Dr. George Sellu, Ph.D. Scientifically Assesses the Danger of Grape Taint from Hemp

By Laurie Wachter

In 2019, the Santa Rosa Junior College initiated a hemp cultivation project at Shone Farm to specifically identify the best agronomic practices for cultivating hemp and understand the potential terpene drift between hemp and wine grape vines.

“Since launching Wine and Weed Symposium,” WIN President and CEO George Christie says, “I’m often asked a question I couldn’t find anyone to answer until I met Dr. George Sellu. ‘Will hemp terpenes negatively influence grapes if grown too close to a vineyard?'”

“A lot of people are concerned about whether hemp will taint wine grapes,” agrees Sellu, Santa Rosa Junior College’s (SRJC) Agribusiness Program Coordinator/Instructor, “but I couldn’t find any research in the US to support that concern.” So, he implemented a study to measure drift from hemp acreage into vineyards at SRJC’s Shone Farm. The conclusion: no hemp terpenes were detected on wine grapes or in wine made from those grapes, either by instruments or a wine sensory panel. Drift from spraying vineyards has a higher chance of negatively impacting hemp since far fewer products are approved for hemp than for grapes. Christie points out that this could open grape growers to liability.

Sellu suspects that some may not understand the plant terpenes responsible for aromas and flavors. Two examples, linalool in lavender and pinene in raspberries, carrots and pine trees, are both in hemp and grapes. “If you find pinene in wine grapes,” he says, “you wouldn’t blame someone growing carrots nearby.”

Christie noted that San Luis Obispo banned hemp in Edna Valley, citing grape taint and crime concerns. “There’s not enough THC in hemp to get high,” Sellu responds. “Why would anyone steal it? Colorado planted thousands of hemp acres and have yet to see any theft. If farmers can’t make money from their acreage, they’re going to move away. You might get $30 an acre for corn or wheat, and $1000 an acre with hemp – that’s the difference between making money and losing your farm.”

Sellu promises to expand his research to other wine regions. Then he offers some advice. “Plant hemp for fiber instead of CBD oil. CBD oil prices fell 50% last year because too many acres were planted. Demand for CBD will fade, while fiber will be here for a long time. Businesses are switching from products like Styrofoam to hemp fiber, which is more sustainable. Georgia Pacific uses it to make Brawny paper towels and Levi’s and Patagonia for pants. Others use it for flooring, car parts or sails. Even though you’ll earn less per acre than for CBD, fiber is the longer-term play.”

Download: Dr. George Sellu’s Powerpoint Presentation (PDF)

Follow-Up Q&A from the Live Broadcast Chat

Q: “Can this hemp study be applied to the effects of growing marijuana strains that are grown for medical/recreational purposes? If not, would it have to do with the differences in terpene content?”

A: “Certainly! CBD Hemp varieties are similar to Marijuana in terms of structure and terpene production. The terpene profile will differ based on the variety of hemp or Marijuana.”

Q: “If there is a terpene transfer from hemp to wine grapes, did you look at the stage of wine grape ripeness relative to development of terpene development in hemp?”

A: “Terpene production in hemp increases as the plant approaches flowering and peeks about a month before harvest (for full term hemp varieties). We planted our hemp late so that flowering coincided with fruit ripening in grapes. We harvested the grapes two weeks before the hemp. As you saw from my presentation, terpene production in hemp was declining at the end of data collection.”

Q: “Could the terpenes in hemp and cannabis behave differently?”

A: “We have did not explore that question. Generally, specific terpenes in CBD hemp and Marijuana should have the same chemical properties. The terpene profile will differ based on the variety and the levels of individual terpenes. Fiber hemp generally has lower levels of terpenes compared to CBD varieties.”

Q: “What was the limit of quantification for the terpene method? Terpenes are present in ppb levels. Commercial labs only analyze to PPM level.”

A: “The limit on quantification for terpenes in commercial labs is PPM. I am not sure if our local commercial wine labs have developed methods for quantitating hemp terpenes in wines.”

Q: “Many times, Eucalyptus can be tasted in a wine produced from vineyards surrounded by Eucalyptus trees. The wine is often describe as having ‘mint’ tones. What are your thoughts regarding different terpene sources?”

A: “Minty taste is associated with eucalyptol. Some researchers have found eucalyptol in grapes that are not planted in close proximity to eucalyptus. They have suggested that eucalyptol in wine is also produced by transformation during the winemaking process.”

Q: “Are you saving wine samples for future analysis and tasting?”

A: “Yes, we are saving these wine samples for future testing and analysis.”

Q: “I have talked with some help producers and they have had to post signs that “Hemp will NOT get you high” to avoid theft. Did you have any issues with theft at the Shone Farm? If so, how did you address. Asking as other community colleges have raised this question if growing hemp on student farms.”

A: “We had no problem with theft. We had very clear signage all around the field and we installed cameras.”

Q: “Can future research also consider proximity of drying/processing cannabinoid species to vineyards? I have been hearing there is potential concentration of terpenes during the drying/processing process.”

A: “We have not thought about drying close to our field. That could be an interesting study. We would have to do a early hemp variety because wine grapes are harvested before hemp.”

Q: “Actually, anecdotally, in SBC (Santa Barbara County) we have vintners complaining about the cannabis flavor influencing the wines. Also, we have grows proposed up to 80 acres down here. That’s going to have a significantly bigger impact than 1/3 acre of hemp, the test size.”

A: “Thanks for your comment. We do not know that the size of the field makes a difference. We were looking at proximity to the vineyard. If the County you’re in has an ordinance that stipulates an easement between hemp and vineyards based on research then this will address some of the litigations going on in SBC. This would also give UC Cooperative Extension some time to conduct larger studies.”

Q: “The Right to Farm was not applied to cannabis because you a) cannot tax a crop, so that is how a County makes money on cannabis, and b) The Right to Farm protects odor and odor is a significant problem for hemp and cannabis.”

A: “Absolutely agree with you. The right to farm protects farmers from the odor concerns. I think it will be hard for Counties to shutdown hemp cultivation primarily based on odor concerns.”

Q: “Thank you for this research and conversation. Are there any grape growers that are transitioning or making room to grow hemp? It sounds like it could be a healthy sign for grape growers as hemp is held to a higher standard than conventionally grown wine grapes.”

A: “I think there are a lot of grape growers who are considering diversifying their farming to include crops such as hemp because of the current drop in grape prices across the US.”

Dr. George Sellu, Ph.D.
Program Coordinator, Instructor, Agribusiness / Santa Rosa Junior College

George Sellu joined the SRJC Agriculture and Natural Resources faculty in Fall 2013. George received a Bachelor of Science in Agriculture and Environmental Science with an emphasis in Soil Science from the University of Sierra Leone and a MS and PhD in Agricultural Science/Education from the University of California, Davis. George has 10 years of experience teaching high school agriculture courses in California. In addition to high school teaching, George taught at Woodland Community College for three years prior joining SRJC faculty. George’s vision is to guide students develop effective business skills that address community and industry needs.

In addition to teaching, George is very interested in international agricultural development and food security in sub-Saharan Africa. Currently, he consults for Non-Governmental Organizations (NGOs) that are funded by the World Bank and the United States Agency for International Development (USAID).

He is an active member of the California Agricultural Teachers’ Association (CATA), American Association of Agricultural Educators (AAAE) and the American Educational Research Association (AERA).