Most people know katsuobushi as a bonito flake seasoning, but it can also be a blade.

At first glance, katsuobushi (dried bonito) seems like one of the softest ingredients in Japanese cooking. I mean, when it’s used as a topping for the crepe-like okonomiyaki, katsuobushi flakes are so delicate they actually sway back and forth from the heat rising off the rest of the dish.

But the truth is that before it’s sliced, katsuobushi is ridiculously hard, with some claiming it holds the record as the hardest food in the world. As a matter of fact, pre-shaved katsuobushi is so hard that you can make it into a knife.

That might sound like the kind of knowledge you could only acquire in a Japanese prison, or maybe a shank-centric anime series, but Japanese YouTuber Attoteki Fushinsha no Kiwami has created a video demonstration. First, though, let’s run through the basics of how katsuobushi is made. To start, the fish is filleted, simmered, deboned, and smoked multiple times. It’s then dried and allowed to slightly ferment, and the start-to-finish process can take weeks to complete.

▼ When it’s all done, the katsuobushi looks like a piece of wood, and has to be cut with a special tool that resembles a woodworking plane.

In its solid form, katsuobushi is hard enough to be used as a hammer, as the demonstrator shows here.

Because they start out as fish fillets, chunks of katsuobushi already have an oblong, vaguely knife-life form. So with enough grinding, you can get katsuobushi to hold an edge, and we can see the blade really starting to take shape here at the video’s six-minute mark.

After some more grinding, the basic shape is done, with an untreated portion at its base acting as the handle.

At this point, the demonstrator pops his fish blade into the oven for an hour to bake at 100 degrees Celsius (212 degrees Fahrenheit). Once that’s done, he sets up a whetstone for the final sharpening, as seen in the video here.

Once the demonstrator thinks it’s ready, he tests out the katsuobushi knife on a sheet of paper, and finds it slices as surely as scissors.

Even more amazing is that the tip is sharp enough to punch through an aluminum can!

Granted, Attoteki Fushinsha no Kiwami himself has shown us that in Japan, you can go to the store and buy a perfectly usable knife for just 100 yen (US$0.89). But still, it’s nice to know that if you have a block of katsuobushi, you not only have the means with which to season your cooking, but to chop the other ingredients too.

Source: YouTube/ ! 圧倒的不審者の極み via Sploid
Images: YouTube/ ! 圧倒的不審者の極み

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