 IVES 9 IVES Conference Series 9 Shades of shading: chemical and sensory evaluation of riesling grown under various shading techniques

Shades of shading: chemical and sensory evaluation of riesling grown under various shading techniques

Abstract

AIM: Sun exposure is needed for balanced grape ripening and sugar accumulation but is also one of the main drivers for a premature Riesling ageing. The aim of this study was to evaluate the modulation of both intensity and quality of light in the vineyard on key Riesling grape and wine parameters as an adaptation strategy to changing climate. Of particular interest was the kerosene aroma caused by the C13‑norisoprenoid TDN and other compounds associated with light-induced grape compositional changes.

METHODS: Over two vintages shade cloth of three different colours was applied to Riesling vines at bunch zone in South Australia. Light measurements and incident light wavelength assessments were performed during grape ripening, and subsequent grapes and wine were analysed for key bound and free aroma compounds. After 1-year of storage, wines were analysed by Quantitative Descriptive Analysis to quantify the holistic changes of light modulation to the sensory profile.

RESULTS: Depending on colour, shade cloth was successful in modulating either the quantity and/or wavelength of light, as well as showed different response of sugar accumulation. Shading reduced TDN concentrations and kerosene aroma in wines, with very little effect on other sensory descriptors. Interestingly, while presumed C13-norisoprenoid precursor profiles were altered between shading treatments, no significant differences were observed in resulting TDN levels.

CONCLUSIONS

This study highlights the importance of light intensity over examined light wavelength in the vineyard to manipulate TDN. Additionally, light conditions differently affected maturity with possible implications for harvest timing and climate-induced vintage compression.

DOI:

Publication date: September 13, 2021

Issue: Macrowine 2021

Type: Article

Authors

Yevgeniya Grebneva

The Australian Wine Research Institute & the Department of Microbiology and Biochemistry, Hochschule Geisenheim University,Markus, HERDERICH, The Australian Wine Research Institute, Adelaide 5064, Australia Doris, RAUHUT, Department of Microbiology and Biochemistry, Hochschule Geisenheim University Eleanor, BILOGREVIC, The Australian Wine Research Institute, Adelaide 5064, Australia Josh, HIXSON, The Australian Wine Research Institute, Adelaide 5064, Australia

Contact the author

Keywords

riesling, norisoprenoid, tdn, shade cloth

Citation

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The impact of Saccharomyces yeasts on wine varietal aroma, wine aging and wine longevity

The objective of the present work is to assess yeast effects on the development of wine varietal aroma throughout aging and on wine longevity.

Three independent experiments were carried out; two fermenting semi-synthetic musts fortified with polyphenols and aroma precursors extracted from Tempranillo (1) or Albariño (2) grapes and with synthetic precursors of polyfunctional mercaptans (PFMs), and a third in which a must, mixture of 6 different grape varieties was used. In all cases, fermentations were carried out by different Saccharomyces cerevisiae strains and one S. kudriavzevii, and the obtained wines were further submitted to anoxic accelerated aging to reproduce bottle aging. The volatile profile of the wines was analyzed using several chromatographic procedures, in order to provide a comprehensive evaluation of wine aroma. Aroma compounds analyzed included fermentation volatile metabolites, grape-derived aroma compounds including PFMs, and Strecker aldehydes (SA).

Results revealed that the effects of yeast on wine aroma throughout its self-life extend along three main axes:

1. A direct or indirect action on primary varietal aroma and on its evolution during wine
aging.

2. The direct production of SA during fermentation and/or their delayed formation by producing the required reagents (amino acids + dicarbonyls) for Strecker degradation
during anoxic aging.

3. Producing acids (leucidic, branched acids) precursors to fruity esters. More specifically, and leaving aside the infrequent de novo formation, the action of the different strains of yeast on primary varietal aroma takes four different forms:

1.- Speeding the hydrolysis of aroma precursors, which leads to early aroma formation without changing the amount of aroma formed. In the case of labile molecules, such as linalool, the enhancement of young wine aroma implies a short-living wine. 2.- Metabolizing the aroma precursor, reducing the amounts of aroma formed, which can be of advantage for negative aroma compounds, such as TDN or guaiacol; 3.- Transforming grape components into aroma precursors, increasing the amounts of aroma formed, as for ethyl cinnamate, leucidic acid or vinylphenols; 4.- Forming reactive species such as vinylphenols able to destroy varietal polyfunctional mercaptans.

Overall, it can be concluded that the yeast carrying alcoholic fermentation not only influences fermentative wine aroma but also affects to the wine varietal aroma, to its evolution during aging and to the development of oxidative off-odors

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