Mitigation of climate change impacts on the national wine industry by reduction in losses from controlled burns and wildfires and improvement in public land management
This is a collaborative project with partners including Wine Australia, the Australian Government Department of Agriculture and Water Resources, Agriculture Victoria, La Trobe University, Wine Victoria and the AWRI. The AWRI’s role is to evaluate a range of possible remedial management options and processing tools for dealing with smoke-affected grapes and wine. This is especially important as smoke taint is known to develop during bottle ageing of wine through continued conversion of non-volatile glycosides from contaminated grapes into their free volatile forms. In addition, the AWRI is collaborating with Agriculture Victoria/La Trobe to evaluate vineyard-based monitoring, preventative and remedial management options for dealing with the variable composition of atmospheric smoke and associated risk of smoke taint in wine.
This project is supported by Wine Australia, through funding from the Australian Government Department of Agriculture and Water Resources as part of its Rural R&D for Profit program and the Australian Wine Research Institute.
Smoke taint mitigation studies
Sensory dilution studies
A low to moderately smoke-affected 2016 Pinot Noir wine was diluted with unaffected Pinot Noir of a similar style, sourced from the same vintage and state, to investigate the practicality of using dilution to diminish or eliminate the sensory impact of smoke taint. The dilution series included no dilution (100% smoke-affected wine), dilutions of 1 in 2 (50% smoke-affected wine), 1 in 4 (25% smoke-affected wine), 1 in 8 (12.5% smoke-affected wine) and 1 in 16 (6.25% smoke affected wine). The unaffected Pinot Noir was also evaluated unadulterated (0% smoke-affected wine). A sensory panel rated ‘smoke’ aroma, ‘smoke’ flavour, ‘overall fruit’ aroma and ‘overall fruit’ flavour. Results showed significant differences (p<0.05 or lower) among wines for fruit and smoke-related attributes. Dilutions of smoke-affected wine with 75% or more unaffected wine resulted in smoke aroma and flavour scores not significantly different from the unaffected wine. When considering the concentrations of smoke glycosides, diluting the smoke-affected wine by a factor of four or more reduced their concentrations to what is typical of baseline levels for a Pinot Noir wine. This study highlighted that dilution of smoke-affected wine by an unaffected wine is a feasible option to diminish the sensory impact of smoke taint. However, this study was performed on a low to moderately smoke-tainted wine and additional studies will be needed to see if this result is more broadly applicable to different wines with varying levels of smoke taint.
Fourteen types of activated carbon were investigated for their effectiveness in fining smoke-affected wine and juice. Carbon products that were more effective at removing smoke glycosides than free smoke volatiles were identified and the influence of contact time and the presence of ethanol versus sugar was investigated. Carbon was less effective at removing smoke glycosides and volatile phenols in red wine than in juice and preliminary investigations suggest this may be due to pigments and tannins in the wine rather than ethanol. Investigations are underway to characterise differences in the activated carbon products which may explain differences in their removal efficiencies (e.g. surface characteristics such as zeta potential). Studies to date have been largely limited to red juice and wine due to the limited availability of smoke-affected white juice and wine; however, with the latter now having been sourced, additional studies will commence shortly.
The ability of six commercially available glycosidase enzymes to cleave smoke glycosides in smoke-affected juice and wine was investigated under various temperatures, contact times and dosage levels. In Pinot Noir wine, all glycosidases effectively cleaved the gentiobiosides; however, there was no subsequent increase in free smoke volatile phenols, a result which requires further exploration. The elevated sugar levels in juice inhibit the action of the glycosidases, so their use is best suited to wines that have completed fermentation. Glycosidase experiments on smoke-affected Cabernet Sauvignon wines from the USA have commenced. Future studies will focus on the sensory impact of glycosidase treatment and whether this is a viable option for reducing smoke taint in wine, or whether it needs to be combined with other treatments such as fining with activated carbon.
Sourcing smoke-affected juice and wine
Fortunately for industry there were very few incidents of smoke affecting Australian vineyards in 2017; however, this meant that obtaining smoke-affected grape and wine samples for mitigation and sensory studies was a challenge. In February 2018, NSW experienced a bushfire caused by a storm event, resulting in several vineyards being affected by smoke. This provided the opportunity to source smoke-affected fruit (Sauvignon Blanc, Chardonnay, Riesling, Pinot Noir) for the project. Two smoke-affected blocks (Chardonnay and Pinot Noir) were surveyed to investigate the variation of levels of smoke taint compounds in fruit sampled across the vineyard. Smoke-affected juice from Riesling, Sauvignon Blanc and two clones of Chardonnay was sourced and two wines (Sauvignon Blanc and Pinot Noir) were produced from smoke-affected fruit. In addition, smoke-affected Cabernet Sauvignon wines were sourced from California. Smoke-affected juice and wine samples will be used in mitigation and sensory studies.
The AWRI’s survey of baseline concentrations of volatile phenols and phenolic glycosides in non-smoke-exposed grapes and wines was completed at the end of 2017. The ‘background survey database’ now includes data for 12 varieties from more than 500 grape samples acquired from 23 regions across Australia. The database contains background levels for the white varieties Chardonnay, Pinot Gris/Grigio, Riesling, Sauvignon Blanc and Semillon, and the red varieties Cabernet Sauvignon, Grenache, Mataro/Mourvèdre, Merlot, Pinot Noir, Sangiovese and Shiraz.
The database is used by AWRI helpdesk staff to aid with interpretation of the results of AWRI Commercial Services’ Smoke Taint Panel analysis. Interpretation involves comparing the Smoke Taint Panel results with those from the background survey database for the particular variety analysed.
AWRI staff visited NSW in February 2018 to present an information and sensory evaluation session on smoke taint in response to a regional bushfire event. There has also been regular contact with wineries in California affected by bushfire smoke to provide technical expertise and diagnostic support, and to access smoke-affected wines. The AWRI has supported Wine Victoria, the Victorian Department of Environment, Land, Water and Planning and growers who were likely to be affected by smoke from planned burns to discuss management options.