If a smoke event has occurred
Sampling, sending and testing of grapes
If a smoke event has occurred, an option is to have samples tested for the presence of the smoke-related marker compounds such as guaiacol, 4-methylguaiacol, cresols and syringols.
Samples can include wine grape berries, grape juice, leaves and wine. Testing of grapes and juice can indicate whether the fruit has been exposed to smoke. Low levels of these compounds can be naturally present in fruit, with levels elevated after smoke exposure.
Guaiacol and 4-methylguaiacol detection in fruit cannot be used as a determinant of the smoke-effect intensity in the final wine, as this is influenced by fruit handling and processing. If you are concerned that grapes may have been affected by smoke, sampling is best done as close to harvest as possible. Testing may be ineffective on grapes sampled earlier.
Testing laboratories may interpret test results however ‘bench-top’ or ‘small-lot’ fermentation of grapes prior to harvest is suggested to provide indication of smoke-effect intensity in the final wines. Research is ongoing to determine more effective analysis of grapes for the presence of smoke-related characters.
When taking samples, collection of fruit and vine material should be done early in the day prior to high temperatures and vine stress. Samples should be taken across the entire vineyard area and be collected randomly. Samples should be kept cool, and frozen if to be posted interstate.
Plant Health Certificates to facilitate quarantine requirements for movement of grapevine material interstate are often required and can be obtained from the relevant State Departments of Agriculture/Primary Industry. For instance, a Plant Health Certificate is required for movement of plant material from WA to eastern Australia and can be obtained from Quarantine WA by phoning +61 (0)8 9334 1800.
Some laboratories offer testing for the presence of smoke-related compounds in grapevine samples. Many are in eastern Australia and include The Australian Wine Research Institute, phone +61 (0)8 8313 6600 and Vintessential Laboratories, phone 1300 30 2242.
Additional laboratories may analyse smoke-related compounds in plants and these services vary in location, cost and type. In cases of extreme smoke exposure of an entire region, a central collection point is often organised by the state government to move material for testing interstate.
Techniques to reduce smoke taint
After smoke exposure of field-grown grapevines, a number of techniques can be employed in both the vineyard and winery to reduce the concentration of smoke-related aromas, flavours and compounds in the final wine.
Many are detailed in the following table and are more effective when used in combination rather than alone.
|Hand harvest fruit||Minimise breaking or rupturing of skins as long as possible1,2|
|Exclude leaf material||Leaf material can contribute smoke-related characteristics when in contact with fruit and juice1,2|
|Wash grapevines||Canopy leaf plucking followed by high-pressure cold water wash in the vineyard can remove ash7, however washing the entire canopy (including leaves) can accentuate smoke compounds in fruit8|
|Maintain structure of harvested fruit||Fruit maceration and skin contact with juice can lead to higher concentrations of smoke-related compounds2|
|Keep fruit cool||Fruit processed at 10°C had less extraction of smoke-related compounds than fruit processed at 25°C1,2|
|Whole bunch press||This has been shown to reduce extraction of smoke-derived compounds particularly in whites1,3|
|Separate press fractions||Smoke characters could be minimised in the first 400 L/t when combined with fruit cooling. Free-run juice can contain fewer smoke characters1,2,3|
|Conduct fining trials before fermentation||Carbon, PVPP and isinglass have shown variable effectiveness in reducing smoke characteristics but are not selective. Fermentation management requires further consideration after fining1,2,3|
|Consider yeast selection||Some yeast strains can alter smoke-related aromas, flavours and chemical composition of wine4|
|Minimise fermentation time on skins||Fermentation that reduces skin contact time can reduce smoke aromas and flavours1,4,5|
|Consider addition of oak chips and tannin||Oak chips can reduce intensity of smoke characteristics through increased wine complexity4|
|Reverse osmosis of wine||Reverse osmosis can be effective in smoke reduction, however taint was found to return in the wine over time6|
|Market wine for quick sale||Smoke-related characteristics can evolve in bottle as wine ages1,3,6|
1Simos 2008, 2Whiting and Krstic 2007, 3Ulrich 2009, 4Ristic 2011, 5Kennison et al. 2008, 6Fudge et al. 2011, 7Høj et al. 2003, 8Kennison 2009.
Management of fire-damaged vines
During a fire, grapevines may be physically damaged by flames and/or by radiant heat from the fire. Often both the physical damage and radiant heat damage may appear similar and range from slight scorching of leaves to complete destruction of the vine.
Fire may damage all grapevine structures and result in injury or death of leaves, leaf petioles, buds on canes and shoots (including latent buds), flowering and fruit production organelles and the vascular system.
Depending on the degree of damage, vines may recover to full fruit production or be irrevocably damaged and die.
At any given vineyard site, fire damage is often inconsistent and highly variable. Weather conditions, fire ferocity and the growth stage can all contribute to the degree of vine damage. A limited number of investigations of grapevines following fire have focused on assessing the immediate damage and applying pruning treatments.
Useful techniques for assessment of grapevines after fire damage include:
- Visual vine assessment: To be conducted immediately after the fire and include assessing damage that may be ‘nil’ (no visible damage), ‘low’ (such as minor leaf scorch), ‘medium’ (damage to leaves, inflorescence/fruit) or ‘high’ (severe scorching and damage to all plant parts from contact with flames). Visual assessment should be based on individual varieties and record the location of vine damage within a block.
- Cambium assessment: A small knife incision in the trunk can be made to investigate the colour of the cambium tissue. Healthy tissue is moist and green, damaged tissue is dry and pale, while dead tissue is dry and brown (Whiting 2011).
- Trunk staining: This was investigated by Scarlett et al. (2011) where transect sections of trunk are cut and stained with methylene blue. If the segment is bright blue then the tissue is ‘viable’, if the trunk segment is a dirty blue or brown then the tissue is ‘unviable’. This method is destructive to the vines, however provides an immediate indication of the fire’s effect.
- Bud dissection: Can provide indication of viability and potential fruitfulness of buds within cane material. With a microscope, dissection of buds indicates whether they are alive (green) or dead (brown/black). Dissection is best conducted prior to winter pruning in order to provide information on the optimal number of buds to retain on the vine and their position within the canopy.
After comprehensive assessment of grapevines after fire damage, a number of management techniques can be employed to aid recovery. Techniques depend on the severity of damage that includes:
- No damage: Continue vine management as usual, paying attention to grapevine health. Apply additional irrigation to vines that show heat stress symptoms from the fire.
- Low damage: Continue vine management as usual, applying additional irrigation after the fire. Consider a pruning strategy to investigate (bud dissection) and retain viable buds during vine dormancy.
- Medium damage: Apply irrigation as soon as possible after fire. Monitor vines for stress and further signs of decline, and investigate health status of cambium material in trunks. Investigate bud fruitfulness prior to dormant pruning as additional buds may need to be retained to encourage growth and fruitfulness. Vine fruitfulness may be impacted in the following season and additional training of replacement vine shoots, arising from the crown and cordon, may be required.
- High damage: Likelihood of survival is low. Vines should be irrigated to encourage recovery, however destructive methods of survival assessment (trunk staining) would provide an immediate indication of viability. Vines may be minimally pruned to encourage shoot growth in viable buds and further assessed for survival in the following season. Replanting or grafting of unproductive vines may be required.
Applying irrigation is a common treatment however may be difficult if irrigation lines have been damaged from the fire.
Fudge, AL, Ristic, R, Wollan, D & Wilkinson, KL 2011, Amelioration of smoke taint in wine by reverse osmosis and solid phase adsorption. Australian Journal of Grape and Wine Research 17(2), S41‑S48.
Høj, P, Pretorius, I & Blair, R (eds) 2003, The Australian Wine Research Institute Annual Report 2003. (The Australian Wine Research Institute, Adelaide, Australia) pp.37‑39.
Kennison, KR 2009, Bushfire generated smoke taint in grapes and wine. Final report to Grape and Wine Research and Development Corporation, RD 05/02‑3.
Kennison, KR, Gibberd, MR, Pollnitz, AP & Wilkinson, KL 2008, Smoke-derived taint in wine: the release of smoke-derived volatile phenols during fermentation of Merlot juice following grapevine exposure to smoke. Journal of Agricultural and Food Chemistry 56, 7379‑83.
Ristic, R, Osidacz, P, Pinchbeck, KA, Hayasaka, Y, Fudge, AL & Wilkinson, KL 2011, The effect of winemaking techniques on the intensity of smoke taint in wine. Australian Journal of Grape and Wine Research 17(2), S29‑S40.
Scarlett, N, Needs, S & Downey, MO 2011, Assessing vineyard variability after bushfire. The Australian and New Zealand Grapegrower and Winemaker 564, January 21‑25.
Simos, C 2008, The implications of smoke taint and management practices. Australian Viticulture Jan/Feb 77‑80.
Ulrich, T 2009, When the smoke cleared: California winemakers face tough pre-bottling decisions for 2008 wines. Wines and Vines July 46‑52.
Whiting, J 2011, Grapevine recovery from fire damage. Poster abstract in Proceedings of the 14th Australian Wine Industry Technical Conference, Adelaide, 3‑8 July 2010, R Blair, T Lee, S Pretorius (eds).
Whiting, J & Krstic, M 2007, Understanding the sensitivity to timing and management options to mitigate the negative impacts of bush fire smoke on grape and wine quality – scoping study. Department of Primary Industries, Knoxfield, Victoria.