Test developed to detect wine grapes exposed to forest fires

With summer quickly approaching and the temperature increasing, forest fires are a constant worry for wine producers and grape growers. Previous research has revealed that grapes on the vineyard can absorb and metabolise smoke from forest fires, leading to unpalatable wine. But the crucial issue is how to test if the grapes have been affected and how to manage their exposure to the smoke.

Rather than wait for the final product, researchers from the University of British Columbia (UBC) Okanagan have created an analytical test to measure the amount of volatile phenols — compounds absorbed by grapes when exposed to smoke that can impact wine flavour — that are present in the fruit before the wine is produced.

Zandberg worked with PhD student Matthew Noestheden and collaborated with several local vineyards and analytical company Supra Research and Development to produce the test. After reviewing scientific literature on how grapes absorb and metabolise the smoky-flavoured compounds, they used a series of chemical techniques to isolate the volatile phenols and precisely measure them.

Previously, winemakers had to wait about 10–14 days to detect the smoky compounds in grapes, “relying on subjective measures like taste and odour”, according to Wesley Zandberg, Assistant Professor of Chemistry at UBC. This long waiting time before finding out if fruit was suitable for wine production caused unnecessarily high costs. Some affected grapes were not detected until the finished wine was produced, and the longer the grapes stayed on the vine the more likely they were to be exposed.

“We’ve developed a test that detects the exact amount of volatile phenols present in the grape. There’s no need to ferment them first and we get results within a matter of hours,” said Zandberg.

He emphasised the importance of speeding up this process, stating, “By accurately and quickly measuring the presence of volatile phenols, we’re offering a much better tool to help vineyards and wineries manage the risk from smoke exposure. By knowing precisely whether and by how much each crop has been impacted by smoke exposure, growers and winemakers alike can make informed decisions about whether the grapes should be used or abandoned altogether.”

However, some wines are purposefully aged in smoked oak barrels that contain volatile phenols to produce smoky undertones. Zandberg was therefore careful to highlight that accurately measuring the presence of volatile phenols is not only useful in determining the suitability of the fruit before processing, but also in fermented grapes to balance the flavour of the finished wine.

“This could be hugely beneficial in helping winemakers determine whether wines have enough smoky compounds to match their desired flavour profile after ageing in smoked barrels.”

The study was published in the Journal of Agricultural and Food Chemistry and received funding from Mitacs, the Natural Science and Engineering Research Council and the British Columbia Grape Council.