Bushfire generated smoke taint in grapes and wine

Abstract

Grapevines exposed to smoke produce aromas in wine which can be offensive to consumers so it is important to the industry to have the means to measure and manage it. Losses can be massive as illustrated by figures from the Pemberton (WA) region showing grape and wine value cut by more than $7 million in 2004 due to unmarketable product.

Summary

Experiments over three seasons attempted to identify mechanisms of smoke assimilation, translocation and storage within organelles, with an emphasis on grape berries. Other enquiries concerned key periods of growth for negative effects to occur, sensory properties and isolation of volatile organic compounds in smoke. An important aim was to find vineyard-based amelioration techniques that would work. The project required devices for controlled exposure to smoke in the laboratory (using dry barley straw to reduce variation) as well as tents over field-grown vines.

Results included establishment of direct links between smoke exposure of field-based vines and subsequent development of smoke aromas. It was found that the peak of sensitivity to smoke began at seven days after veraison but the negative effects started to accrue as early as when berries were pea size. An important finding was that application of smoke to leaves alone gave high levels of smoke taint related compounds in the fruit. The duration or number of smoke exposures appears to be critical for the development of smoke taint in wine and repeated applications of smoke to grapevines result in increased accumulation of smoke compounds and aromas in wine. Furthermore, repeated applications result in the decline of grapevine leaf function and ripening capabilities of fruit.

Since the study suggests smoke compounds can be assimilated by leaves and translocated to the fruit, sampling may be a way of predicting the extent of problems. Another benefit to management is that critical periods have been identified.