The effects and research into smoke taint is only just being explored, but there are clearly a number of variables that have an impact on the damage smoke can do to vines.
THIS past vintage will be remembered for a long time. On-going drought, raging fires, smoke taint and finally the damage done to business by the Coronavirus have all created an anus horribilis. Not many regions escaped either the direct impact of fires or the smoke. According to the New South Wales Wine Industry’s Executive Officer, Angus Barnes, the Hunter, Mudgee and Hilltops regions has seen ‘around half’ of its production impacted by smoke. As one would expect, the worst affected regions were closer to the fire. They include the Shoalhaven Coast, Southern Highlands, Tumbarumba, Canberra District and Hastings River. Fortunately, the Riverina, Murray Darling, Perricoota and Swan Hill regions did not receive any damage, whilst Cowra and Orange recorded a low amount of taint. However, to put this all into perspective only 30,000 tonnes of grapes have been affected out of a NSW crush of 500,000 tonnes. The damage in Victoria was to the east, especially in parts of Gippsland and North East Victoria. In South Australia the fires caused havoc in the Adelaide Hills.
The effects and research into smoke taint is only just being explored, but there are clearly a number of variables that have an impact on the damage smoke can do to vines. The intensity and distance from the fire, the prevailing weather conditions and the duration of the event, will all have an impact on the concentration of smoke. The type of fuel that is being burnt can have an impact on the compounds in the smoke, some are worse than others. Then there is the topography of the vineyard area. “I know of one medium sized business that had to do around forty tests across their vineyards due to having different variables such as topography and grapes planted,” comments Angus.
Part of the Hunter Valley were severely affected by taint. The industry was taken by surprise when Bruce Tyrrell put out a press release in January saying that 80% of his Hunter production had been lost due to smoke taint. It seems that vineyards close to the Brokenback and Mount View Ranges were most affected, whilst those away from the hills, in say the Lovedale area, were less affected.
It was thought that the developmental stage that the grapes were in when exposed to smoke was important, but now doubt has been thrown into that thinking. Originally, the danger period was after veraison (when the grape colour changes and the berries begin to swell) right through to harvest. But in this season grapes have been affected pre-veraison as well.
Volatile phenols found in smoke do all the damage. These include Guaiacol, o-cresol, m-cresol, p-cresol, Syringol, 4 methyl-syringol and 4 methyl-guaiacol. They are converted to a bound form of the phenols called glycoside and once in the grape they are undetectable. Grape juice can be analysed for both free and bound phenols to predict the presence of smoke taint, but it is only when the juice is fermented that they come to the surface and is recognised as smoke taint with the aid of sensory evaluation. Grape growers have had to wait until close to ripeness to be able to get their juice and a micro ferment tested by one of only two laboratories in Australia that are set up to tackle the problem. Imagine the nervous wait of nurturing your grapes to maturity knowing that smoke from months ago might have already ruined a whole year’s work. Testing is done by a Gas Chromatography and results are measured in micrograms (UG) per kilograms. As a generalisation, below 25-50 UG is suggested to be ok, borderline is around 50 to 150 and anything above is rated in the high range of smoke taint, but this does depend on variables most notably the different grape varietals.
Some grape varieties are more susceptible to smoke taint than others. Thick-skinned varieties survive better, so pinot noir is more affected than say shiraz. Red grapes are affected more than white grapes, due to them spending more time in contact with their skins. It is thought that more smoke taint characters come out with bottle age.
In Victoria, there are trials underway of a smoke detection system that might solve the waiting game. Early detection is crucial. If this is successful then vignerons will save money on netting, pruning, spraying and harvesting what is already a damaged crop. Other research is looking at remedial action using activated carbon products and enzymes to use on infected grapes and wine. Whilst a third project in South Australia is looking at in-canopy misting to reduce the damage of smoke on grapes.
Some of the characteristics we see from smoke affected wines is a burnt or ashtray character, as well as aromas as varied as salami and disinfectant. Not surprisingly, there are some correlations between the flavours of charred wood of a toasted barrel and smoke taint.
So, what happens to ruined grapes? Well they aren’t picked. One producer I spoke to was buying more sheep to let them graze on the crop. Alternatively, you could try and make it into Brandy. Hartzview Vineyard dealt with the smoke taint from the devastating 2019 fires that ripped through the Huon Valley in Tasmania by putting their wine into a still.
The industry is working in unison to learn from this vintage says Barnes, “We have learnt a lot from the past and continue to work constantly with the NSW State Government, NWGIC (National Wine Grape Industry Centre at CSU) and the AWRI. Small batch fermentations of low, medium and high smoke taint wines are being made to catalogue and use in future research. In June this year, we will invite NSW wineries to submit samples of 2020 vintage wines so a panel of experts can assess them. The industry is resilient, there will be some great wines made in the 2020 vintage, which follows on from the excellent 2019 vintage and our message is to get out to the regions and support local wineries”.