Macrowine 2021
IVES 9 IVES Conference Series 9 Measuring elemental sulfur in grape juice in relation to varietal thiol formation in Sauvignon blanc wines.

Measuring elemental sulfur in grape juice in relation to varietal thiol formation in Sauvignon blanc wines.

Abstract

Aim: Sauvignon blanc displays a range of styles that can include prominent tropical and passionfruit aromas. Both sensory evaluation and chemical analysis have confirmed the above-average presence of ‘varietal thiols’ in the Sauvignon blanc wines from Marlborough, New Zealand.1 The varietal thiols are released from cleavage of non-volatile sulfur-containing precursors or an interaction between a sulfur donor and a C6-compound.2 Machine-harvesting is the most common harvesting practice used in New Zealand, by which, there is a higher probability to add some leaves to the must. Leaves and grapes can contain elemental sulfur (S0), which is commonly sprayed in the fields to protect berries against powdery mildew. S0 is known to cause unwanted reductive aromas, including H2S, in certain wines unless remediation steps are undertaken during winemaking. Also, it was shown that extra S0 addition to the crushed grapes could lead to more varietal thiol formation in wines.3 Despite the clear effects of residual S0 present in the must on the final wine quality and aroma4, its measurement is not a regular practice undertaken in wineries due to the lack of easy and applicable methods.

Methods: We have optimized a sulfide sensor for S0 measurement in grape juice samples and investigated the correlation between S0 concentration in grape juice and varietal thiols concentration in final wines. A simple apparatus was designed to reduce S0 to sulfide using dithiothreitol (under acidic conditions, as H2S), followed by an ion-selective electrode (ISE) to measure sulfide concentrations (under alkaline conditions as S2-). GC-MS is being used to analyze thiol concentrations in wine samples to allow comparisons to be made with juice S0 concentrations.

Results: The semi-log calibration curve plotted based on the ISE data showed very good linearity. The results also showed that the reduction process was successful, and the apparatus is working well with both standard and juice samples. The ISE was confirmed to be able to detect the reduced sulfur at concentrations as low as 0.01 ppm.

Conclusion

The methodology allows action between the concentration of S0 residues and the concentration of varietal thiols in the final wines to be investigated. The analysis is applicable in a winery setting to evaluate the potential of grape juices to form varietal thiols and/or reductive compounds in wines

DOI:

Publication date: September 7, 2021

Issue: Macrowine 2021

Type: Article

Authors

Bahareh Sarmadi

School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand,Paul A. Kilmartin, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand Brandt P. Bastow, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand

Contact the author

Keywords

Sauvignon blanc, elemental sulfur, varietal thiols

Citation

Related articles…

Methodology of climate modelling using land surface temperature downscaling: case study case of Gironde (France)

Aim: Climate modelling in viticulture introduced new challenges such as high spatio-temporal monitoring and the use of dependable time series and robustness modelling methods. Land surface temperature (LST) is widely used and particularly MODIS thermal satellite images due to their high temporal resolution (four images per day).

A first look at the aromatic profile of “Monferace” wines

Grignolino, is a native Piedmont grape variety which well represents the historical and
enological identity of Monferrato, a territory between Asti and Casale Monferrato, included in the World Heritage List designated by UNESCO (1).

Sviluppo di una metodologia di tracciabilità e definizione dell’impronta petrochimica in suoli e vini della Sicilia occidentale nella piana di Marsala (TP)

I risultati delle ricerche condotte in un vigneto sperimentale di Marsala (TP), scelto per omogeneità di fattori bio-agronomici (età, tecniche colturali, potenzialità vegetativa e produttiva)

IMPACT OF MANNOPROTEIN N-GLYCOSYL PHOSPHORYLATION AND BRANCHING ON WINE POLYPHENOL INTERACTIONS WITH YEAST CELL WALLS

Yeast cell walls (CWs) may adsorb wine components with a significant impact on wine quality. When dealing with red wines, this adsorption is mainly related to physicochemical interactions between wine polyphenols and cell wall mannoproteins. However, mannoproteins are a heterogeneous family of complex peptidoglycans including long and highly branched N-linked oligosaccharides and short linear O-linked oligosaccharides, resulting in a huge structural diversity.

Beyond classical statistics – data fusion coupled with pattern recognition

AIM: Patterns in data obtained from wine chemical and sensory evaluations are difficult to infer using classical statistics.