IKEJIME the method of killing a fish
Ikejime (活け締め)
Ikejime (活け締め) is a method of killing a fish while preserving the quality of the fish meat.
Therefore, ikejime is a fish-killing technique used in Japanese fisheries for over a thousand years. Fish are caught with a hook and a sharp iron rod is inserted into the brain in the head to instantly kill the fish. A sharp wire is then inserted into the spinal cord through the tail fin to depress the nervous system, preventing the fish from struggling, which can reduce the quality of the meat.
Next, the fish's blood is drained through the gills, where the arteries have been severed, and it is quickly refrigerated to prevent bacterial growth. This process must be performed by experienced and skilled fishers who understand the fish's anatomy to avoid mistakes that could cause distress to the fish and degrade the quality of the fish meat.
Ikejime and Fish-Blood Draining
To preserve fish meat quality, the fish must be prepared gently, preventing excessive struggling or suffering (when the fish struggles, the meat temperature rises and lactic acid is released). (acid) + carbonic acid (carbonic acid) increases until the blood becomes acidic, which reduces the quality of the meat.) In addition to gently catching the fish so as not to startle them, you can also use other methods, such as adding ice to the fish tank, waiting 4-5 minutes until the fish is relatively still, but the fish is not dead yet. Gently place it on a cutting board, then follow these steps:
1. Use a steel rod to stab the fish's brain, which is located at the base of the gills, slightly above the spine (see picture). You can stab from the front or the side to kill the fish immediately. The heart stops pumping blood.
2. Drain the blood as quickly as possible by cutting the arteries carrying blood from the heart to the gills and the arteries from the gills to the brain. Wait for the blood to drain through the gills until the fish is relatively still. Lift the fish's tail to allow as much blood as possible to drain through the gills.
3. Cut at the base of the tail, severing the vertebral column to expose the spinal cord nerve canal (close to the upper vertebral column) and the artery canal (close to the lower vertebral column; see image in step 3).
4. Insert a wire into the spinal cord nerve canal to stop the fish from thrashing around and reduce acidity in the blood after the heart stops beating, in order to preserve the quality of the fish meat as much as possible. (In addition to the wire method, a high-pressure water jet can be used to push the nerves out through the hole drilled in the head.)
During the fish preparation process, blood must be drained because the blood does not carry oxygen and nutrients to the cells when the heart stops beating. The blood becomes acidic and becomes a breeding ground for bacteria, ruining the fish meat.
5. Use a low-pressure nozzle to gradually inject water into the arteries through the base of the tail (as cut in step 2)* (or use a syringe to inject a solution to reduce blood acidity, approximately 10%-15% of the fish's body weight, into the blood vessels to flush out the blood). Observe the fish's body; it will tense up as water is injected into the bloodstream. Lift the fish's tail to allow as much blood as possible to be drained through the gills. Repeat this process several times to maximize blood drainage.
6. Wash the fish thoroughly. Remove the scales (or leave them on), cut open the belly, and remove the gills and innards.
7. Use a high-pressure water jet to spray water into the blood vessel opening at the base of the tail that was cut, until the fluid flowing from the gills is clear. The more blood is drained, the less fishy odor the meat will have.
8. Use a high-pressure water jet to spray water into the spinal cord nerve opening at the base of the tail that was cut. Wash again and dry thoroughly.
Store the fish in a vacuum-sealed bag and freeze for a period depending on the size and type of fish (possibly up to 10-14 days) to maximize adenosine content. This will result in better flavor and less foam in the broth when cooked.
*Do not use high-pressure water jets to spray large amounts of water into the blood vessels, as this can cause internal organs to protrude through the gill openings or rupture, contaminating the fish's abdominal cavity.
The Origin of Adenosine - The Origin of Umami
The primary purpose of ikejime (Ikejime) in fish is to slowly stop cellular respiration after the fish dies, resulting in high-quality, delicious umami meat. A byproduct is fresh, clean fish meat that can be stored for a long time, thanks to the cleansing of the fish's blood.
When fish are alive, they undergo the following energy-taking and utilization processes: When fish consume food containing the three main energy-producing nutrients: protein, carbohydrates, and fat,1 their digestive system breaks these nutrients down into amino acids, sugars, and fatty acids, respectively, in the stomach and intestines. These nutrients are then absorbed into the bloodstream. Blood containing these nutrients is pumped to the heart and pumped through the heart through the gills to obtain oxygen. The blood (now containing nutrients and oxygen) then flows through the spinal arteries2 and the arteries supplying the brain. Cells receive nutrients and oxygen from the blood. Mitochondria in cells synthesize energy from nutrients and oxygen, converting adenosine diphosphate (ADP) to adenosine triphosphate (ATP), which is stored for use in cellular energy. During cellular respiration, ADP is broken down to provide energy, which is then converted back to adenosine diphosphate (ADP) + phosphate. While fish are alive, their cells receive nutrients and oxygen from the blood, allowing ADP to be synthesized back into ATP for storage and reuse. This cycle continues throughout the fish's life.
When a fish dies, its heart stops beating, and nutrients and oxygen are no longer transported to the cells. However, the cells still require energy. Therefore, a metabolic process occurs without oxygen. The cells begin to break down ADP into energy + adenosine monophosphate (AMP) + phosphate. Subsequently, the cells break down AMP into energy + phosphate + adenosine (adenine + sugar). Adenosine is the substance responsible for the delicious taste (umami). Fish can take 10-14 days, depending on the type and size, while beef can take up to 28 days to fully develop adenosine.
1. Nutrients include: 1.1 There are three main types of nutrients: protein, carbohydrates, and fat. 1.2 Other compounds include vitamins, minerals, and others. For example, shrimp contains 24% protein, 0.2% carbohydrates, and 0.3% fat, with the remainder being salt, cholesterol, vitamins, dietary fiber, etc. Similarly, roasted seaweed contains 20% protein, 20% carbohydrates, and 40% fat, with the remainder being salt, cholesterol, vitamins, dietary fiber, etc.
2. The arteries in the spine carry blood containing nutrients and oxygen to the cells of the body.
3. Cellular respiration is the process by which cells metabolize nutrients and oxygen to produce energy. In cases of cardiac arrest, cells begin to metabolize food without oxygen, resulting in lactic acid and carbonic acid, or acidosis.
