It’s a well-known fact among professional chefs that some fish don’t rely solely on freshness. Of course there is importance in freshness, but that’s just one element. It’s generally understood that flavor and taste improve with time (maturity).
The umami* found in the meat of the fish is essentially inosinic acid and glutamic acid. After a certain amount of time has passed after a fish has died, the body stiffens and not long after that the rigor lets up. The inosinic acid, which the umami is composed of, comes after the fish has stiffened. It then accumulates in the process of the body relaxing. This is the same in beef and pork in which there is no umami in the meat unless it is hung and matured for a time.
Therefore, ikizukuri sashimi that is still twitching usually won’t have the taste or depth of umami. However, the firm texture of sashimi is also an undeniable enjoyable aspect. It is not all about the umami.
*Glutamic acid, Inosinic acid and Guanylic acid are representative components of umami. Guanylic acid is found in kelp and vegetables (tomato, Chinese cabbage, green tea, etc.) as well as Parmesan cheese, inosinic acid is found in fish (bonito, macheral, sea bream, etc.) and meat (pork, chicken, etc.) while Guanylic acid is abundant in mushrooms (especially dried shiitake mushrooms).
We hope this information will be helpful.
Revision date: July 17, 2017