By now the scene is familiar: you’re sitting at an upscale sushi restaurant around a counter, presided by a Japanese chef — the itamae. His hands move with a fluid grace. You watch as he gently presses a slice of chutoro – or fatty tuna belly on a clump of rice. The pressure is enough for the two surfaces to kiss without rupturing either of its delicate form.
The taste? Exquisitely umami and as soft as silken pillows.
It’s tempting to think that the quality is because the fish is fresh. After all, such high end sushi restaurants often boast flying in top-notch produce several times a week from Tsukiji Market in Tokyo. But here’s the kicker: the best seafood in these premium omakase-style spots is not actually fresh. In fact, it can be as much as one month old, thanks to an ageing process that skilled Japanese chefs all over the world use.
“By ageing fish, we can improve the flavour and the textures of the fish,” says chef Masashi Kubota of Taka by Sushi Saito. The restaurant at the St Regis Kuala Lumpur is the local offshoot of the three Michelin starred Sushi Saito in Tokyo.
“If the tuna belly wasn’t aged or wasn’t aged enough, [it] would taste a little bland, really fatty, and the veins in the belly would be really hard to chew through,” he says. “It would just be like eating a tasteless, chewy fatty slice of fish.”
It seems an odd phenomenon given that Tsukiji Market – the Mecca of fishermen, purveyors, chefs and gastro-tourists alike — is ringed by sushi restaurants whose selling point is that the source of its seafood is a hop and a skip away.
But that by no means masks the high level of techniques and precision required to serve quality cuts to diners. As with many Japanese crafts, ageing is an art — not simply a matter of shoving a slab of raw fish into the fridge and waiting for the gods to work their magic.
The process begins with ikejime, a technique executed by the fishermen or fish suppliers. Here, the brain of the fish is first crushed and a metal rod is inserted through the length of its spine. Doing so paralyses the fish and prevents the release of lactic acid and cortisol that otherwise takes place when a fish is stressed; such responses are said to lower the quality of the meat.
“[Ikejime] allows the fish to stay fresh at a longer period of time, and to preserve the fish whilst it’s being transported,” says chef Masashi. “When it arrives, it gives us the best product to age with.”
Chefs from the best sushi restaurants around the world age their own fish as it gives them complete control over the end product. The method also differs between types of fish.
“There are many ways to ageing from salting to pickling to wrapping it in konbu — a process known as Konbujime,” explains chef Masashi. “The range of ingredients used for ageing is vast, but the most basic ingredients that are normally used for ageing are kelp, salt, vinegar and ice.”
The fish is then kept at a temperature between 1°c to 4°c to prevent bacterial growth and aged anywhere from five minutes to a month, depending on the fish and type of ageing.
This allows the natural enzymes to break down the fish and for moisture content to evaporate, leaving behind meat that’s tender and umami.
“The duration of each process depends on how fatty or lean the fish is and also on how big the fishes are,” adds the chef.
Ultimately, what differentiates a sushi restaurant as a cut above the rest is the technical know-how behind each serve. So the next time you dine at a good sushi restaurant, ask not when the seafood arrived, but how tenderly it’s been treated before it’s placed in front of you.