The landscapes of the Americas are littered with what’s called anachronistic trees; species that coevolved with megafauna that once were the primary distributer of seed and genetics. With the passing of those massive mammals, from the late Pleistocene extinctions— a perfect storm of climate change and human expansion— their slow passing on the landscape has been outside of the scope of human tools of measurement.1 Hidden away on the landscape are large, strange fruits that go uneaten by wildlife— pawpaws, honey locusts, osage oranges, black locusts, and Kentucky coffee trees.
While we picture the megafauna meaning the mastodon and wooly mammoth, oversized beasts similar to many of the larger species of Africa once called North America home— sabertooth cats the size of lions, bear-sized sloths called Nothrotheriops, car-sized armadillos called Glyptotherium, and so many more. These monstrous animals demanded larger foods, and the fruits and seeds they feasted on found themselves alone after their rather quick extinction. While many disappeared quickly, those few that remain stand out in a landscape they never evolved for. But many found new mates with the primates who repopulated the landscape.
The Kentucky coffee tree is one such plant. As humans learned the landscape, these oversized fruits and seeds offered a massive caloric input, if they could be processed. Today, the seeds are largely considered inedible. Yet, the trees are almost always found near Indigenous settlements.2 So the question remains; if they are inedible, why were they so revered that they were planted so close to home?
Borrowing from my good friend over at Pyrophytic Futures (who has written about KCT, which I’m borrowing from extensively— subscribe to their great work!), there’s quite a bit to unpack about this unique tree. Before we can discuss its historical role with humans on the landscape, let’s look at the bean itself.
Right away, it’s obvious that it’s a bean— it dangles from the trees in green pods that look like comically oversized snap peas, and the beans themselves are nickel to quarter-sized. By most researchers, they’ve been considered both toxic and inedible. Similar to other anachronistic trees (such as black locusts), livestock have been reported to have been poisoned not just by the beans but the leaves as well.3 The chemical that has been the focus of the research regarding its toxicity is alkaloid cytisine. Alkaloids contain nitrogen, taste bitter, and are often poisonous to animals. However, there’s never been cytisine found in the beans— but that doesn’t mean that there are no other compounds of concern.
One researcher, in his quest to prove the cytisine content of the beans, stumbled across a new chemical alkaloid named diocine, that is structurally similar to caffeine.
And for a more detailed explanation of how diocine works, I’ll defer to Pyro:
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.
In short, the compound in the beans breaks down when cooked into something similar to caffeine, but first, it switches into a potentially dangerous chemical. However, there are still other chemicals that are understudied in the beans that have the potential to be harmful. This trait— the caffeine-like compound— also explains the name of the tree— as it was often described as a poor coffee substitute for colonists as they expanded west. It was actually a selling point; Kentucky was “a place where a tree grew with beans that could be roast and brewed to make a fine coffee substitute.”4 Anyone who has tried this drink will tell you that this is not the case. In fact, in 2003, researchers decided to recreate written recipes to make coffee from the Kentucky Coffee tree.5 According to the test results, “No one claimed to enjoy the taste or the experience.”
Keep reading with a 7-day free trial
Subscribe to The Poor Prole's Almanac: Restoration Agroecology to keep reading this post and get 7 days of free access to the full post archives.