Evaluating Smoke Contaminants in Wine Using 13C-Labelled Barley as a Fuel Source

Abstract

Wildfires are becoming more common in many areas of the world that are also associated with wine grape production, especially the Pacific northwest United States, Australia and even some areas of France. Wine grapes have shown to be incredibly sensitive towards the smoke produced from nearby wildfires, acquiring negative sensory characteristics, such as ashy, burnt, or campfire-like flavors and aromas. The chemical markers often associated with smoke, guaiacol and 4-ethyl guaiacol, can delineate the presence of a nearby fire, though there has been some disagreement on the chemical components responsible for some of the negative flavors and aromas.1,2 This study uses a 13C-tagged fuel source, barley (Hordeum vulgare), that is grown in 13CO2 for 10 days of its life cycle using pulse-labelling techniques. 13C content of the barley was evaluated using isotope ratio mass spectrometry, revealing 13C/12C content as high as 4.47 ± 0.75% compared to the natural ~1.08% for natural abundance in plant material. Grapes were exposed to 13C-labelled smoke in separate post- and pre-harvest trials, burning 5 g and 10 g dried barley bundles, respectively, every 30 minutes for 6 hours. Smoke density was piped “cold” to enclosures containing wine grapes and smoke was maintained at 20-100 mg/m3 for smoke particles < 1 μm, simulating a very nearby fire. The exposed grapes were Pinot noir and Chardonnay grown in Monroe, Oregon at Woodhall III Vineyards. The 13C is ideal for chemical identification using 13C-NMR after HPLC and GCMS separation and evaluation to identify novel targets for smoke chemicals affecting wine. Determining better chemical targets for amelioration will ultimately lead toward better, more targeted, amelioration techniques.