the cases, although it is not an OIV standard. When using the equations based on the values of δ18O of the diluted solution, data normalisation was reliable only in cases where the water used for dilution had not undergone isotopic fractionation due, for example, to evaporation. In these cases, δ2H should be analysed.</jats:p>

Differentiation of Geographic Origin of South African Wines from Austrian Wines by IRMS and SNIF-NMR

“…This is remarkable, as this value is in the range of the lowest δ 13 C-values of wine from Austria (see below), which grows in a different climatic and geographical situation. The negative correlation of δ 13 C and (D/H)II (independent from cultivar, Figure 2 ) seems strange at first view, as higher δ 13 C-values denote more intense drought stress, and higher (D/H)II-values indicate higher 2 H-values of the (irrigation) water that the vines took up [ 8 , 36 ]. The latter implies either water from a high-temperature region, or highly evaporated water (water from a water body that has already lost a notable part of its water due to evaporation [ 37 , 38 ], and therefore, these parameters (drought stress and water evaporation) often correlate positively.…”

NMR in the Service of Wine Differentiation

“…Chaptalization with sugar from beetroot or another C 3 plant can still be observed, as the methyl site isotopic ratio is significantly lower in ethanol produced by fermentation of beetroot sugar when compared to ethanol derived from grapevine sugar [ 136 , 137 ]. The degree of chaptalization by beetroot sugar can be expressed from the following equation: where (D/H) I,s is the isotopic ratio of the sample after normalization for the deuterium content of water [ 138 ], (D/H) I,BEET is the mean value for the beet sugar reference (92.7 ppm), while (D/H) I,COP refers to the cutoff value of the ratio for the geographic origin of the specific sample [ 104 ]. Experimentally determined isotopic ratios are compared to the official national and international wine databanks when authentication and geographical grouping are performed [ 139 , 140 ].…”

Determining sugar and molasses origin by non‐exchangeable hydrogen stable isotope of ethanol and carbon isotope ratio mass spectrometry

“…In contrast, the relative proportion of hydrogen-stable isotopes of the methylene site of ethanol (D/H) II is in constant dynamic equilibrium with the surrounding water (water used in alcoholic fermentation) (Martin et al, 2001;Smajlović et al, 2013;Zhang et al, 2002). According to Perini et al (2020), the (D/H) I value depends on the sugar source (C 3 or C 4 plant) and provides information about its botanical origin, whereas the (D/H) II values depend on the water used in the fermentation medium. Additionally, the combination of δD n and δ 13 C values of ethanol allowed for the differentiation of various ethanol sources present in wine (Smajlović et al, 2013).…”

“…According to Perini et al. (2020), the (D/H) I value depends on the sugar source (C 3 or C 4 plant) and provides information about its botanical origin, whereas the (D/H) II values depend on the water used in the fermentation medium. Additionally, the combination of δ D n and δ 13 C values of ethanol allowed for the differentiation of various ethanol sources present in wine (Smajlović et al., 2013).…”