For chefs to make the best sushi or sashimi they need to use the freshest fish as material.
A common way to ensure this is to always have existing fish available to be used in the restaurant for slaughtering by keeping them in an aquarium fish tank.
Using this method the fish that’s used would only be dead for a few minutes before it is freshly cut and served.
The drawback with this method is that you might find the just-served fish still twitching despite it being already beheaded and gutted. And also the fresh fish meat will be very chewy and lacking any real flavors to the meat.
While this way of serving half-alive fish is popular in many Asian countries, you should be careful and eat at your own risk.
The problem with serving fish straight out of the tank and thus maintaining its high freshness is that there are higher chances of having parasites in the fish.
That’s why there are many regulations in the US for supermarkets to have their fish frozen. By having the fish pre-frozen at low temperatures before sale the parasites that’s living in the fish would be killed.
Variations That Affects the Time
But this is not the case for all sushi fish that is used, due to the fact that there are many suppliers available for a marketplace or seller to choose to get his fish.
While fesh slaughtering takes the least time, the fishes that are sold in general markets have been frozen when they are catched on the ship. This method is called flash freezing where the objects are frozen quickly at temperatures below -54 degrees Fahrenheit.
That’s why the exact amount of time the fish has been dead before it is served in a sushi restaurant can range from weeks to many months. Because a large part of this question depends upon three factors.
Firstly, how long the fish have been frozen after they are catched before the ship arrives at port. To this question most boats stay at sea for days or even weeks at a time.
Some vessels are out for more than 70 days, and many Japanese and Korean fishing boats stay even longer for over 2 years continuously.
Secondly, the time for the imported fish to be shipped overseas to their specific destinations can vary from a day using a plane to over 2 weeks by a container ship. The time for most ships to cross the pacfic ocean from Asia to the US takes about 23–30 days.
Lastly, another factor that can lengthen the time after the fishes are bought by restaurants is the amount of days for aging.
Aging Sushi Fish
An important thing that you must keep in mind is the fact that sashimi are not used immediately by most sushi restaurants. Instead, it is common for sushi chefs to age the catch to bring out the best flavor in the meat.
Many top chefs choose to carefully age their fish for about 3–10 days, though the exact amount of aging is decided from the type of fish and the chef’s preference.
But the practice of aging a fish to its peak amount of umami(Japanese word for savoriness) is not an easy skill to learn. That’s why it is not common to see this practice done to the fishes that are used to make the rolls for sushi conveyor belts.
The inherent difficulty is knowing the proper amount of aging needed to reach peak umami without the meat going stink.
It can be compared to the curves on a roller coaster where aging for most fish might take many days. While the ‘drop’ of the roller coaster is only about a few hours before the fish loses that maximum flavor.
