Memstar News : Dealing with smoke tainted grapes and wine – Don’t panic!
Posted by Anonymous on 21/02/11 (4046 reads)

The recent fires in and around Victoria have thrown vintage plans into chaos. Now that the immediate fire danger has passed, many growers and winemakers are disturbed by the risk of smoke taint. Timely harvest decisions are being delayed while grapes are analysed and in many cases, fruit is being rejected on the basis of fear and poor information.

The economic damage as a result is severe and widespread. It may also be avoidable.

Since 2003, our understanding of the smoke taint phenomenon has grown considerably. While it is far from complete, valuable research has been done and techniques have been developed to minimise the effects on the wine. The first and most important thing is – Don’t panic!

In this regard, the decision to delay or cancel the harvest of grapes is the most damaging and it is irrevocable. It may be the most pragmatic option but it should not be made in haste, or based on incorrect or obsolete information. There are some important facts that are relevant:

• Guaiacol (G) and 4-methylguaiacol (4MG) measurements in grapes may be misleading. These compounds are useful indicators but the levels in grapes and juice are not reliable predictors of the ultimate taint in the final wine. They may be the tip of an iceberg. The problem is we can’t really tell how big or dangerous the rest of the iceberg is at this early stage. Different varieties and winemaking practices can have a significant effect on the taint extraction rates.

• Most G and 4MG are not in the free form - In grapes and juice, guaiacol and 4-methylguaiacol appear to be substantially in the bound, glycosidic form. They do not fully appear in the detectable, free form until after fermentation and even then there is some ongoing release for a few months. This is dependent on residual sugars and the extent of glycosidase enzyme activity.

• Treating grape juice is of limited benefit - The other implication of this is that any benefits from trying to remove the taint compounds at the juice stage may be limited and short-lived. In the past, massive amounts of activated carbon have been used to treat juice. Generally the result has been that the wine is stripped of almost all desirable flavours while leaving the volatile phenols to emerge after fermentation.

• Be patient – Nothing much can be done until after fermentation and clarification of the wine. Only then will the extent of the problem be clear and then treatment is possible and effective.

• Smoke affected wines can be recovered - Contrary to some popular gossip, it is possible to successfully reduce the taint in affected wine. Memstar started working on a reverse osmosis and adsorption process in 2003 and considerable development has taken place since then. This is now a viable and effective treatment for smoke affected wines, with almost a millions litres from 2007 vintage successfully treated.

For example, in 2007 a Yarra Valley Pinot Noir was treated and analysed. The results are about to be published in a GWRDC report. In summary:




Table: Effect of membrane filtration and solid phase adsorption treatment on the concentration of smoke derived volatile phenols in Pinot Noir wine (Source: Wilkinson, KL, Amelioration of Smoke Derived Taint in Wine by Membrane Filtration and Solid Phase Adsorption, Final Report To
Grape and Wine Research & Development Corporation, Not yet published)

The treated wine was bottled and has been successfully marketed with no negative feedback from the market.

Let us help - Memstar will do whatever it can to assist affected Victorian growers and winemakers get over this crisis:

• No obligation trials - We have lab scale equipment to do no-obligation, no-charge trial treatments of affected wines. We can get a meaningful indication on as little as 5 litres of wine.

• On site or at Memstar - This service is available as soon as there are wines ready for assessment. We welcome a reasonable number of samples from winemakers with affected wines.

• All options considered - If winemakers are prepared to harvest their grapes and make wine, we will look at all reasonable options for reducing and sharing their risk and potential loss.

As a matter of urgency, we would welcome the chance to meet with individuals or groups of growers and winemakers to explain the issues and propose some approaches so that the harm is minimised.

Please contact Memstar (1300 636 782) or directly - David Wollan (0414 948 184, dwollan@memstar.com.au ) or Gary Baldwin (0418 172 142, gbaldwin@winenet.com.au)

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