Sashimi or “Otsukuri”, in the Kansai region of Japan, is fish eaten in a raw or almost raw state. The preparations for Sashimi are often simply butchering and slicing. The minute details that get lost in the cooking process come to the foreground when you are eating fish raw.
After a fish dies, a whole bunch of physical and chemical changes start to affect the flavor and texture of the flesh. The most important of these processes is the softening of connective tissues. A bunch of enzymes in the fish start to break down the muscle fibers and proteins rendering the once resilient flesh limp and fragile. Think about the difference between a live salmon fighting on the end of your fishing line compared to the flaccid supermarket salmon filet that you could poke your finger through. Most fish that we eat in the west has effectively been decomposed by the time it gets to us.
The language I’m using is more science-y then food-y, I’m sorry in advance if most of this is gross and unsettling. We need to think of this technically so that we can preserve the delicious textures of fresh fish and make a better meal.
The biggest factor in the softening of the flesh is time. The longer you wait after the fish has been killed, generally the softer the flesh. For some fish this aging process can be wonderfully delicious. As the proteins break down, umami begins to develop. Some fish can be aged just like beef to produce rich savory flavors.
“Shiromi” white-fleshed fish generally are not great to age as the texture becomes unpleasantly mealy. For these fish such as bass, bream, and flatfishes, the firm elastic nature of their live flesh is what we are going for. Though the breakdown of the muscle fibers and loss of texture is inevitable, there are a few ways to delay it.
There is a window of time between when the fish is dead but before cells in the muscles have died. Just the same way a chicken can run without its head, it takes some time for the muscles of the fish to shut down. This can take between a few minutes and a couple hours if we use standard slaughtering practices before rigor mortis sets in and the muscles die. With Ikejime this window of time before the muscles break down can be prolonged up to a day or sometimes even longer. It is not indefinite but it does buy you some time to get the fish to the guest or the dinner table. For most fish, the day after Ikejime, the flesh will seize up and begin to break down.
(I will go deeper into the decomposition in future posts so that we can understand storage and aging of fish a little better)
Ikejime is a general term used to describe a variety of techniques that delay the onset of rigor mortis. Rigor mortis seems to kick in once the cells in the muscles run out of ATP (Adenosine Triphosphate) which acts like the fuel in the tank of a car. The muscles use this energy up when they flex or contract. Quickly after the brain has died, the nervous system of the fish triggers seizures in the muscles which quickly deplete all the ATP. The muscle cells die, decompose and loose their wonderfully elastic texture.
To prevent these seizures, we have to destroy the nervous system of the fish. The best way to do this is to destroy or remove the part of the brain that sends these signals, and the spinal cord that passes the message to the muscles.
The brain of the fish can be handled in one of two ways, either by inserting a knife or awl into it, or by cutting through the spinal cord that connects it to the rest of the fish. After this the fish is dead but we still have to address the spinal cord. A wire can be inserted either from the previous hole in the head, a cut at the end of the tail or in some cases through the nose of the fish. The idea is to damage the spinal cord as much as possible, or remove it completely using the wire. High pressure water pumped through a needle can also be used for similar results.
There are finer points and details that vary from fish to fish, but this is the general idea of the technique.
We are talking about the nervous system of the fish and how to prevent these self-destructive messages by the brain from making their way to the body. There is an equally important part of Ikejime that addresses the circulatory system of the fish. By doing Ikejime properly, we not only prolong the elastic texture of the fish, but we can drastically reduce the amount of blood left in the muscles of the fish. So what’s wrong with the blood?
While the fish is alive, blood brings energy to the muscles in the form of oxygen and glucose. Once the fish has died, that energy is an all-you-can-eat buffet for bacteria. Leftover blood in the flesh will soon rot and give off that all-too well known old-fish-smell. With Ikejime we can drain the blood out of muscles and into a reservoir just under the spine called the hemal canal. (I’m not sure why this takes place, please tell me if you understand this process.) This can be easily removed when we clean and gut the fish. When it comes to ageing, cleaning out as much blood as possibles crucial. There is a very fine line between aged fish and old fish. Less blood = less smell.
The best way to get rid of the blood is with lots of water. Unfortunately however, water getting into the flesh of the fish quickly triggers rigor mortis. Darn. By cutting the gills of the fish and/or the base of the spine by the tail, blood can be quickly pumped out. Just like the brain and spinal cord, there are dozens of ways to get the blood out depending again on species and desired results.
Hopefully with a little more research and practice you have got the hang of Shinkenuki/Ikejime. Your fish has a lovely firm texture and not a drop of blood in sight. Let’s keep it like that for a long as possible...easier said than done. That ATP, that is keeping the muscles alive and postponing rigor mortis, is running out and there is no way to replenish it once the fish has stopped eating and breathing. Here are the things that we need to avoid in order to keep the muscle alive as long as possible. Heat. Cold. Dry. Wet. Cold temperatures will stop the cells from using the ATP even if there is plenty still left. 5 degrees Celsius seems to be the best for storage. Putting Ikejime fish in a normal refrigerator will quickly onset
Ikejime is a way to kill the fish at once without stressing it, Japanese fishermen, butchers and chefs do it when killing the fish for dish need flesh meat such as Sushi or Sashimi, or for fine dining restaurant. This technic couldn’t find many at the USA and Canada where I worked, but it changed taste and texture huge different for white fish.
Shinkei-Nuki is the technic some people do for some specific fish after Ikejime by driving a spike directly into the hindbrain. You can see on the video there is a hole left, it from Shinkei-Nuki.
On the video, we used some Japanese words, here are the translations:
Shiromi = Whitefish
Hirame = Flounder
Hamo = Pike conger eel
Tai = Sea Bream
Ako = Pacific ocean perch
Hata = Grouper
Katsuo = Bonito
Buri = Yellowtail
Most of the Japanese fine dining using fish that killed with Ikejime and Shinkeinuki sometimes. But if you eat a fish at a supermarket store, often time they didn't kill the fish with this technic.
This article was written by Jon Klip. Please visit here to see his recent work on Instagram.