Effects of Dehydration Treatment on the Quality of Sweet Wine from Hetianhong Grapes at Different Ripeness Levels

This study systematically evaluated the effects of dehydration treatment (water loss level of 15%, 30%, and 45%) and grape maturity (20 and 24 °Brix) on the quality of sweet white wines produced from Hetianhong, a native table grape variety in Xinjiang that is currently underutilized in deep processing. Dehydration increased the total sugar and total acid concentrations in grape must while also significantly elevating the alcohol content, total acidity, total reducing phenolic equivalents, DPPH radical-scavenging activity, and total volatile flavor compound content in the resulting wines. Specifically, the total volatile content in group A3 was 5.93 times that of the non-dehydrated control group A0, which was prepared from the same raw material. Notably, dehydration promoted the formation of 3-hydroxy-2-butanone, a compound that contributes creamy, nutty, and roasted notes to the wines’ profile. Furthermore, dehydration significantly elevated the concentrations of aldehydes and ketones, and higher alcohols, with the aldehyde/ketone content in group A3 being 8398.11 times that of A0, and in group B3 being 10,787.98 times that of B0. Conversely, dehydration led to a significant reduction in the levels of volatile fatty acids, The impact on volatile phenols is not significant. Dehydration alters the distribution of acetates: ethyl acetate levels increase in the dehydration group, whereas isopentyl acetate levels decrease as the degree of dehydration increases. Sensory evaluation revealed that dehydration enhanced the fruity, rosy, and creamy attributes of the wine. Moreover, grape maturity significantly increased the total reducing phenolic equivalents (B0 was 2.96 times that of A0), the DPPH radical-scavenging activity, and the total content of volatile flavor compounds, including the individual contents of higher alcohols, acetate esters, volatile fatty acids, and terpenes. In addition, PCA and OPLS–DA effectively differentiated dehydrated from non-dehydrated wines. A total of 27 key volatile compounds were identified (OAV > 1), 10 of which had VIP > 1. Notably, eight volatile compounds, including (Z)-3-hexenyl acetate, 3-hydroxy-2-butanone, isoamyl lactate, ethyl isovalerate, n-propanol, isoamyl alcohol, ethyl acetate, and isobutanol, were more abundant in groups A1, A2, and B1. This study provides a theoretical and technical foundation for the processing of the Xinjiang table grape variety Hetianhong.