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Standardisation, validation and publication of the acid hydrolysis approach for analysis of smoke-exposed grapes and wine across multiple laboratories to support surge capacity during bushfire events

Summary

Objective

The purpose of this study is to support the availability and surge capacity of analysis capability and provide evidence for the sector that there is reliability in the GC-MS method for measurement of bound phenols in smoke-affected grapes and wines. Specifically, the acid hydrolysis method will be standardised across the GC-MS machines at three Winechek laboratories (Barossa Valley in SA, Margaret River in WA and Yarra Valley in Victoria) and the results will be validated against the research laboratory at La Trobe University, where the method has been performed routinely for several years, to optimise the method for both the WineChek and research laboratories.

Once the testing method is refined and validated, Winechek will seek NATA accreditation for its provision as well as publishing details of the technique and its performance characteristics. Publication of acid hydrolysis as a repeatable and scientifically robust method will promote acceptance and trust of the method as a diagnostic test for smoke taint and support adoption and routine use more widely.

Background

Smoke taint is a risk for grape and wine businesses in many areas of Australia and will only increase under climate change conditions. The bushfires of 2020 highlighted a number of deficiencies in the measurement of risk of smoke damage to grapes and wine in Australia. Only two commercial laboratories were able to conduct the analysis, and demand for testing resulted in a backlog of samples which sometimes forced grape growers and wine producers to make harvest decisions before receiving results. Growers also experienced transport and logistical challenges in moving grapes between states to the two testing facilities, and the analysis is expensive for users of the service.

In addition, the labs use different methods to determine the levels of smoke markers in grapes and wine. Both laboratories use gas chromatography (GC-MS) to analyse the free compounds. For measurement of bound compounds, Vintessential Laboratories (now Winechek) uses an acid hydrolysis step and then measures a set of seven released free volatiles by GC-MS[1]. This method is also used in the research lab at La Trobe University by Prof Ian Porter and his team. The AWRI (now Affinity Laboratories) uses liquid chromatography (LC-MS)[2] to analyse a group of six bound compounds directly as glycosides, without the hydrolysis step. GC-MS and LC-MS provide very different values, contributing to confusion among grape growers and winemakers on how to interpret the results. Several comparison studies[3] have highlighted differences between laboratories and demonstrated that results from the methods cannot be directly compared, but both are legitimate methods that can contribute to decisions on smoke exposure. This project is not an attempt to compare the GC-MS and LC-MS methods.

Since 2020, AWRI Commercial Services began trading as Affinity Labs and Vintessential Laboratories was acquired by Winechek, which consolidated labs at five regional locations in the Barossa Valley, Yarra Valley, Mornington Peninsula, Orange, Margaret River and Tasmania. Winechek has invested in two GC-MS machines located in South Australia and Western Australia and replaced the original unit in Victoria. This will expand the availability and surge capacity of analysis capability to a regional-based service at three locations across Australia, with the intention to eventually provide a results interpretation as part of the service. This co-investment will deliver the ability to deliver accurate and reliable results will reinforce confidence in the analytical method and the risk-based assessment models developed using this method, which support decision making by grapegrowers and winemakers managing smoke exposed fruit.

Sector benefits

This work will improve smoke taint diagnostics for Australian wine producers. Increasing the number of labs nationally from two to four, via Winechek’s regional model, will improve surge capacity for grape testing in a major bushfire event and reduce sample transport issues. Provision of a reliable and standardised method for analysing smoke-impacted grapes and wine will improve confidence in the results and the interpretation, enabling Australian winemakers and grapegrowers to make informed decisions about their level of risk after smoke exposure. Better management will in turn lead to better outcomes and ensure production of high-quality wines even under challenging conditions.


[1] Allen, D., A. D. Bui, N. Cain, G. Rose and M. Downey (2013). Analysis of free and bound phenolics in wine and grapes by GC–MS after automated SPE. Analytical and Bioanalytical Chemistry 405(30): 9869-9877.

[2] Hayasaka, Y., Baldock, G. A., Parker, M., Pardon, K. H., Black, C. A., Herderich, M. J., Jeffery, D. W. (2010). Glycosylation of smoke-derived volatile phenols in grapes as a consequence of grapevine exposure to bushfire smoke. J. Agric. Food Chem. 58(20): 10989−10998.

[3] Favell, J.W.; Wilkinson, K.L.; Zigg, I.; Lyons, S.M.; Ristic, R.; Puglisi, C.J.; Wilkes, E.; Taylor, R.; Kelly, D.; Howell, G.; et al. Correlating Sensory Assessment of Smoke-Tainted Wines with Inter-Laboratory Study Consensus Values for Volatile Phenols. Molecules 2022, 27, 4892. https://doi.org/10.3390/molecules27154892

Wilkinson, K., Ristic, R., Pinchbeck, K., Fudge, A., Singh, D., Pitt, K., Downey, M., Baldock, G., Hayasaka, Y., Parker, M., Herderich, M. 2011. Comparison of methods for the analysis of smoke related phenols and their conjugates in grapes and wine. Aust. J. Grape Wine Res. 17(2): S22-S28.

Wilkes, E. and Howell, G. (2020) Cross-validation of 2020 grape and wine smoke analytical data between Vintessential and AWRI Commercial Services laboratories. https://www.awri.com.au/wp-content/uploads/2020/12/Smoke-analysis-cross-validation-report-FINAL-30-Nov-2020.pdf

Schmidtke, L. (2020). AWRI and Vintessential Grape and Wine Analysis Smoke Method Comparison. https://www.vintessential.com.au/smoke-taint-test/

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This content is restricted to wine exporters and levy-payers. Some reports are available for purchase to non-levy payers/exporters.