Recently, a client was picking up a piece of furniture at my house. As they were leaving, they commented, "Does your living room always smell like wood and finish?" People often comment on the smell of the shop — "I love the smell of wood shavings!" or "This reminds me of my grandpa/dad." We appreciate wood with our senses, but we often focus on visual character (color of the wood, grain patterns) or tactile perception (smooth and glossy or textured) rather than smell. Sometimes smell is an equally important part of the final product. However, in most cases the woodworker is the one that really gets to sense and appreciate the smell of wood. A piece of walnut passes through the planer and the shop fills with a forest musky scent. I stick some fir molding with a hand plane and a whiff of resin-y freshness slips past my nose. I rip some cherry on the tablesaw and there is a distinct sweet-spicy smell that quickly picks up a smoke scent as the wood pinches and burns a bit. I love the smells of the shop.

Figure 1. Planing bench at the Amana Colonies, Iowa.

The aroma of wood comes from an incredibly complex chemical factory in trees that is constantly mixing and making molecules, turning sunlight, water, carbon dioxide, and minerals into all the "stuff" of wood.

About 70% of wood is cellulose (C₆H₁₀0₅) and hemi-cellulose, the polymers that make up the cellular structure of wood. About 25% of wood is lignin, the glue that holds the cellulose together. The remaining 5% of wood is extractives — non-structural components of wood like sap, resins, and gums that are moving around in the cells of the tree. Phloem sap is the sugar-rich blend that travels from the leaves to the sugar sinks in tissue of the tree. Xylem sap is the goo moving from the roots to the leaves to supply the photosynthesis factory. Specialized cells in trees also produce chemicals like resins (to heal wounds) and tannins (function as an insect repellent). When a tree is turned into lumber, all of those juices are locked up in the cells giving wood its color, odor, and some of its physical characteristics.

A recent study of Scots pine (Schreiner et al, 2018) explored the odor composition of trees grown in Germany. They detected 44 odor-active compounds in the overall smell of pine. These read like an ingredient list on a bottle of sugary drink and include things like (E,E)-nona-2,4-dienal, vanillin, phenylacetic acid, 3-phenylpropanoic acid, δ-octalactone and α-pinene. Some of these compounds are made directly by the tree, some are the result of things like lignin and fatty acids breaking down as the wood dries or is exposed to air. Like a complex perfumer's fragrance, the essence of Scots pine is the unique blend of 44 different aromatic "notes" that sing the song of the tree.

Figure 2. Freshly cut ponderosa pine, can you smell it?

The complexity of smell makes it very hard to describe. Try and tell someone what walnut smells like. You will struggle, maybe say something like woodsy-musky, but you will probably feel like you didn't quite capture the true essence of the smell in your words. It is a bit like naming the colors in a box of 64 crayons — burnt sienna sunset, orangey brown, daisy yellow. Often, we fall back on describing wood smell by naming a common product that uses that wood instead of qualifying the aroma itself. A few of the woods I have been working with lately are:


There are a number of applications where wood aroma really matters. Cedar closets and blanket chests, for example, use the natural repellent property of cedar oil to discourage bugs. If you make a storage box that is going to hold something with its own unique flavor and aroma (cigar humidors, tea chests) you need to consider the effects of the aroma of the wood you use. Wine is a particularly important case where the exchange of flavors and smells between the wood and the product creates the signature bouquet. And finally of course, there are wood-based fragrances for perfumes and colognes like "Sawdust" or woodshop-scented candles and air fresheners.

Some of the most expensive wood in the world is agarwood which is the source of oud oil. Agarwood is rare because it only forms in the heartwood of Aquilaria trees when they are infected by a specific fungus. The tree reacts to infection by infusing the heartwood with a dense, fragrant resin. The dark heartwood is agarwood or oud. Maybe 1 in 50 trees creates agarwood and it takes about 8 lbs of oud chips to make 1 ml of oud oil. Known and traded since ancient times, the unique fragrance and rarity of oud oil has earned agarwood the nickname of "wood of the gods." Some of the aloewood mentioned in the Bible was likely agarwood.

Which brings me to why are we paying $300/ml for oud oil or $30 for a candle that smells like Granddad's Workshop? Olfaction is powerful sensory input. We like things that smell nice, and we recoil from things that stink. Some of this is probably baked into our very beings through evolution that puts a premium on survival and reproduction. Recent research (Ikei et al, 2017) summed up studies on the physiological effects of smelling wood odorants (cedar and cypress and pine). A good whiff of pine can drop your heart rate, blood pressure, and stress.

But perhaps the strongest effect of smell is its power to evoke memories. This is known as the Proust phenomenon, the sudden, vivid, and emotionally-rich recollection of autobiographical memory triggered by odor. Scientifically, the theory is that your nose is connected more directly to parts of the brain that process memory and emotion compared to other sensory inputs. Smells have a stronger connection to memory and are able to retrieve the past in ways that sounds and sight do not. My brother's first response to the smell of Doug fir is a vivid recollection of cutting lumber in the garage — an old, autobiographical memory with a strong emotional component of happy times making things with Dad.

Helen Keller said, "Smell is a potent wizard that transports you across thousands of miles and all the years you have lived." So I am sitting in my shop today surrounded by walnut and cherry and pine and fir and catalpa. There is a Camellia Oil-soaked rag ready to wipe the bench planes, a bottle of hide glue on the bench, the SC Johnson paste wax buffing cloth, and the WD-40 I just used to lube the tablesaw. I close my eyes, and the fragrant blend of hundreds of odors mixing with the dust motes in the air takes me back to workshops past, being an 8-year-old in a shop with violin varnish curing in a cabinet, piles of aluminum swarf and cutting oil, watching Grandpa carve a ball in a cage sitting at his bench--whispers of stories from Grandpa's workshop. Priceless.


References

Ikei, H.; Song, C.; and Miyazaki, Y. 2017. Physiological effects of wood on humans: a review. J Wood Sci 63, 1–23..

Schreiner, L.; Bauer, P.; and Buettner, A. 2018. Resolving the smell of wood-Identification of odour-active compounds in Scots pine (Pinus sylvestris L.). Sci Rep 8, 8294 (2018).

Bob Rummer lives in Colorado and is a part-time woodworker. He can be reached directly via email at rummersohne@gmail.com. You can see his shop and some of his work at www.JRummerSons.com.

Return to the Wood News Online front page