— A Sushi Chef’s Way of Thinking About Osmosis —
Have you ever thought,
“This fish smells a bit fishy…” even though it looks fresh?
In many cases, the problem isn’t the fish itself.
It’s the moisture inside and on the surface of the fish.
Fishy smell comes from moisture, not the flesh
Fish contains a large amount of water.
After a fish is harvested, certain compounds responsible for fishy odors (such as trimethylamine) begin to form. These compounds dissolve easily in water, especially in the liquid that seeps out of the fish, often called “drip.”
In other words:
- Remaining moisture
- Surface drip
- Excess liquid trapped in the flesh
These are often the real sources of unpleasant smell.
That’s why in sushi and Japanese cuisine,
controlling moisture is the same as controlling odor.
Why simply patting fish dry makes such a difference
Even fish bought at a supermarket can improve dramatically if you:
- Gently pat the surface with paper towels
- Remove excess moisture before cooking or serving
When you remove water, you are also removing the odor-causing compounds dissolved in that water.
This is one of the biggest differences between
“fish that smells at home” and
“fish that doesn’t smell at a sushi restaurant.”
Salting fish is not about seasoning
When people hear “salt the fish,” they often think it will become salty.
But in professional kitchens, salt is not used for flavor here.
It is used to move water.
The key concept: Osmosis
When a small amount of salt is sprinkled on fish:
- Inside the fish: low salt concentration
- On the surface: higher salt concentration
Water naturally moves from the inside to the outside to balance this difference.
This movement of water is called osmosis.
As the water comes out, it carries with it:
- Excess moisture
- Blood residues
- Odor-causing substances
The result is fish that smells cleaner, tastes clearer, and has a better texture.
In sushi kitchens, this process is often thought of as
“cleaning the fish,” not seasoning it.
What you can easily try at home
You don’t need professional tools to apply this idea.
1. Remove surface moisture
- Pat the fish dry with paper towels
- If you rinse the fish, always dry it thoroughly afterward
2. Lightly salt the fish (5–10 minutes)
- Just enough salt to lightly coat the surface
- When moisture appears, wipe it away with paper towels
3. Avoid sealing in moisture
- Wrap the fish with paper towels, then loosely with plastic wrap
- This prevents moisture from returning to the flesh
These small steps can:
- Reduce fishy smells
- Improve aroma when cooking
- Make flavors cleaner and more refined
Fish quality is not only about freshness
Fish is an honest ingredient.
- Leave excess water → odors develop
- Control moisture → flavor improves
The reason fish at a sushi counter doesn’t smell fishy is not magic.
It’s the result of careful handling and constant attention to water.
Next time you prepare fish at home,
try thinking not just about freshness, but about moisture.
You may find that the fish you thought you knew
tastes completely different.
If you’d like, the next article could explore:
- Why dark meat (bloodline) smells stronger
- Why properly aged fish doesn’t smell bad
- The difference between oily fish and white fish in moisture control
This topic makes a great series.
If you’re visiting Tokyo and looking for an authentic sushi experience, we invite you to enjoy a carefully crafted omakase at Sushi Shutatsu in Ogikubo.
Our chef prepares each piece using traditional Edo-style techniques, premium ingredients from Toyosu Market, and warm Japanese hospitality.
We look forward to welcoming you and sharing the true taste of Tokyo sushi.
