Alternative Technologies to Modify and Measure Red Wine Astringency and Quality

Abstract

Astringency is an important mouthfeel factor driving wine quality, complexity and consumer preferences. Wine astringency is mainly perceived due to the interactions between polyphenols in wine and salivary proteins during consumption. The wine industry has invested heavily in the analysis of wine phenolic composition and its effects on flavour/mouthfeel. However, our understanding regarding the relationships between specific phenolic fractions/compounds and their respective astringent mouthfeel and sub-qualities (e.g. grippy, puckering), as well as novel and improved techniques for measuring astringency perception and modification of wine astringency levels, are still limited. This thesis comprises a number of studies to investigate these research gaps. The findings of these studies are contained within the thesis chapters two through to and inclusive of chapter five. These are presented here as two published, peer-reviewed papers, one submitted manuscript and one unsubmitted work written in a short research communication format following the introductory chapter one and are outlined in the following summary. Firstly, in an attempt to improve methods to examine human astringency perception and elucidate the different yet more subtle astringent sub-qualities caused by different chemical parameters (basic wine composition and phenolic profiles), a modified progressive profiling was explored. Dynamic astringency profiles of 13 Australian commercial red wines and 2 roses made from 1 1 grape varieties were generated using a trained, modified progressive profiling sensory panel. Overall astringency intensity and 6 sub-qualities: pucker, mouth coat, dry, grippy, adhesive and graininess defined by the panel were rated at six time periods (lasting 10 seconds each), with 20 second gaps between each period. Wine composition and phenolic profiles were also determined to establish correlations with mouthfeel attributes. This alternative sensory methodology enabled dynamic and quantitative intensity measurement of astringent attributes, providing enhanced understanding of the chemical basis of subtle wine astringent sub-quality differences. Secondly, due to consumer demand for non-animal-derived processing aids, the efficacy of potato proteins to manipulate astringent compounds in red wine and the steps required for its optimisation of fining were investigated. This represented the first study to examine the potato protein dose-response kinetics of tannin and phenolic compound removal for two unfined Cabernet Sauvignon wines. Testing the influence of wine matrix and fining parameters (including pH, ethanol concentration, sugar concentration, temperature, and agitation) were according to a fractional 25- 1 factorial design. Insights into potato proteins' optimal use revealed that fining efficiency could be increased by treating wines at higher than usual cellar temperatures (20 °C), and at both a lower pH and/or alcohol concentration. Thirdly, an investigation of a new grape-must polyphenol extraction technique: Accentuated-Cut-Edges (ACE) revealed its capacity for modifying wine astringency. This study reported the effect of the ACE technique on non-volatile chemical composition of Shiraz wine (basic wine chemistry, colour, phenolic components and polysaccharides) and sensory profiles (using rate-all-that-apply and modified progressive profiling) for the first time. Furthermore, any potential improvement provided by ACE for the pre-fermentation water addition to must to reduce alcohol was investigated. The ACE technique increased the intensities of adhesiveness and graininess, which partly overcame the impact of water addition on the astringent sensation. Fourthly, as the experimental Shiraz wines for the ACE study were produced in smallscale fermentation batches (25kg), an investigation at the industrial scale was warranted. Therefore, two pilot commercial wines (ACE with 5-day skin contact and NOACE with 8 days on skins) were produced in 2018 by the Corio le winery at industry scale (averaged 2.45 tonnes for each treatment) and were chemically analysed and underwent sensory profiling in 2019 alongside the ACE research wines in Chapter four. It was a preliminary experiment investigating the feasibility of ACE grape must extraction technique on Shiraz wines at an industry scale. This study indicated that ACE could potentially be used by the wine industry to combat one of the challenges of climate change, vintage compression, caused by climate change, by pressing wine ferments earlier, freeing up tank space for other wines. In conclusion, the research contained in this thesis provides advanced insights and alternative tools for researchers and the wine industry. Uncovering what components impact wine astringency, knowing how to better evaluate perceived wine astringency along with its sub-qualities and modify this important wine sensory attribute with a more informed approach, will enhance the capability of wine producers to better cope with some of the ramifications of climate change such as higher alcohol levels and vintage compression, target product style and quality plus meet consumer expectations.