Grape Smoke Exposure Effects: Determining the Compounds that Cause Smoke Impacts in Wine

The goal of this project is to determine the volatile chemicals in smoke that affect the flavor and aroma of wine and wine grapes for Pinot noir and Chardonnay. To differentiate chemicals derived from smoke from ambient grape or wine compounds, a fuel source, barley, was chemically “tagged” using 13CO2. As 13CO2 is assimilated by the barley, it is distributed throughout the plant and its chemical components, including the precursor smoke material, such as lignin. By identifying the major components from smoke, future studies may be able to better prevent off-flavors caused by smoke from nearby wildfires. More immediate conclusions may even begin to identify thresholds when crops are exposed to smoke to the point of sensory perception prior to harvest or fermentation.

To achieve these goals, in this year we have:

  • Implemented 13CO2 incubation cages for growing isotopically labelled barley (Figure 1)
  • Tested and concluded ideal practical conditions to maximize growth of 13C-labelled barley
  • Grew over 2 kg (dry weight!) 13C-labelled barley from January through September
  • Adjusted protocols to account for Covid-19 lockdowns and personnel distancing as outlined by state and university policies, continuing the project with minimal interruption
  • Begun processing and milling barley samples to determine lignin, carbohydrate, and dissolved composition through chemical methods, and 13C assimilation via isotope ratio mass spectrometry
  • Designed and constructed smokers and smoke tents for smoking wine grapes using chemically labelled barley as a fuel source (Figure 2)
  • Designed methodology to recreate high density smoke conditions while balancing cost[1]effectiveness of administering labelled smoke while ensuring the viability of the wine
  • Exposed over 20 kg Chardonnay and 20 kg Pinot noir grape clusters to labelled smoke, consistently holding smoke labelled smoke density >20 mg/m3 over the course of 3 days in October (Figure 3)
  • Made wine from grapes exposed to 13C-labelled smoke (Figures 4 and 5)

Preliminary aroma and flavor of smoke-exposed wine show a strong incorporation of chemicals associated heavily smoked grapes, with a marked difference between the grapes exposed to smoke in the tents and the control grapes that were exposed to smoke during the wildfire events in Oregon in September. Moreover, we expect to be able to differentiate the chemicals’ origins based on the NMR experiments and confirmed by GC- or LC-MS in 2021.