Amending high sugar in V. vinifera cv. Shiraz wine must by pre-fermentation water treatments results in subtle sensory differences for naïve wine consumers

Abstract

Global warming presents challenges to all wine-grape growers and winemakers across the globe. Increasing growing season temperatures means that grapes are harvested with higher sugar concentrations than preferred for high-quality winemaking. The now Australian permitted water-treatment of high-sugar musts can produce wines with lower alcohol levels, however, recent studies show impacts on associated chemical compounds and sensory parameters can affect final wine quality. Commercial applications based on these earlier findings are limited as many focus on one vintage, one or two harvest timings, small wine samples and limited numbers of panellists for sensory analysis. We expand by first investigating the chemical profiles and sensory parameters of wines produced from V. vinifera cv. Shiraz for three harvest times: early 13.5°Baumé (°Bé), middle 14.5 °Bé and late 15.5 °Bé across two vintages (2020/2021). Just-About-Right sensory analysis assesses 159 naïve wine consumer panellists’ feedback. We show late 15.5 °Bé and middle 14.5 °Bé wine has the highest levels for chemical compounds of colour density (a.u.), total tannin (%), total pigment (a.u.), total phenolics (a.u.) and free anthocyanins (mg/L), as confirmed by PCA analysis outcomes. Sensory analysis shows the least preference for vegetal smell (2.50) in 13.5 °Bé wine, with the highest preference for colour intensity (3.06) in early 13.5 °Bé wine and body in late 15.5 °Bé wine. Secondly, 15.5 °Bé and middle 14.5 °Bé pre-fermentation musts are subject to water dilution or ‘bleed and replace’ treatments. These wines have lower final alcohol levels, decreases in most chemical compound levels, but with subtler effects for sensory profiles. For instance, there is a high preference for astringency (3.01), ripe fruit taste (2.96) and hotness (2.95) in late diluted 13.5 °Bé wine. Vegetal smell (2.89) is most preferred in late ‘bleed and replace’ 13.5 °Bé wine. All water treatments have minimal impact on dark fruit smell, ripe fruit smell, odour intensity, odour complexity, red fruit taste and dark fruit taste. Middle diluted 13.5 °Bé wine has the highest overall rating and is the most preferred. This study offers valuable insights revealing that water treatments of pre-fermentation musts can produce wines with preferable lower alcohol levels, and while this winemaking approach may negatively affect several chemical compounds, many favourable sensory properties can still be preserved. This is a crucial consideration for winemakers when addressing wine quality from these winemaking techniques.