Current smoke conditions are different from those observed in regions affected by smoke taint during 2003, 2007 and 2009. However it is still critical for producers to assess their risk of smoke taint in a structured and methodical manner.
The mechanism of smoke taint evolution is complicated and measuring risk should not be based solely on analysis of marker compounds at the grape stage. Harvesting, juice extraction, processing and fermentation all have a significant influence on the evolution of smoke taint. There may be a significant pool of potential precursor smoke taint compounds which can be liberated during these processing stages that will influence the final level (or absence) of taint.
The first step in assessing smoke taint risk if the smoke event occurs earlier than 2 -3 weeks before harvest (knowing many are already closer than this) is to conduct a small lot fermentation using the AWRI's protocol: http://www.awri.com.au/wp-content/uploads/small_lot_fermentation_method.pdf. The wine resulting from this mini- ferment can be subjected to sensory assessment and chemical analysis in order to gauge the potential risk of any smoke taint that might arise from the smoke exposure.
This mini-ferment approach will provide the best possible indication as to the likely risk of smoke taint as it is based on assessment of a finished wine made from the possibly affected grapes. When conducting the sensory assessment of the wines, be sure to look for all different sensory (aroma and taste) expressions of smoke taint: ashy aftertaste, vinyl aroma, medicinal, salami, bacon, dull or metallic characters (not to be confused with acidity or tannin) on the palate. A number of laboratories, including the AWRI, are able to analyse wines for smoke taint marker compounds: 'free' volatile phenols such as guaiacol, 4-methyl guaiacol, m-cresol, o-cresol, p-cresol, syringol, methyl syringol.
When a mini-ferment wine sample shows no sensory indication of smoke taint, it is still possible that while having little or no 'free' volatile phenols, it has large amounts of 'bound' forms present in the wine. Over time this 'bound' fraction will break down, via acid hydrolysis, into the 'free' volatile and aromatic forms. Therefore testing for 'bound' glycosides is a good means of assessing the overall risk of the wine to ensure it does not exhibit problems during wine maturation/ageing. A number of laboratories, including the AWRI, also offer an analysis which tests for the glycosidically 'bound' fraction.
Additional information about smoke taint and its management can be found on the AWRI website.
For queries about assessing smoke taint risk, sampling and testing of grapes, juice or wine please contact Mark Krstic or the AWRI winemaking services team.
Australian Wine Research Institute – Victorian Node
Mobile 0437 325 438
AWRI winemaking services team
Phone (08) 8313 6600