Smoke taint

The tainting of grapes and wine by bushfire smoke is an industry problem, highlighted by several fire events over the past decade.

Guaiacol and 4-methylguaiacol have been identified as important compounds attributed to ‘smoky’ taint in juice and wine as a result of bushfire smoke. Recent research outcomes at the AWRI have shown that other volatile phenols such as cresols and syringols can also contribute to smoke taint characters.

The AWRI Commercial Services has an inexpensive and rapid method to measure these compounds accurately in grapes, juice and wine to levels less than the sensory threshold. Results will enable wineries and growers to make informed decisions about the risk of smoke effects impacting on the wine. The analysis of volatile phenols includes determination of the following compounds:

Guaiacol 4-methylguaiacol syringol methylsyringol
m-cresol o-cresol p-cresol

Sensory studies at the AWRI have shown that the sensory threshold for guaiacol in white wine is approximately 6 μg/L and between 15 and 25 μg/L in red wine.

The most effective time to test levels of these volatile phenols in grapes is as close to the harvest date as possible. It should be noted, however, that reporting of low concentrations of these volatile phenols in grapes at harvest is not a guarantee that any wine made from those grapes will be free from smoke taint. Some volatile phenols have the potential to be released during fermentation as a result of the presence of their glycoside precursors. In response to issues associated with the release of bound forms of volatile phenols, such as guaiacol, we recommend conducting laboratory-scale ferments in an attempt to understand better the actual impact on the final wine. This will provide an indication of potential levels of volatile phenols likely to be liberated from the precursor forms.

Research continues to characterise these precursors and their impacts and to develop diagnostic or predictive assays to quantify the potential for release of volatile phenols during fermentation. Analysis of glycoside precursor compounds in grapes, juice and wine is available and includes determination of six glycoside conjugates shown to be significant with regard to smoke-effect. The glycoside conjugates determined in the analysis are:

Guaiacol-rutinoside 4-methylguaiacol Syringol-gentiobioside
Cresol-rutinoside Phenol-rutinoside Methylsyringol-gentiobioside
Prices per analysis
Analysis Sample type Cost (ex GST)
Volatile phenols + non-volatile precursors wine $247
Volatile phenols + non-volatile precursors grapes $295
Volume required – 500 g berries OR 100 mL wine

For more information, please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au.

Data interpretation and winemaking advice

Results from analysis of both the volatile phenols and glycoside precursors can be compared with baseline data to assist with determining potential risk of smoke effect.

For assistance with data interpretation and winemaking advice to reduce the potential effects from smoke-related phenols, please contact the AWRI helpdesk on (08) 8313 6600 or e-mail helpdesk@awri.com.au.

Further information can be obtained from the AWRI website: Smoke taint Smoke taint analysis FAQ Small-lot fermentation method