Kentucky Coffee Tree
One of the most enigmatic trees in our landscape. It’s the ghost of a prior era, still holding secrets for us to uncover.
Ancient Footprints
The mammals of the ice age were enormous beyond comprehension for our continent. Mammoths, giant sloths, and camels were among the giant North American animals (also called megafauna) lost in the late Pleistocene extinctions. However, with the loss of these giants came the introduction of one very successful megafauna species - the human.
Humans in the late Pleistocene may have been one of the larger mammals of the landscape, but were among the smallest of the giants walking the continents. We were dwarfed by relatives of the rhinocerous. Outweighed by multi-ton hippo-like herbivores. Hunted by sabertooth cats the size of lions. Outrun by 7’ tall bison.
Many plants went extinct when these megafauna vanished - they co-evolved with giant jaws and feet that no longer moved their seeds around.
Some of these plants were lucky enough to be spotted by ancient humans. In their struggle to survive, the people of the pleistocene learned to process and cultivate foods that didn’t evolve on their behalf.
Consider the Avocado. The enormous pit was intended to be swallowed whole - impossible for our meager throats. But that fruit is still with us today because humans learned the importance of spreading the seeds.
These ancient partnerships result in trees that are rare in the landscape but common near people. Many are foods or have some other use we value (like the bow-wood of the inedible osage orange). By spreading their seeds we continue an ancient bargain made in ages long forgotten.
The Giant Bean Tree
The Kentucky coffee tree is an enigma. The seeds are incredibly hard. When planted they fail to germinate because they’re locked inside the prison of a hard shell. Rasping and cracking (by giant teeth, grinding along rocks, or a human’s knife) release the seed to sprout.
No wild animal spreads the Kentucky coffee tree, and almost none of the seeds produced will ever germinate. This helps explain the tree’s highly limited range. Even in the core of its habitat the KCT is sparse and rarely discovered. Many authors contend that this limited presence is from the loss of megafauna (likely mastodons) which were formerly their primary distributor.
Living megafauna like African Rhinos will happily chomp KCT pods - dropping seeds in dung, ready to grow. Their appetite is likely due to the pod’s close resemblance other bean plants that co-evolved with African megafauna. Connie Barlow noted in her book The Ghosts of Evolution that the African prekese tree is a close analogue - a bean tree that drops enormous pods eaten by elephants and rhinos. Their seeds are rounded to encourage enormous molars to chip but not shatter their coats. Barlow highlights that the Kentucky coffee tree seeds are enormous and almost perfectly round. One can imagine them easily sliding between the molars of giants.
Since the ice age and the subsequent loss of the megafauna, KCT seeds have seemingly been spread by floating along rivers. However, it’s worth noting:
Once liberated from their pods, Kentucky coffee tree seeds sink, they don’t float. Moreover, their roots suffocate and rot in wetland soils. Some of the largest trees (over 100’ tall!) have been found in upland sites, and were cut down as the areas were cleared for farming. Only the sickly riverside trees survived.
Upland sites near rivers are historically those settled by Indigenous nations prior to European colonization. The KCT is commonly found at former Indigenous villages
Chipping the hard seed coat away is important for germination (known as scarification).
Many accounts show the use of Kentucky coffee tree seeds in ceremonial dice games, where markings would be carved into the seed coat.
This leads us to a straightforward conclusion (as it has many others) - the tree may be using rivers to modestly spread today, but it’s here because of people. Humans have been using the seeds and spreading them along settlements, just as they have the avocado.
Poison, do not eat
The beans of the coffee tree are considered toxic and inedible. Livestock have been reported to be poisoned by the leaves and beans. Their symptoms included GI upset and neurological / cardiovascular (heart rate & breathing) changes. At least one dog was reported as having cardiovascular effects after being poisoned.
The chemical most often cited as the cause of poisoning is the alkaloid cytisine. Alkaloids are a category of chemicals that contain nitrogen, usually taste bitter, and are often poisonous to animals. Notably, cytisine has never been found in KCT beans! Instead, scientists have found an array of potential non-lethal compounds which may explain the reports of poisoning.
One researcher looking for the cytisine content, instead discovered a new chemical alkaloid (named diocine) structurally similar to caffeine. The author argued that diocine (which was found to be highest in leaves and unripe beans) was in fact an anti-herbivory agent (aka an herbivore deterrent) and is moderately toxic in animals. Notably, plants that produce caffeine do so to ward off herbivores as well. As KCT seeds became ripe diocine levels drop - leaving large mammals welcome to consume the pods and spread the seeds far and wide.
(Psst! This next section is science terminology heavy. If you get lost, we have a summary at the bottom.)
Diocine appears to degrade during cooking into the stimulant paraxanthine - the main chemical produced as our livers break down caffeine - which is known to be fairly safe. However, it takes two breakdown steps to convert diocine into paraxanthine. Those breakdown steps are where some risks may be hiding.
Diocine itself is what’s known as a derivative of 1,7-dimethyl-isoguanine (which is one of many isoguanine compounds we know of) . The term derivative describes compounds that are structurally similar or can be converted into one another via chemical processes - and so diocine can be considered a potential source of isoguanine compounds. Isoguanines are important to think about when evaluating food safety because they have potential mutagenic (can cause harmful mutations) and other genetic / carcinogenic effects.
As diocine breaks down into the stimulant paraxanthine, it first degrades into the isoguanine derivative 1,7-dimethyl-isoguanine. That means we’re at risk of consuming these potentially toxic compounds if the cooking process doesn’t fully break down all of the diocine.
Consulting with chemists has led us to believe that 1,7-dimethyl-isoguanine is less likely to be mutagenic (and therefore dangerous the way isoguanine is known to be) because of certain structural features. In chemical terms, the methyl group on the N1 group prevents base pairing and thus mutagenic mechanism. The methylation at the 7 position makes it difficult to incorporate a sugar chain there, making it less likely to be processed into RNA or DNA like structures.
Instead of pure isoguanine, 1,7-dimethyl-isoguanine is more likely to act on the parts of our body caffeine does - like the signaling system related to sleep, movement, and eating (the purigenic receptors). The paper on diocine also mentions other unidentified chemicals (methylpurines) present. We don’t know what they are or what their effects are.
(Ok! This is the end of the science-word heavy section. Congrats if you read all that! Here’s the summary for the rest of us.)
So, to summarize in regular English - the beans have a compound we just discovered called diocine. When cooked, it begins breaking down into something similar to caffeine, but first it switches into a potentially dangerous chemical that might cause cancer. A chemist we spoke to says that it’s potentially not a high risk of these effects because of certain chemical traits, and instead might act similar to caffeine. But they also noted that some other chemicals are also present in the bean that we know nothing about yet, and nobody has actually studied what Diocine does to the human body.
Saponins (bitter, soap-like chemicals) have also been found in the KCT beans. These too serve as an anti-herbivory chemical. We have not yet found a publication that describes the rate of saponins throughout the maturation of the seeds, but we suspect they also drop in coordination with reductions in diocine content.
With these chemical assumptions in place, we suspect that the reports of livestock poisoning are due to:
the eating of leaves or unripe beans - where anti-herbivory chemicals are highest.
Intolerance of caffeine-like chemicals (this is why dogs can’t eat chocolate), that trigger cardiovascular and neurological changes.
Consumption of high rates of saponins, which are known to cause GI issues and neurological effects.
Maybe not poison, maybe eat
As the name might suggest, numerous accounts describe the Kentucky coffee tree as being a coffee substitute where the seeds were roasted and then ground up before brewing. Like we described before - if there is indeed a caffeine analogue, then there would be a stimulant effect from this coffee replacement though less prominent in mature beans. The seeds have also in certain places and times been roasted and eaten like chestnuts.
Contemporary foragers have begun experimenting with eating Kentucky coffee tree beans directly. Their cooking methods typically involve either the roasting of mature beans, or the boiling of immature beans.
We experimented with nixtamalizing (boiling in an alkaline solution) the mature seeds. This turned the hard shell into a waxy rubber that could be peeled away easily. The beans were quickly shelled this way and were quite tasty.
This all leads us to believe that the kentucky coffee beans likely have a mild stimulating effect (because they contain diocine, which likely degrades into paraxanthine during cooking). This effect is reduced as beans mature and diocine content reduces.
There are also saponins present which are likely an anti-herbivore defense. If so, the saponins are potentially lower in the mature beans as well. Saponins are water-soluble, meaning they dissolve into water easily. Foods that contain saponins (such as other closely related plants like chickpeas and kidney beans) are often cooked by boiling, which removes significant amounts of saponin.
Mature beans therefore - especially when cooked in water like other beans- likely have the lowest rates of potential chemical effects on the body. With that in mind, the following risks remain worth considering:
There is a potential for carcinogenic / mutagenic effects, especially when undercooked (though again, we believe the risk to be fairly low, it is still non-zero and understudied).
One can expect systemic effects to similar caffeine, with potentially similar health risks for sensitive groups.
There are other chemicals present, and we don’t know what they are or what they do.
We don’t know the long term effects of consumption at any dose, or with any preparation method.
For those deciding to try consuming the beans, it’s important to take these risks under consideration. Starting slow and cautiously in very small amounts is a good idea.
Looking ahead
We’re not just fascinated by this tree as being a lost food. The KCT has unique strengths which make a potential human ally in a changing world.
First and foremost, nothing eats these beans. Every year they pile at the feet of trees uneaten by any pests. Researchers easily collected 25 gallons in a manner of minutes, and reported that truckloads remained. If this is indeed a food, it’s shelf stable and isn’t at risk of pest damage the way that other seed crops are. You don’t even have to harvest them - just collect the beans as needed from the ground. Although nobody has studied their nutrition, as beans one can assume they’re a good source of protein (which is a relatively difficult macro-nutrient to produce).
The tree is also unique in its fear of winter. The KCT leafs out only in the early summer, which protects delicate buds from late frosts. This makes it an excellent temperature modulation tree to mitigate climate extremes - allowing for both spring sun and summer shade. They’re also highly tolerant of city conditions - thus they’re prime candidates for reducing urban heat islands through street plantings.
Finally, the tree is tolerant of environmental extremes. inaturalist distribution maps show populations ranging from Texas to Toronto. This means that if you don’t know the climate future of a region (which will continue to be more and more common as our models deteriorate), KCT is an excellent survivor to bet on.
Keeping Promises
Some scientists believe the bean’s beautiful smooth appearance forged the original partnership with humans. Tokens for games, gambling, and scrying the future. Perhaps our suspicions are right and food was also a primary use. But regardless of the reason, the KCT remains alive because of humans. But maybe not for long.
The Kentucky coffee tree is vanishing - already rare, and getting more sparse in each passing decade. We’ve failed to uphold our end of a deal. A promise we made during a time of great dying in the landscape as the giants fell. In many ways a time not so dissimilar to the one we’re living through now.
This is a lesson we continue we’re taught over and over again, but fail to remember. It’s our job to maintain the agreements between humanity and landscape - especially those forged long ago. When we shirk the duty of regular burning in fire country, the catastrophic forest-killing flames sweep through. Overhunt the beaver and our crops fail in droughts. Deny the Cherokee their traditional harvest of Sochan, and see the plant grow weaker. People and land have always had promises to one another - and we shirk them at our own peril.
So plant the Kentucky coffee tree. Enjoy the beauty of the seeds. Sit in the summer shade, the spring sun. Learn from the caution of leaves emerging long after the last frost. Eat the beans (if you accept the risks). There is an old pact between us that should be maintained. This world is generous - but only if we remember that promises are to be kept, and the land is kin.
Hi! What ratio of cal/water did you use, and how long did you boil the seeds? I'd love to recreate this. Thanks in advance!