Sweet Red Wine Production: Effects of Fermentation Stages and Ultrasound Technology on Wine Characteristics

Three different sweet red wines were produced using Tempranillo grapes with three different sugar concentrations: 25, 50 and 75 g/L, using sulfur dioxide and low temperature to stop the alcoholic fermentation. They were compared to the wine produced without stopping the alcoholic fermentation. Cold pre-fermentation macerations and ultrasound during the post-fermentation stage were applied to try to improve the organoleptic properties specifically for sweet wines. The treatment with ultrasound after stopping the fermentation enhanced the extraction of anthocyanins compared to the wines produced without ultrasound, increasing the red color of the final wines, resulting in increments in the range of 16–30%. In any case, significant differences were found between the regular dry red wine and the sweet wines in terms of polyphenolic content, anthocyanin, tannin concentration and absorbance at 520 nm, with lower contents for the sweet wines. The wines were evaluated by different tasting panels showing different results depending on the tasting panel composition. First, an inverse relationship was observed between the sweetness of the wines and their acidity, bitterness, and astringency descriptors. Additionally, wines with higher sugar levels were described as having the most fruity aromas. Finally, no differences in vegetal aromas were found in the different wines.