Smoke is full of numerous different compounds, and there are at least 6 of these that can contribute to smoke taint in wine. The concentration of these compounds is logically higher in fresher smoke, so the danger is higher if you are closer to a fire, or if there is a strong wind to blow the smoke to you quickly. Also logically, the longer the smoke stays around, the higher the risk. We were over 60km from the nearest fire, but it did blow to us fairly quickly at times, and we had a few days of persistent smoke.
Grapevines don’t particularly like smoke, and unlike us, they can’t go inside and close all the doors and windows to escape it. So, their way of dealing with the toxicity is to bind the smoke compounds up so that they can’t freely move around the plant. These compounds can be quite high in the leaves, but the berries also absorb them, and store them mostly in the skin of the grape.
These bound up compounds actually have quite a high sensory threshold, so even if grapes contain fairly high levels of them, the grapes & juice can taste fine. It is the unbound or “free” volatile phenols which affect the aroma & taste of a wine – and unfortunately smoke tainted wine doesn’t taste reminiscent of a smokey whiskey, it’s more like used ashtray.
The bound compounds are quite stable, but some are released into their free form during fermentation, and the process continues slowly during the aging of the wine. This makes smoke taint quite difficult to deal with because if a wine tastes ok at any stage of the process (harvest, end of fermentation, bottling…), it doesn’t mean that it won’t develop a taint later on, and subsequently ruin barrels or be unpleasant after bottle aging.
Therefore, analytical testing is critical. We need to know how much of the bound form is there lurking behind the scenes so that we can make decisions. The tests are quite complex and can only be done in a specialised wine laboratory (there is only one in Victoria & one in South Australia). Each grape variety needs to be tested, because they vary in the amount of these compounds they absorb due to varietal differences as well as difference in grape ripeness levels at the time of smoke exposure.
Winemaking and wine style also affect the final level and/or perception of smoke taint. It is important to not get leaves mixed in with the grapes during harvesting, so careful hand harvesting is best (which is what we always do anyway). White wines have less skin contact during winemaking, so will extract less smoke compounds than reds which are fermented on skins. But then heavier more flavoursome wines (eg. full bodied reds) can have a higher threshold than lighter bodied wines, meaning they can get away with slightly higher levels.
So, there are no hard and fast guidelines for what is too much smoke. We have our first test results back (Shiraz), and although there is evidence of exposure to smoke, the test results are in the range where no-one can say whether the wine will show a taint or not. So, we are hopeful that with some careful winemaking (and a bit of good luck), we will still be able to make something good of it. But it will be a challenging vintage, and our focus will be to try and make the best decisions for our wines.
