Tapping Black Walnut Trees

In my backyard there are two large black walnut trees. A few weeks ago a friend helped me tap them. I’ve never made or tasted black walnut syrup before, so I was glad to have some New-Hampshire-ian expertise on deck.

The process was actually quite easy; after drilling the holes and hammering in the spiles, the trees slowly dripped out their lightly sweetened tonic. About once a day I collect the sap, strain it, store it in the fridge, or (if I have enough time and sap) boil it down. Two trees’ worth of sap is so little that I really don’t expect much syrup. I’m mostly interested in the experience and the chance to know if my homemade sweetness tastes any different than mass-produced syrup.

Subtlety of Flavor

The boiling process was shockingly lovely. I spent hours watching crystal clear liquid slowly darken while clouds of aromatic steam billowed into the kitchen. The smell of a heavenly pie has been known to lift cartoon characters clean off their feet; I am decidedly not a cartoon character. When the kitchen filled with rich and intoxicating natural fragrances, I looked more like a crazed bloodhound than a floating angel. I frequently leaned my head deep into the steaming vessel to inhale the sweet, woody aromas. Apparently, a few extra inches of atmosphere between the bubbling sap and me was an unbearable inhibition.

The olfactory system of a human is able to identify over one trillion unique scents [4, p 32]. This ability is not without function; though it may not be evident to the individual, humans’ perception of odor goes beyond distinguishing fresh from rotten food. The human nose is so fine tuned that it may detect natural fragrances released by other humans due to anxiety, fear, aggression, or sexual availability.

By experience, and without deep knowledge of biology, most people can accurately identify that scent is deeply connected to taste and cravings. The nasal cavity is located above the roof of the mouth, and inside it are over four hundred kinds of smell receptors [3, p 45]. When aromatic compounds from foods aerosolize and make contact with the numerous small receptors, the olfactory bulb is activated in the brain. The uncountably large number of ways that fragrant molecules can stimulate these receptors is what accounts for our ability to distinguish the flavor of chicken from the flavor of beef, or vanilla from chocolate cake. The human tongue (along with the roof of the mouth and back of the throat) is equipped with taste receptors that can distinguish five basic tastes; sweet, sour, bitter, salty, and umami [3, p 46]. These receptors make up the powerhouse of the human’s sense of taste, but are tactless with the distinction of more complex flavor. As an over-simplified example, the consumption of ice cream may give rise to an entirely different flavor experience than the consumption of a lollipop, but as far as the taste receptors on the tongue are concerned, it is possible that these two foods only differ in degree of sweetness.

As I leaned over the pot, I wondered what I was smelling. I knew the smell of cane sugar dissolved in water, and this wasn’t it. I had never tasted walnut syrup before, but somehow, by smell alone, I knew it would be a leathery, earthy food. There was no wood fire during any of the processing, but I could tell the syrup would taste smokey and maybe even a bit bitter like a good dark chocolate.

Since its advent in the 1950s, gas chromatography has been the leading scientific tool used to determine flavor compounds in food [3, p 48]. Aromatic compounds boil at different temperatures. By heating a test sample to different boiling points in the presence of a detector, a gas chromatographer not only produces a list of chemicals present in a sample, but also reveals the proportions of each chemical. By reading the results of this machine, one could determine what the food sample tastes like. Of course, that is the information which interested the flavor industry. However, I find it amazing that the nose, which just happens to come free with the being-a-human thing, is able to distinguish chemical compounds better than this expensive machine.

Yet more than mere taste, noses are intimately connected to the brain where the experience of flavor can be directly interpreted, evaluated, and associated with nutritional value and memories. When I smell black walnut syrup in the future, I may forever be reminded of sticking my head into a pot to get a deeper whiff of the burbling elixir.

Even if a flavor compound has no nutritional benefit, due to the power of association it still has strong implications for nutrition. The flavors we grow to enjoy are the flavors our brains associate with desirable post-ingestive results [3, p 98]. In the same way that feeling thirsty drives us to rectify the condition of dehydration, cravings are the brain’s way of driving us to rectify nutritional imbalances by eating specific foods. This may even be extended to addictive substances such as tobacco or sugar, in which a craving alerts the conscious mind of an imbalance of the dependent chemical, and pleads for ‘a fix’. In light of this, it seems that flavor is, on the whole, an ‘acquired taste’. As the body realizes the usefulness or benefit of a food, that food becomes more tasty.

Minerals In The Syrup

So what is in my walnut syrup, that it should taste so much better than boiled down sugar water?

Minerals, for one. One liter of black walnut sap contains 100% of the daily recommended copper intake [1, p. 676]. The sap also contains zinc, magnesium, calcium, sodium, and potassium. Considering that the boiling point of these minerals far exceeds the boiling point of water, (calcium, for example, boils at 2,703 degrees Fahrenheit), the minerals will be retained in the syrup [2].

Unfortunately, I struggled to find much research on the vitamin and antioxidant content of black walnut syrup. Maple syrup, however, is more widely discussed and often cited as containing large amounts of polyphenols and vitamins. Given the nutritional breakdown of maple syrup, it isn’t unreasonable to imagine that there are also antioxidants and vitamins in my black walnut syrup. Without satisfactory research to cite, however, I think I will leave this as a happy consideration in my head.

I hope that I may tap these trees again next year.

Citations

[1] Bilek, M., Stawarczyk, K., Gostkowski, M., Olszewski, M., Kędziora, K., & Cieślik, E. (2016). Mineral content of tree sap from the subcarpathian region. Journal of Elementology, (3/2016). https://doi.org/10.5601/jelem.2015.20.4.932

[2] Royal Society of Chemistry. (2023). Calcium – element information, properties and uses: Periodic Table. Calcium – Element information, properties and uses | Periodic Table. Retrieved February 19, 2023, from https://www.rsc.org/periodic-table/element/20/calcium

[3] Schatzker, M. (2016). The Dorito Effect: The surprising new truth about food and flavor. Simon & Schuster.

[4] Sheldrake, M. (2020). Entangled Life: How Fungi Make Our Worlds, Change Our Minds and Shape Our Futures. London: The Bodley Head.