By Elizabeth Higley and Kevin Elder, Windsor Run Cellars
Screening North Carolina Wine Grapes for Potential Pesticide Residue and Ochratoxin-A
Summary
Two wines were screened (an early season white and late season red) for potential pesticide residue as well as Ochratoxin-A after primary fermentation and again after sterile filtration (0.45 micron) to determine if residues were present, would the winemaking process reduce the amount.
Both white and red wines came back post-fermentation with residue levels well below the US EPA tolerance levels for the detected compounds. Both wines also had well below the EU regulated limit (2 ug/L) for Ochratoxin-A.
Post-sterile filtration, both wine samples came back with pesticide residues similar or slightly lower than the pre-filtration samples and Ochratoxin-A tested the same as the post-fermentation samples.
Introduction
Growing grapes on the east coast of the United States presents intense and unique challenges as it relates to disease pressure compared to other winegrowing regions. In North Carolina and the rest of the southeastern US, we often see an unprecedented amount of rainfall and humidity that unfortunately, demands a much higher frequency of chemical control to keep the vines and fruit healthy and free of disease. On average, most commercial growers are applying chemical control anywhere from 20-30 times per growing season, which could be considered high when compared to other growing regions.
Additionally, in years where disease pressure is high, and grapes come in compromised from the vineyard with disease present on the clusters, we could potentially be more at risk of having Ochratoxin-A present in our wines.
Ochratoxins (OT’s) are mycotoxins found in wines. Ochratoxin contamination occurs when grapes are still on the vine, during the ripening period when fungal infections are more active. Aspergillus carbonarius, A. ochraceus, A. niger, Penicillium verrucosum, and P. nordicum are the main fungal species responsible for producing this toxin in grapes, with Aspergillus species being more frequent (1). The National Library of Medicine also states that Ochratoxins should raise a tremendous public health alert worldwide for frequent drinkers, since these toxins can cause acute to chronic poisoning (1).
Due to the high frequency of chemical control and potential disease present in North Carolina, we wanted to know if our finished wines have any alarming amounts of pesticide residue or Ochratoxin-A, and if so, will the residue be removed through the standard winemaking processes like racking and ultimately, final filtration.
Methods
Two wines were selected to be screened for pesticide residue and Ochratoxin-A. Wine #1 was an early season white, 2023 Seyval Blanc harvested on August 23rd and wine #2 was a late season red, 2023 Cabernet Sauvignon harvested on November 3rd. Both wines were made using standard winemaking procedures and the first round of samples were sent to ETS for analysis following the completion of primary fermentation.
The Seyval Blanc was aged in stainless steel. Following stabilization and filtration, the wine was bottled in March 2024. The final sample was taken from the bottle, post-0.45 micron sterile filtration and sent to ETS.
The Cabernet Sauvignon was pressed, put through MLF and barreled down in December 2023. The final sample was pulled from the barrel in May 2024 and sterile filtered in the lab on a benchtop filter to 0.45 micron, then sent to ETS.
The Pest II Multiresidue Screen as performed by DFA identifies the presence of a variety of carbamate and GC/MS/MS pesticide residues following an acetone extraction. Approximately 300 possible pesticides may be identified by searches against 2 spectral libraries.
Results
It should also be noted that the 2023 vintage was above average in quality, with less overall precipitation and disease pressure. Majority of the fruit received came in exceptionally clean and the vineyard manager was able to back down significantly on chemical control as harvest approached. This screening should be performed again, especially in more challenging growing seasons so that we can better understand the implications of heavy chemical applications as well as high incidence of diseased fruit on our final wines.
References
Ortiz-Villeda, Bryan et al. “Ochratoxins in Wines: A Review of Their Occurrence in the Last Decade, Toxicity, and Exposure Risk in Humans.” Toxins vol. 13,7 478. 10 Jul. 2021, doi:10.3390/toxins13070478
