While we might treasure cannabis terpenes, there are times and places where they may not be desirable. I know what you’re thinking. That’s hard to believe, right?
One such area where terpenes have not been desired is in the emissions from cannabis growhouses. Complaints from those who don’t appreciate the smell and regulations that govern such emissions have forced cannabis cultivators to implement effective ways to control/limit the aromas wafting out of the buildings.
Terpenes may also cause concern when cannabis or hemp farms are adjacent to other farms growing non-cannabis crops like grapes. Even if there is no credence to a specific worry, terpene drift may still provoke scrutiny from neighboring farmers. A recent study (not peer reviewed) evaluated the effects of hemp terpenes, if any, on wine grapes when the hemp was planted near the grape vines. [1] “There are concerns about hemp VOCs [volatile organic compounds] tainting other agricultural crops,” the researchers said, adding “in some regions of the US, some vineyard owners have reported fears regarding the impact that hemp terpenes may have on their wine grapes.”
Grape plants also contain terpenes/terpenoids that contribute to the sensory properties of their respective wines. These terpenes/terpenoids include linalool, geraniol, nerol, terpineol, and hotrienol, interestingly all terpene alcohols. The concentration of these terpenoids increases with increased maceration. [2] What’s more, researchers have found that different yeasts can create terpenoids like citronellol from geraniol or nerol, modifying the organoleptic properties. [3] Pretty solid stuff.
So, terpenoids in grapes are vital to the end product, just like cannabis. The question is, are the vineyards’ concerns warranted? Or, is this just another undeserved concern about cannabis cultivation?
There is credence that terpenes might drift onto neighboring crops. [4.5] Air and soil have been suspected delivery systems. The terpenes emitted from cannabis/hemp could float on air currents until they land on some other plant. Then, they could be assimilated by that plant. Thin leaves are more likely to take in the stray terpenes. [6]
Terpenes may also be absorbed by the roots of the neighboring plant. The terpenes can be released by microbes in the soil that decompose plants. The longer a plant is grown on a specific patch of land, the greater the contribution to the soil chemistry it has. In fact, soil can absorb terpenes released to the atmosphere, making this type of terpene drift more likely.
In the study [1], the hemp field contained two varieties (360 clones of Boax and 240 seedlings of Cherry Wine Boax) located 68.5 feet (20.9 meters) from the vineyard, which contained 39 types of grapes. Buffer crops of sunflower and corn were planted around the perimeter of the hemp field. Hemp plants were sampled each week for four weeks, from five weeks to one week before harvest. The samples were always collected between 8 and 9 AM. Hemp samples were transported to the lab within 30 minutes for analysis.
Grape samples were also collected, stored on ice, and transported to the lab. Finished wines were analyzed to see if the hemp terpenes blemished the wine. One group of wines was fermented with grape vine leaves to see if any terpenes absorbed by the leaves made it into the finished product. Several weather events (e.g., temperature, wind) were also studied since weather affects terpene drift.
Using headspace gas chromatography (HS-GC), hemp flowers, grapes, and wine samples were analyzed for terpene content. Interestingly, a sensory analysis was done by a human, because our olfactory system is suspected of being more sensitive to lower levels of some terpenes than are some analytical instruments.
The top three terpenes in the hemp were β-myrcene, β-caryophyllene, and α-ocimene. The levels of these terpenes spiked during the 3rd week of sample collection, so this period should impart the strongest effect on the wine grapes, were drift to occur. No hemp terpenes, however, were detected by HS-GC in the wine grapes during this period.
Ten wine tasters who were either winemakers or oenologists sampled the wines with our more sophisticated sense of smell. They were not informed about the point of the study, so they were not aware that hemp terpenes may have altered the wines. These test tasters found no signs of contamination from hemp terpenes.
The mandatory distance regulated by a local ordinance called for a minimum of 200 feet between hemp and a neighboring crop. This hemp field was placed just 68.5 feet away, and yet, the hemp did not change the chemistry of the grapes. The researchers point out that the corn or sunflower crops may have buffered terpene drift.
Wind analysis revealed many currents migrating from the hemp field right towards the vineyard. Other weather conditions were favorable for terpene drift, and yet neither machine nor human detected cross-contamination. While this paper may not be in a peer-reviewed journal, it provides a nice example of using science to test speculation.
References
[1] Sellu G, Kane M, Prendergast J, et al. Terpene drift from Cannabis sativa L. (hemp) and the implications for Vitis vinifera (wine grapes) planted in close proximity. Agriculture and Natural Resources Department at Santa Rosa Junior College.[2] Baron M, Průšová B, Tomášková L, et al. Terpene content of wine from the aromatic grape variety ‘Irsai Oliver’ (Vitis vinifera L.) depends on maceration time. Open Life Sciences. 2017;12:42-50. [journal impact factor = 0.69; times cited = 11 (Semantic Scholar)]
[3] Mateo JJ, Jiménez M. Monoterpenes in grape juice and wines. Journal of Chromatography A. 2000;881(1-2):557-67. [journal impact factor = 4.759; times cited = 376 (Semantic Scholar)]
[4] Sharkey TD, Yeh S. Isoprene emission from plants. Annu Rev Plant Physiol Plant Mol Biol. 2001;52:407-436. [journal impact factor = 26.379; times cited = 531 (Semantic Scholar)]
[5] Ormeño E, Fernandez C, Bousquet-Mélou A, Greff S, Morin E, Robles C, Vila B, Bonin G. Monoterpene and sesquiterpene emissions of three Mediterranean species through calcareous and siliceous soils in natural conditions. Atmospheric Environment. 2007;41:629-639. [journal impact factor = 4.798; times cited = 62 (Semantic Scholar)]
[6] Noe SM, Copolovici L, Niinemets U, Vaino E. Foliar limonene uptake scales positively with leaf lipid content: “non-emitting” species absorb and release monoterpenes [published correction appears in Plant Biol (Stuttg). 2008 Jul;10(4):527]. Plant Biol (Stuttg). 2008;10(1):129-137. [journal impact factor = 3.081; times cited = 37 (Semantic Scholar)]
Image Credit: eflon (Alex from Ithaca, NY), CC BY 2.0, via Wikimedia Commons
