December 20, 2024
3 minimum read
What gives a Christmas tree a refreshing and pleasant aroma?
Learn which molecules give Christmas trees their distinctive crisp, spicy aroma
Yulia Bondar/Getty Images
Nothing smells better than a Christmas tree. But where does that magical, woody yet comforting scent come from? You can thank a ubiquitous category of chemicals called terpenes.
“Terpenes are the largest class of naturally occurring chemicals in the world,” says Justin Whitehill, a plant pathologist who studies Christmas trees full-time at North Carolina State University. “They are found in almost every plant species.”
Terpenes can play a wide range of ecologically beneficial roles. They can protect plants from hungry predators and parasites, attract pollinators, and help plants tolerate stressful conditions. The specific terpenes produced, as well as the purposes they serve and the aromas they produce, vary by species.
About supporting science journalism
If you enjoyed this article, please consider supporting our award-winning journalism. Currently subscribing. By subscribing, you help ensure future generations of influential stories about the discoveries and ideas that shape the world today.
But terpenes can also be dangerous to the plants themselves, Whitehill says. So, for example, in the case of fir, these chemicals are isolated from the rest of the tree’s tissues in a protective fluid that botanists call resin. This thick liquid is kept in special tubes in the outer bark and needles and can be exuded as needed by the tree, such as repairing wounds or reducing the chance of infection. It solidifies when exposed to air, which is why your hands get sticky after handling a Christmas tree. Resin is often incorrectly referred to as sap, but it actually refers to the watery fluid that carries nutrients and sugars throughout the tree. Sap is present in all trees, but resin is produced only in certain species.
The small terpenes have a relatively low boiling point, at which point they turn into gases and produce odors that are detectable by the human nose, producing the typical woody Christmas aroma when the tree is placed indoors and slightly warmed. are these small terpenes, Whitehill says. . However, there is a limit to the amount of terpenes released by the tree, so there is a limit to the scent. This is one of the reasons he recommends decorating your Christmas tree in a cool area of your home. This will keep the tree and its scent fresher for longer.
Whitehill says people with keen noses may notice that the wood’s scent changes while living indoors. “There are several individual compounds with different boiling points, so the aroma of those woods changes over time,” he says.
What Whitehill is most familiar with is the range of terpenes produced by Fraser firs, which make up the bulk of the North Carolina Christmas tree farms where he works. And he says that by sniffing carefully, you can spot slight differences in the terpene profile between these fir trees and other types of Christmas trees. “What I’ve noticed that makes Fraser Fir a little bit unique is that it has a kind of sweet scent, in addition to the holiday bouquet,” says Whitehill. “It has a sweet woody smell, almost like pine, which is very appealing.”
(why do Do many of us really like that scent? Whitehill said he thinks it’s a combination of the scent itself and the memories it evokes of past holidays. )
Whitehill says smaller terpenes can create a woody scent, but larger terpenes can cause a longer-lasting scent. Scientists have discovered a particularly interesting large terpene called cis-abienol in balsam fir. This terpene is strikingly similar in structure to chemicals that have long been used in the perfume industry to produce long-lasting scents. It remains to be seen whether cis-abienol plays a similar role in Christmas trees and whether it can be harvested for the perfume industry.
Another terpene topic Whitehill and his colleagues are researching is whether genetically modifying a tree can change its aroma profile. “Beyond just the classic Fraser fir bouquet, why not get a little crazy and start developing trees like peppermint mocha or mint Christmas trees?” Whitehill says. “How far can I go?”
