Comparison of remediation strategies for decreasing ‘reductive’ characters in Shiraz wines

Abstract

Background and Aims: Winemakers utilise various remediation strategies for decreasing 'reductive' characters in wine. Remediation strategies, such as the addition of diammonium phosphate (DAP) during fermentation, copper fining, the addition of fresh lees or lees products to wine, and aeration of the must during and after fermentation, are commonly employed in an effort to prevent the formation or to remove undesirable volatile sulfur compounds. In this study, the relative effectiveness of five strategies for remediation of 'reductive' aroma was compared in a Shiraz wine. Methods and Results: At the onset of the development of 'reductive' aromas during Shiraz fermentation, each ferment was treated with a unique remediation strategy: DAP addition; macro-oxygenation; copper fining; a combination of macrooxygenation and copper fining; or the addition of fresh lees from a donor wine. While a relatively small difference in volatile sulfur compounds was found between treatments, copper fining, lees and DAP addition produced wines with elevated 'reductive' characters at certain time-points post-bottling; while macro-oxygenation or macro-oxygenation with copper produced wines with a low sensory score for 'reduction'-related attributes. Conclusions: Macro-oxygenation during fermentation was the most effective remediation strategy. Lees addition, and to a lesser extent, copper fining and DAP addition, diminished fruit attributes and produced wines with noticeable 'reductive' characters. Significance of the Study: Macro-oxygenation during fermentation produced wines with the lowest 'reduction'-related attributes while enhancing 'fruity' attributes. This work also highlighted the compositional effects of each type of remediation treatment.

Aeration ofVitis viniferaShiraz fermentation and its effect on wine chemical composition and sensory attributes

“…In Trial 1, however, H 2 S concentration in Control wines (T1_NT) was high [11 μg/L (Table S2)] and aeration during fermentation resulted in a substantial decrease in its concentration to a level comparable to the other three trials. This suppression of H 2 S observed in Trial 1 is consistent with previous observations (Bekker et al 2016, 2021). Overall, the data presented in this work suggest that when H 2 S concentration is already low, aeration has limited capacity to further decrease it.…”

“…In addition, aeration has been shown to increase metabolic flux through acyl‐CoA (Saerens et al 2006), a metabolite pool that may limit ester synthesis (Jouhten et al 2008) and might further contribute to the observed increases in short branched‐chain ethyl esters. Overall, our observations are broadly consistent with the existing reports that describe the impact of aeration on yeast‐derived volatile aroma compounds in red wine (Bekker et al 2016, 2021, Picariello et al 2020).…”

“…The effect of oxygen exposure on Shiraz sensory properties was consistent with other reports (Bekker et al 2016, 2021) and was demonstrated to enhance fruity nuances, decrease colour intensity, and lower astringent mouthfeel and bitterness in some cases. The enhanced fruit characters were consistently associated with an increase in ethyl‐2 and ethyl‐3 methylbutanoate, compounds recently shown to play dominant roles in red wine aroma (de‐la‐Fuente‐Blanco et al 2020).…”

“…In addition to the changes in volatile compounds typically associated with primary fruit characteristics in wine (Ugliano and Henschke 2009), a vintage‐specific suppression in the concentration of low molecular‐mass volatile sulfur compounds was also observed. The role of oxygen during red winemaking in diminishing the concentration of VSCs and their asociated reductive off‐odours is well documented (Gambuti et al 2013, Bekker et al 2016, 2021), and has been applied commercially (Brajkovic 2008). In three of the four vintages (Trials 2–4) described in this study, H 2 S concentration was already low in all Control wines (less than 2 μg/L) and was decreased minimally in aerated ferments.…”

“…Creation of study designs and sensory data acquisition was conducted using Fizz or Compusense Sensory software. Partial least squares regression (PLS‐R) was used to explore and model the relationships between wine composition and sensory data set and was conducted similarly to that described by Bekker et al (2021). Briefly, chemical variables ( x 's) and sensory responses ( y 's) were standardised, full cross‐validation was performed and NIPLAS algorithm was used with 30 000 iterations calculated.…”