Mold-Aged Tuna – a furry, controversial Japanese delicacy

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1 day ago Pavel

Mold-aged tuna is one of Japan’s rarest and most controversial culinary delights, involving the dry-aging of bluefin tuna under a thick layer of (furry) mold.

Looking at a 4-week piece of mold-aged tuna, you would swear it was some kind of furry creature, due Koji mold (Aspergillus oryzae), that appears as a thick and fluffy layer.
But while mold will put a lot of people off, in this case, it is an essential ingredient that makes bluefin tuna more delicious.

To mold-age tuna, Japanese chefs store pieces of fish in very specific conditions, usually at temperatures between 1 and 6 degrees Celsius and humidity between 70 and 85%, encouraging the development of Koji mold.
And, over at least four weeks, although some chefs will let the mold grow for eight weeks or more, the fish becomes completely covered in a furry-looking layer of mold.
Believe it or not, under the unusual layer of “fur,” enzymes gradually break down proteins and fats, releasing amino acids, which results in a deep “umami” flavor, more precisely rich, slightly nutty, sometimes with meaty undertones, and the meat is also considerably more tender, to the point where it melts in your mouth.

But don’t worry, If you’re scared about eating that furry shell, the mold is carefully trimmed off, leaving only the aged tuna, which is usually served raw as sashimi or sushi.
Because tuna is a delicate fish, this process is generally handled by top-tier chefs in controlled environments, as uncontrolled mold can produce harmful toxins (mycotoxins) and cause severe food poisoning.
Either way, because of its deep, concentrated flavor, it is one of the rarest and most controversial luxury experiences in modern sushi.