Japanese Fish-Killing: Ike Jime Smackdown Part 2

posted by Dave Arnold

The Results:

If you don’t know Ike Jime, read our Ike Jime saga in Ike Jime Part 1 here.

When we left off, Chef Suzuki had sashimied up a bunch of fish for us to taste. Unfortunately, the fish was really too fresh. The oldest fish in the bunch had been dead only 4 hours and the youngest only 2 (all fish of the same type had been killed at the same time). Ideally, we would have waited at least a day to cut the fish. After death, rigor mortis sets in and the muscles tense up. They don’t relax quickly. Some fish, like salmon, are kept several days before eating so that rigor can “resolve” itself (that’s what the meat scientists say—resolve). More on rigor mortis later. Even though the tasting wasn’t going to be ideal we were hoping to see differences between the techniques. We couldn’t wait till the next day because we wouldn’t have chef Suzuki the next day.

Watching Suzuki cut the fish was a pleasure. On many of his slices he would make an extra—almost invisible—cut meant to absorb soy sauce. Nice stuff.

Here is what we had:
Small farmed striped bass (all 4 hours dead): Western (no bleeding, left on counter for 20 minutes, hit on head, gutted an hour later), Japanese bled (cut through the spinal cord behind the gills and at the tail and bled in ice water, then gutted right away), and Ike Jime (like Japanese bled but with a needle jammed into the spinal cord.)
Small fluke (all 2.5 hours dead): Western (no bleeding, but hit on the head right after removing from water, gutted an hour later), Japanese bled, and Ike Jime.
Small black sea bass (2 hours dead): Western (like fluke), Japanese bled, Ike Jime (the Ike Jime on this was only partial, it was hard to get the needle all the way down because the spinal cord was so small).
Barramundi: Not tasted (we were going to cook it next day)

We tasted them blind first, and then continued tasting after we knew which was which.

The difference between the stripers was amazing. The un-bled striper’s flesh was obviously ruddy, had a metallic flavor and a mealy texture. The Japanese-bled fish was very clean tasting and didn’t have the mealy texture of the un-bled fish. It was good. The Ike Jime striper, however, clearly had a firmer, better texture. 100% of those present preferred it. If you look at the picture, you can see that the Ike Jime striper has more color than the Japanese-bled. I think this is because it took a while to get the needle in whereas the other fish went right into the ice water to bleed. An alternate explanation is that Ike Jime lessened the force of muscle contractions, and strong muscle contractions help expel blood. In the future, I will place the fish in water to bleed first and then needle it. As an interesting side note, the Ike Jime striper, even after 4 hours, even after it had been gutted, was still twitching occasionally—the muscles were still “alive” as Suzuki said (technically, the ATP, adenosine triphosphate, hadn’t been fully used, and that is the critical issue with Ike Jime as we shall see later).

The Western Fluke didn’t look as bloody as the striper, but the texture was mealy mealy mealy. I had to spit out a part of it, while other parts of the fish were not as bad (I wish I had written down which part of the fish had the worst texture). The Japanese-bled was clean with a good texture (for a freshly killed fish). The Ike Jime fluke was crunchy—like seaweed. Really amazing difference. I don’t think you’d want to serve it that crunchy, but it was good. The theory is that the rigor in the Ike Jime fish will resolve into a better texture the next day.

The black sea bass had the least difference between the types. It also had the least time between the kill and the taste, for whatever that’s worth. The un-bled bass wasn’t bad—a little mealy. We didn’t get any metallic taste. The differences between the Japanese-bled and the Ike Jime were not as great as with the other fish. This could be because of partial Ike Jime, or because we didn’t wait long enough, or because the black bass doesn’t need the needle. More experiments are needed.

Clearly, the Ike Jime was doing something. I needed to figure it out.

That night, I happened to have a neurobiologist-doctor friend over for dinner. Bob Datta is an MD PhD who is also a food nut. Every year, instead of a birthday party, he throws an “I’m Still Alive” dinner to commemorate the anniversary of his bone marrow transplant. The dinners are legendary. Anyway, he is moving from Columbia to Harvard (he is a real dummy), so I had him over before he left. When I told him about Ike Jime, his first response was “that sounds like bullshit, after you sever the spine what more do you need to do?” So I pulled out my favorite talking-to-a-scientist line: Empirically, there appears to be a difference, so assuming it isn’t bullshit, can you think of a plausible theory for why Ike Jime could make a difference? This question produced the desired state of deep-thinking in Dr. Datta. About 30 seconds later he said “central pattern generators.” What? “CPGs.” What? “Central pattern generators are groups of neurons that contain within them the coding for complete behavioral patterns, like the swimming motion in fish. They don’t require a connection to the brain to work. In fact, the brain inhibits them. When left on their own they want to fire. Killing the brain wouldn’t knock them out.” Bang. I had a plausible theory. I called McGee. He also thought it was an interesting theory.

Then I hit the science databases to look for papers on the subject. I ended up reading about 20. Here’s what I learned:

Many, many people are concerned with the development of rigor mortis in fish. When a fish is killed it still has ATP (adenosine triphosphate) in the muscles. ATP is the energy source that makes muscles (and everything in any living creature) run. It takes ATP to contract muscles, but it also takes ATP to relax muscles. As the ATP starts to run out, the muscle loses its ability to relax, so every little contraction becomes permanently set. The muscle only loosens up again because the muscle proteins themselves get degraded by enzymes and decomposition. The feeling with scientists is that the faster rigor happens, the harder it happens, and the lower the quality in the final product after rigor is resolved. Fast, hard rigor produces fillets with looser flesh, more drip loss, poorer color—you name it. There are many papers on how to delay rigor in fish by preventing struggle and stopping premature ATP depletion (chilling, anesthesia, slaughter technique, etc). Aside from depleting ATP, when muscle activity goes up during the death struggle, lactic acid is produced in the muscle which lowers pH which also supposedly affects quality by lowering water holding capacity (although some current research says pH isn’t as important in fish as it is in mammal meat). A third issue with fish slaughter is that when the fish is frightened or struggling, it releases compounds into the bloodstream which might affect quality. So how does Ike Jime work?

SPINAL CORD DESTRUCTION!

The best paper on the subject I could get my hands on is: Influence of storage temperatures and killing procedures on post-mortem changes in the muscle of horse mackerel caught near Nagasaki Prefecture, Japan, Toshio Mishima, et al. in Fisheries Science, 2005; 71: 187-194 (I can’t post a link because you need an account that can log into the Science Direct database. All you university types can get it. If anyone can get a hold of the Fisheries Science journal number 62 from 1996, there are 3 articles I want to read that are referenced in this article). The technique we have been calling Ike Jime they call “spinal cord destruction (SCD).” I like that—very descriptive. “The fish were killed by making a cut at the brain, letting it bleed, and immediately destroying its spinal cord by the insertion of a piano wire through the neural canal.” Here is the story: Certain fish that swim for very long periods have highly a highly developed autonomic nervous system for swimming (sounds like the CPG’s Bob was talking about). These fish, like bass, like horse mackerel, etc. benefit from spinal cord destruction. Other fish, like plaice, that don’t have highly evolved constant swimming reflexes, don’t benefit (or at least not as much). The paper recommends doing a species by species test to see which fish benefit the most. The paper didn’t mention CPG’s (in fact no paper did that I could find). Someone needs to do some research on that. So then, when you destroy the spinal cord, you destroy the swim reflex, which helps reduce ATP loss, delaying and softening rigor, increasing the quality of the fish. Another interesting point in the paper is that we are probably storing our fish too cold. According to them, fish should be held at 10ºC for 24 hours after slaughter for maximum quality. Voila. Almost.

There is another interesting paper that raises some questions: Pre- or post-mortem muscle activity in Atlantic salmon (Salmo salar). The effect on rigor mortis and the physical properties of flesh, by Bjørn Roth, et al in Aquaculture 257 (2006) 504-510. These scientists killed “rested” salmon by whacking them over the head and then put electrodes in the brain to stimulate muscle movement. They artificially contracted the muscles until all the ATP had been used up. The fish went into rigor very quickly—more quickly, in fact, than similar salmon that they had “stressed” before they killed and much more quickly than salmon that had been “rested” and killed. The electro-stimulated fish also came out of rigor quicker than the other salmon. Here is the interesting part: The quality of the electro-salmon was judged the same as the rested one. The stressed fish were not as good. These authors point out that early rigor alone isn’t what decreases quality. There is some other mechanism involved. They speculate that the absolute force involved in the muscle contractions is higher in stressed and panicked fish and THAT is what cause post rigor texture to be affected. Their electro-stimulation they say, was more gentle on the muscles than the brain of a fully frightened fish.