Since the late 1980s when the market for snapper exports to Japan really took off, the iki jime method of killing fish spread and it has now become de rigueur for many amateur anglers.
But there are also many opponents who believe iki jime may be the best way to handle the tonnes of fish that long-liners bring aboard but that recreational fishers can treat their catch even better by simply dropping the fish into a chilly bin filled with a saltwater slurry. The spiking method opens a hole for bacteria to attack and thereby causes a rapid deterioration of the fish flesh, they say. And the spike can induce a rush of blood through fillets.
It is this blood flow, and the onset of rigor mortis, that needs to be prevented in order to ensure the flesh tastes best and lasts longest. Rigor will set in after three to four hours if fish is not treated well. It can take up to 24 hours to develop in fish that are iki-killed.
To the Japanese, ‘iki’ is an aesthetic ideal, an expression of simplicity, sophistication and spontaneity. Iki tsu means knowing how to eat and appreciate seafood. Iki jime is the simple dispatch of fish by a means that allows iki tsu.
The idea is to instantly kill the hind part of the brain, where movement control is centred. This is the method the Japanese use universally across all species: Poke a sharp spike inserted towards the head at a 45degree angle at the intersection of an imaginary line drawn horizontally across the top of the eye, where it intersects with an imaginary line drawn vertically against the inner end of the jawbone. In most fish, including snapper, this is about 2cm back and up from the eyes. Push forwards and down towards the spot in the middle of the eyes.
If you’ve done it properly the fins will flare out for two or three seconds before the heart stops pumping and then they will relax. Colour will return to the fish almost immediately. If it is still moving you missed, because the brain-dead fish cannot instruct its muscles to move.
The great advantage of iki jime is that this instant kill results in the blood retracting into the gut cavity. The less blood in the flesh the better, as blood taints the fillets with bitterness and it also encourages decomposition, so fillets will not last as long in the fridge. And the sooner a fish is cleaned the better; the bloodline along the backbone is the equivalent of human kidneys.
Eric Barratt who is manager of commercial fishing company Sanford Ltd agreed that iki jime became the standard practice for the industry because the Japanese market demanded it. Sanford did not do its own research to verify the Japanese belief but had taken note of overseas studies. “It’s still seen as the best way of processing (fish), it is technically the best way of preserving the flesh,” Barratt said.
Much of the fish that is caught commercially is taken by net and is dead when hauled onto the deck, so iki jime applies mainly to the snapper caught on long-lines.
In the United States, scientists tested the iki jime method against other means of dispatching farmed Chinook salmon. They measured muscle relaxation via an “isometric rigormeter” which showed the extent to which rigor mortis had affected the fish flesh and determined that it was better than cutting the bloodlines under the gill plate or removing the head altogether as well as making a cut across the tail.
One of the major reasons was because there was less flesh bruising. But they noted that the restaurant trade in particular wanted access to whole fish and that there was buyer resistance from both restaurateurs and their customers when whole fish had a spike mark through the head. In some cooking methods, the area around the spiking showed a different colour when served, adding to eaters’ unease.
Keeping fish in an ice slurry is a perfect way of keeping fish fresh.
Peter Thornley is the top man at Auckland’s renowned seafood haven Kermadec near the Viaduct Basin, a restaurant with a reputation for serving the best fish available. Referred to by the Kermadec cooks as “Chef,” Thornley is the only chef outside of Europe to have won the Mandarin Napoleon Culinary Grand Prix and was named Singapore’s “Chef of the Year” for four years in succession. His is a familiar face on TVs cooking shows, including Ready Steady Cook, the Good Living Show and MasterChef. So he knows good fish when he sees it, as well as bad fish.
“There is no doubt the iki method does make a difference to keep commercially caught fish flesh in better condition,” he told NZ Fishing World. But as an occasional saltwater fisherman himself, it is not the method he uses when hooking snapper in the Hauraki Gulf.
He had just come back from such a trip when this interview took place. “I hooked a really big one (snapper) right at the end and lost my rod over the side,” he admitted ruefully. But they already had some on board and iced down. “We set up a slurry that’s really cold and simply put the fish into it as quickly as possible.” And when you get home it should be filleted ASAP to prevent the gills and gut tainting the flesh.
“You can tell the difference when fish is treated this way - there is a marked difference from any fish that you can buy, it simply tastes better. Of course it doesn’t come any fresher than when you catch yourself,” Thornley said. “If you do not deal with fish quickly after it is caught it will develop a fatty, meaty taste. It is critical to get the fatty muscle out.” That applies particularly to the more bloody fish such as kingfish and tuna, he said.
When sourcing fish for the restaurant he has a set of standards that help him determine what to buy and what to pass on, based on appearance of the flesh, and of the fillet, as well as smell. Good fish glistens. It smells of the sea.
Fish from deeper, colder water is always better than those caught in shallower, warmer temperatures,” he said. “The further south you go in New Zealand the better the fish gets.”
Thornley made comment on New Zealanders’ fish preference, urging people to look beyond the snapper and John dory that is standard in most restaurants.“If we put gurnard on the menu no one will touch it, they’ve seen it in the supermarkets and they go ‘we’re not eating that.’” He buys fresh hake from Kaikoura. He’d like to see species including alfonsino and ruby on menus, and more blue cod. The new menu at Kermadec even features a pilchard dish.
“New Zealanders need educating about fish other than snapper. The trouble is some chefs don’t understand how to cook these species.”
Personally, I believe the slurry method delivers a better fillet to the table. And it is better than just putting the fish on ice, including salt ice.
The science also shows that partially freezing fish flesh encourages decomposition. Salt ice can make a slurry down to between -1degreeC and -6degreesC, which will partially freeze the flesh.
So the best idea is to pour seawater into the chilly bin to about one-third full then throw in chunks of freshwater ice or salt ice. Even better, freeze old milk bottles full of tap water and use these to cool the seawater - the fresh water doesn’t mix with the salt. As fish numbers accumulate, pack them in upright so juice from the gut is not running into the body.
When filleting, take care not to get guts on the flesh as this also encourages spoiling.
With some fish it is simply easier to put a sharp knife through the gill plate and cut the throat e.g. kahawai. As the heart pumps its last beats the blood is ejected. With blue cod, you can cut that line then break the neck - as instant a kill as iki jime.