 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

The colour pattern of flower arrangements influence wine tasters’ sensory description

The arrangements of flowers and wine counterparts are inextricably linked. Whether a fundamental aspect of tablescaping or acolytes to broader entertainment rituals, they have an entangled history since ancient times. The aim of this contribution is to verify the influence of visually delicate and robust flower arrangements on individual description of wines. Changes in the sensory description of wines were investigated during subjects’ (thirty-two participants) exposure to three different conditions: the presence of delicate, robust, or totally absent flower arrangements. In each condition, the same two wines were blind tasted: a wine previously defined as delicate – a Pinot Noir from Australia, and a wine known for its robust character – a Tannat from Uruguay.

Early defoliation positively enhances bioactive composition of berries with no effect on cuticle characteristics

Leaf removal in the fruit-zone has been employed to improve cluster light exposure and ventilation and therefore increase metabolite accumulation and reduce botrytis incidence in berries. When applied before flowering (early defoliation – ED), it can also decrease cluster compactness and regulate yield in high-yielding varieties. This study aimed to evaluate the impact of ED on the physiology and metabolism of Aragonez (syn. Tempranillo) berries along the ripening period. The experiment was set up in 2013 at a commercial vineyard located in the Lisbon winegrowing region.

Physical-mechanical berry skin traits as powerful indicators of resistance to botrytis bunch rot

The ongoing climate change results in increasing mean air temperature, which is manifested by weather extremes or sudden changes between drought and local heavy rainfalls. These changing conditions are especially challenging for the established grapevine varieties growing under cool climate conditions due to an increased biotic infection pressure. Thus, the scope of most grapevine breeding programs is the selection of mildew fungus-resistant and climatic adapted grapevines with balanced, healthy yield and outstanding wine quality. Since no resistances or candidate genes have yet been described for Botrytis bunch rot (BBR), physical-mechanical traits like berry size and thick, impermeable berry cuticles phenotyped with high-throughput sensors represent novel effective parameters to predict BBR.

Towards understanding the mechanisms of resistance to grapevine Flavescence dorée

Flavescence dorée (FD) is a very serious grapevine disease, classified as quarantine in europe, where it appeared in the middle of the last century. It is associated with the presence of phytoplasmas, transmitted in the vineyard by a leafhopper of american origin, scaphoideus titanus. FD causes severe wine production losses and often leads to plant death. There are currently no alternative solutions to insecticide treatments against the vector and uprooting diseased vines.

Publication of the 3rd edition of the OIV ampelographic descriptors

Ampelography is aimed at describing the vine according to several characteristics, such as morphology, agronomic aptitudes, technological potential, and genetics. The description of varieties and species of vitis has long been the subject of numerous scientific and technical studies by eminent specialists for a long time, which have led the OIV to publish in 1983 the “descriptor list for grape varieties and vitis species”, a milestone among the OIV worldwide recognised codes.