Grape stems as preservative in Tempranillo wine

Abstract

SO2 is the most widely used preservative in the wine industry. However, there are several drawbacks related with the use of SO2 in wine such as its toxicity and the unpleasant odor in case of excess. These reasons justify the importance of searching alternatives to reduce or eliminate this preservative from wine. The grapes stems are discarded early on in the winemaking process, in spite of containing large amounts of polyphenolic compounds with antioxidant activity. The aim of this work was to determine whether the ground stem and its extract had the potential to replace SO2 in wine. For this, five Tempranillo red wines were made: a positive control with SO2 (60 mg/L); a negative control without any preservatives; a wine with Tempranillo stem extract (200 mg/L); a wine with a combination of Tempranillo stem extract (100 mg/L) and SO2 (20 mg/L), and a wine with ground Tempranillo stem (310 mg/L). After a year of bottle storage under cellar conditions, the wines with different treatments had similar values for antioxidant capacity (ABTS), total polyphenolic or total anthocyanin content. The most abundant individual polyphenols found in all samples were gallic and caftaric acids, catechin and malvidin-3-glucoside. The evolution of all these compounds throughout the winemaking process followed the literature. Positive control wine had a higher concentration of caftaric acid. The concentrations of gallic acid, catechin and malvidin-3-glucoside were more homogenous among treatments. The sensory analysis by a triangular test showed that the positive control wine was only perceptibly different from the Tempranillo extract wine and the negative control at 99% confidence level. Tempranillo stem wine only differed from the wine that combined SO2 and extract. Negative control wine differed from all treatments, except Tempranillo stem. This may indicate both the Tempranillo extract and ground stem may be good total or partial substitutes for SO2 as an antioxidant in red wines.