(re)discovering water caltrops

I’ll find things popping up in the grocery store from time to time that I’m compelled to buy — afterwards I’ll figure out how to cook them. Usually I have no idea what they are, but this time I saw these brittle bat-wing nuts and a vague memory fell back into my skull.

When I was growing up, there was a jar of these in a dark and dusty recess of the kitchen, along with a jar of dried seahorses. The dried seahorses were unusual enough, but I knew what they were and they fascinated me. In contrast, with the (now identified) water caltrops, these scared the shit out of me. They felt like old beetle casings and must have been dried because hard innards rattled against the shells whenever I shook the jar. My rational young mind figured that they must be ancient scarab eggs, waiting for the right time to hatch in order to crawl into my skin and reach my brain.

Disclaimer: Not from real life. Just a still from The Mummy.

All memory of these horrors must have been repressed because I didn’t think of them for over 15 years until I saw them again here at the Sheng Siong grocery store in Singapore. Now that I’m older and don’t watch (as many) crappy movies, I am ready to face them.


Water caltrops are floating aquatic plants. The black part that I’ll be trying is the seed of the plant. There are many names for it (ling nut, horn nut, buffalo nut, water chestnut, singhara, etc.) which seem to be used interchangeably for two of the three species of the genus (Trapa natans and Trapa bicornis). Trapa natans has four horns. It is considered an invasive species in North America and not commonly eaten. In Europe, it used to be the main ingredient for traditional Italian risotto, but is now endangered and not as widely eaten anymore.

The two horned variety that I have is Trapa bicornis and common in the East. I’m calling it water caltrop because that was the name on the package when I bought it, but in certain regions of India it is referred to as singhara. The Indian recipes I pulled up seem to refer to the red or green Trapa natans.

While looking up water caltrops online, I also found out that caltrops are metal weapons made out of nails or spines. They lie flat like tetrahedrons and are used most commonly now as tire puncturing spikes. It’s easy to see the connection as metal caltrops are similar in shape to the four spiked water caltrops. The word caltrop must have come from the metal weapon first, since this usage dates back to BC times, and then was later used to describe the vegetable (but don’t take me as an etymology expert).

It’s currently the Mid-Autumn Festival (Moon Festival), which is around the time that water caltrops come into season. People in Singapore also eat water caltrops during this time because they look like bats. A part of the characters that spell out “bat” in Chinese sounds similar to the Chinese word for “luck” (fu). Hence, according to this theory of auspicious foods to eat, water caltrops are lucky to eat.

“You called?” “No…that’s just a water caltrop on a harvest moon.”

If possible, I like to try new things in their purest possible form in order to unlock the mysteries of their true tastes. With the water caltrop, it looks like the safest way to try it is after boiling it.

Although the water caltrop can be eaten raw, there are some health risks. Water caltrops can easily pick up toxic metals in bad water or be infected with fasciolopsiasis from fluke larvae. Boiling the water caltrop will neutralize the toxins and infection. Perhaps if I come across a water caltrop that has been grown in clean waters and checked for the snail hosts of the fluke larvae, then I can try it raw one day.

After rinsing, I boiled my water caltrops in water, salt and star anise for 30 minutes.

After they were boiled and cool enough to peel, I went through the arduous process of denuding the seed. I first tried to use a nut cracker on various points — first the horns, then the center, but everything kept on flying away to various corners of the kitchen. The shell is extremely hard and not a very ergonomic shape for shelling.

The trick was to use sharp kitchen scissors. I first snipped off the horns, which were all shell, and then used a combination of carefully cutting into the shell and manually bending and shelling the peel away.

The one “perfect” seed I managed to get out of the shell unbroken

Well, with all that fanfare and exertion, when I finally ate them it was a complete letdown. They are starchy and bland. My partner said that they tasted like a root vegetable (although there are many root vegetables that have delicious flavors). I expected it to be crunchy like a water chestnut, but they’re softer and more mealy. They’re basically more aggravating potatoes.

That takes me to the end of my exploration of water caltrops. I only boiled six of them because I thought that I would use the rest of them for a more exciting recipe. Yet, they were so flavorless and uninspiring that I’m not sure how, and if, I can make something with them. We’ll see!

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