The effectiveness of a postveraison application of the film-forming antitranspirant Vapor Gard® (VG, a.i. di-1-p-menthene) was investigated as a technique to delay grape ripening and reduce sugar accumulation in the berry. The study was carried out over the 2010–2011 seasons in a non-irrigated vineyard of cv. Sangiovese in central Italy. VG was applied at 2% concentration to the upper two-thirds of the canopy (most functional leaves) and it significantly lowered leaf assimilation and transpiration rates and increased intrinsic water use efficiency. The Fv/Fm ratio was not modified emphasizing that photoinhibition did not occur at the PSII complex, whereas the reduction of pool size of plastoquinone matched well with reduced CO2 fixation found in VG-treated vines. In both years VG treatment reduced both the pace of sugar accumulation in the berry as compared to control vines, scoring a −1.2 Brix at harvest and wine alcohol content at −1% without compromising the recovery of concentrations of carbohydrates and total nitrogen in canes and roots. Concurrently, organic acids, pH and phenolic richness of grapes and wines were unaffected, whereas a lowering in anthocyanin content in the berry (−19% compared to control vines) and in the wine (−15% compared to control vines) were found. The application of VG at post-veraison above the cluster zone is an effective and easy-to-do viable technique to hinder berry sugaring and obtain less alcoholic wines. To be effective it is advised to perform the spraying at around 14–15 Brix making sure that the lower leaf epidermis is fully wetted by the chemical.