Hello, this is SUSHI SHUTATSU.

Today, I’d like to dive deeper into the science of sushi aging, one of our core specialties known as “Jukusei: “Aging” (Jukusei). You may have heard that letting fish rest makes it taste better. But today, I want to move beyond intuition and explore the mechanism behind this process from my perspective as a former chemistry major.

It might get a little technical, but please bear with me as we explore the science behind delicious sushi.

The Sushi Aging Process is an “Enzymatic Reaction”

Let’s start with the conclusion. At SUSHI SHUTATSU, aging fish means “using the fish’s own enzymes to chemically transform muscle components into ‘umami’ compounds.”

Freshly caught fish has a firm, springy texture, which is enjoyable, but it actually lacks significant “umami” flavor at that stage. The key player here is ATP (Adenosine Triphosphate), the energy source for living organisms.

The Breakdown Process of ATP : The Source of Umami

While a fish is alive, its muscles are abundant with ATP. However, once the fish passes away, new ATP is no longer produced.

This is where the aging process—the chemical reaction—begins. Enzymes in the muscle start breaking down the remaining ATP in the following sequence:

• (Simplified Text Diagram)
  • ATP (Energy source) ↓
  • ADP ↓
  • AMP ↓ Enzymes work their magic here
  • ⭐ IMP (Inosinic Acid = The Source of Umami!) ⭐

Once it breaks down to AMP (Adenylic Acid), enzymes work further to finally produce the substance we crave: IMP (Inosinic Acid).

This “Inosinic Acid” is the true identity of the intense umami found in things like bonito stock dashi. Therefore, aging is essentially “the time spent waiting for ATP in the muscle to break down and convert into inosinic acid.”

The Trade-off : Texture vs. Umami

Here is where it gets even more interesting. There is a significant relationship between this chemical change and the “texture” of the fish.

Immediately after death, the remaining ATP causes the muscles to contract rigidly. This phenomenon is called “rigor mortis.” Fish in this state has a distinctively fresh, “springy and firm” (puri-puri) texture. However, as mentioned earlier, the umami content is still low at this point.

As time passes and ATP is depleted, rigor mortis resolves, and the flesh becomes softer. It is precisely at this timing that inosinic acid increases explosively.

In other words, aging is a trade-off: sacrificing the initial “firmness” to gain a “tender, rich, and sticky” (nettori) texture along with profound umami.

Pinpointing the Peak

We can’t just wait indefinitely. If too much time passes, inosinic acid breaks down further into hypoxanthine, losing umami and eventually leading to spoilage.

The speed of this chemical reaction varies depending on the fish species, size, temperature, and water content.

The job of SUSHI SHUTATSU is to identify the exact apex of that graph—the moment umami is maximized while freshness is perfectly maintained—and slice the fish at that precise instance.

The Taste of Science in a Single Piece

This may have been a bit theoretical, but when you are sitting at our counter, I hope you simply enjoy the flavor and think, “Delicious!”

Perhaps knowing that “Ah, this is the taste of ATP turned into inosinic acid…” might add a different layer to your dining experience.

We look forward to serving you sushi toppings that have reached their ultimate peak of umami.

Reserve Your Seat at SUSHI SHUTATSU

Enough theory. It’s time to verify the results with your own palate. We are waiting for you at the counter with the perfect slice, expertly calculated to reach the pinnacle of umami.

👉 https://inline.app/booking/SHUTATSU/SUSHI?language=en

We are sincerely looking forward to welcoming you soon.