The effect of stopping alcoholic fermentation on the variability of H, C and O stable isotope ratios of ethanol M. Perini * , R. Guzzon, M. Simoni, M. Malacarne, R. Larcher, F. Camin Fondazione Edmund Mach (FEM), Via E. Mach 1, 38010 San Michele all’Adige, Italy article info Article history: Received 16 October 2013 Received in revised form 13 December 2013 Accepted 14 December 2013 Keywords: Stable isotope Stopping fermentation Sweet wine Misinterpret Isotopic ratio mass spectrometry abstract Stopping fermentation using chemical or physical agents is an oenological procedure carried out in order to leave a pleasant amount of residual sugar in the wine. This process is typically used in the production of some Italian sweet wines (such as the famous Moscato d’Asti), where alcoholic fermentation is stopped once the alcoholic content reaches 4.5e10%. In this study, we investigated the effect of stopping fermentation on the isotopic values of (D/H) I , (D/H) II , d 13 C and d 18 O of ethanol obtained from wine. We examined 126 samples obtained by partially fermenting five different must samples (N ¼ 4 fresh musts, N ¼ 1 desulphited must) and 18 commercial Italian sweet wines. Fermentation stage was positively correlated with the d 13 C and, in particular, the (D/H) II values of ethanol, but not with the (D/H) I and d 18 O values. Partially fermented musts and traditional sweet wines were characterized by lower d 13 C and (D/ H) II isotopic values. The (D/H) II values were outside the normal range of variability for natural wines, which means that particular care must be taken in assessing the (D/H) II of sweet wines in order to avoid misinterpreting the results. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The quality of many marketed products is guaranteed by the imposition of precise legal requirements, although regulations are effective only if supported by rigorous controls. Since the intro- duction in 1990 of EU regulations controlling wines production (Martin, 1990; Zhang, Fourel, Naulet, & Martin, 1992), Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance (SNIF- NMR) has been recognized as the official method for detecting wine chaptalization (the addition of sucrose to the fermenting must to increase the alcoholic content of the wine), a type of wine fraud that may be resorted to in years when the grape harvest is poor. SNIF-NMR analysis is based on site-specific measures of D/H values in the methyl and methylene positions of ethanol [(D/H) I and (D/ H) II ]. As reported by Martin, Akoka, and Maryvonne (2006), the isotope ratio of the methylic site, (D/H) I , reflects the origin of car- bohydrate precursors in terms of plant species and, to a lesser extent, plant water (fermentation medium), whereas the methy- lene isotope ratio, (D/H) II , is mainly dependent on the D/H of the fermentation medium. The natural ranges of isotope ratios in ethanol obtained by fermenting different plant sugars, such as grape, beet and cane, are reported in Table 1 . When investigating chaptalization using the SNIF-NMR method, attention is normally focussed on (D/H) I , which yields ranges of values for wine which differ significantly from those of cane and beet sugars (Table 1). As reported by Bauer-Christoph, Wachter, Christoph, Roßmann, and Adam (1997), (D/H) II also can be useful for identifying the illicit adulteration of wine with cheaper ethanol. In fact (D/H) II is usually higher than 125 ppm in fruit or wine eth- anols (see Table 1), due to deuterium enrichment in fruit water (Rossmann et al., 1999), while ethanols from cereals, potatoes and sugar normally have lower (D/H) II values. These products are nor- mally made by mixing the raw materials with tap water before fermentation: tap water contains less deuterium than plant water as a consequence of evapotranspiration processes in plants (Rossmann et al., 1999). Two other important isotope ratios which can be used to detect chapatalization are 13 C/ 12 C (expressed as d 13 C) and 18 O/ 16 O(d 18 O) of ethanol, which are measured using Isotope Ratio Mass Spectrom- etry (IRMS). It is possible with the former to determine whether the ethanol in a grape derives from sugars from C4 plants, such as cane or maize. As reported in Table 1 , differences in photosynthesis mean that C3 plants (Calvin photosynthetic pathway), such as grapevine, contain less 13 C than C4 plants (Hatch-Slack pathway), such as corn or sugar cane (Farquhar, Ehleringer, & Hubick, 1989). Furthermore, * Corresponding author. Tel.: þ39 0461 615261; fax: þ39 0461 615288. E-mail address: matteo.perini@fmach.it (M. Perini). Contents lists available at ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont 0956-7135/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodcont.2013.12.015 Food Control 40 (2014) 368e373