My japanese girlfriend dont believe me when I say that most....say 90% of the maguro in Japan has been frozen at some point before you get it to eat ..... she watched something on Nippon tv and they said that there is unfrozen maguro available.... well where is that ? Ive caught Tuna [not off japan], and it needs freezing to kill bacteria and makes the meat better to eat .. otherwise ..straight after catching a Tuna ....day 1 meat is crunchy ..yes cruchy.!! day 2, softer texture , day 3 is perfect .. I believe that all tuna has some frozen time..lets face it they are caught way out to sea and are put straight into ice slurry after the ikijimi death spike.... please tell me otherwise ..I cant see anywhere online about how much is frozen ...too much wording abiguieties.. like the word "fresh "... still might imply its been snap frozen .. have you ever seen Tsukiji fish markets in Tokyo where they deal with frozen tuna daily ??? hmmmm I need to hear your facts ..cheers
Regarding frozen maguro, yes, most of it has been frozen. All the farmed maguro is delivered frozen, and that is perhaps half of what is sold at Tsukiji every day (it comes mostly from Australia or Viet Nam). Most of the caught Indo maguro (from the Indian Ocean) as well has been frozen. A friend of mine's shop has a sign posted saying none of the fish served has been frozen with the exception of maguro. If you want maguro that has not been frozen I suggest finding some from Oma, in Aomori Prefecture. If you visit Tsukiji jonai, the wholesale market, you will see a lot of shops cutting tuna with bandsaws.
Regarding Asomaniac's comments regarding aging maguro, that is true. Maguro is the only warm blooded fish and so like beef, is best when aged for a week or so; the fish needs time for certain amino acids to develop as muscle fiber proteins breakdown. Otherwise it would be very tough and lacking in fully developed flavors.
As for the comment regarding finding gutted and headless tuna at Tsukiji, no way. All maguro are auctioned whole, the exception being that the tail has been cut off. Perhaps he was thinking of the Honolulu wholesale fish market where fish are displayed for auction opened up, but not Tsukiji. That is why there is the "Tuna Court," a place where disputes regarding large fish (maguro and kajiki) with serious defects can be resolved.
The frozen tuna auction is bigger than the fresh tuna auction at tsukiji, but both are big. There is fresh tuna there from all over the world. The fresh auction is more than 10% of all the tuna sold at auction at Tsukiji, but I imagine that for all of Japan the large majority of bluefin tuna is frozen. You can see the sales figures somewhere on the Tsukiji website. Tuna does not need to be frozen for any reason. Freezing doesn't kill bacteria, and there are no dangerous parasites in tuna like there are in freshwater fish. Tuna is sold gutted with the head on.
I have fished for tuna (bluefin/bigeye/yellowfin/albacore) commercially and recreationally.
I felt bluefin was best at 5 days plus.
You are correct regarding spiking and ice bath, this is to prevent scromboid (histamine) poisoning. When I was albacore fishing, we had to plant temperature recorders in the fish's body, this was a requirement of our buyer. Our refigerated saltwater was around 30 degrees F. We had to chill the albacore below 40 degrees F within a couple of hours and the temperature had to stay below 40 until delivered. I don't remember the exact time requirement, but I remember 40 degrees.
We were usually only a day or two from port when fishing albacore, but when fishing the other tunas, we could be at sea for weeks. All of the other tunas were frozen solid. Because of logistics, I think any fresh (never frozen) bluefin would come from a pen or from the Mediterranean Sea, served locally.
There are recreational fishermen out of San Diego who fish with refigerated salt water, their rule is any tuna caught 5 (or 6?) days from port go into the RSW, all other tuna are frozen solid.
No parasites or bacteria that I knew of, just the histamines.
On one trip, I got to see the bluefin pens in the eastern pacific, we watched them feed and harvest tuna. Divers in wetsuits wrestle the tuna, selecting specific ones based on size. On that trip, we had a tuna buyer, he took an ~80lb bluefin, cut it up, and each day he had a platter for us to try. I agree, first couple of days, it is crunchy, also the sweet (to me) taste doesn't develop for a couple of days. That trip we were fishing ~200 miles offshore, ~400-500 miles south of San Diego CA. I have eaten fresh albacore that was 14 days dead, but kept at ~32 degrees, similar to beef, the flavor/texture changes as the fish ages.
I have also worked in Alaska, processing IQF (individually quick frozen). Best halibut I have every eaten. The company I worked for was trying to get consumers to buy vacuum packed IQF, but it seemed that a consumer in "Iowa" would buy frozen beef but not frozen IQF, the stores would defrost the fish and sell it that way, reducing its self life. Too many media chefs with fresh fish available trying to convince people who don't have fresh fish available that frozen is "bad".
I understand your interrogations about frozen maguro. The Japanese fishery industry is one of the most technically advanced - especially concerning manipulation of 'maguro'. I learn recently that after being fished 'ippon zukuri', on some boats, maguro are put in an ion water to avoid stress, ..
Actually, it seems that only small fishing boat, fishing maguro near the Japan coast, fish 'nama(fresh)' maguro ; and so their size will be smaller as the boat can't go far... and so the fish wont be so fatty, as it will typically weight like 70 to 150 kg. Some nama maguro are sold in the supermarkets and referenced as 'nama', they are the one to choose !! Usually the supermarkets don't have the equipment to freeze maguro at -60° as is necessary ... so you can find quite easily some nama maguro. For ex. just go to Okachimachi, at Matsuzakaya's basement, there you will easily see some nama. Also, you have sushi-yasan that use it, the chutoro will be more red colored, but very good in fact, that bloody flesh nice perfume can be smelled while eating.
Some farmed ones are frozen, and also some 'ippon zukuri' are too, but if the duration of freezing is very short, and at temperatures under 60°, so it should be OK. After thaw out, it is up to the ushi-yasan to managed to the aging - at least the good ones do it. I understood for ex. some sushi-yasan, like Sukiyabashi Jiro, have specific fridge with different part for different fish (at least the ones that are very expensive, typically like maguro).
In Japan in general, maguro is sashimi, sashimi must be grade up, and are usually expensive, and the sashimi have to be colored red ! In minus 20 degree, it will change color, it is not decomposing or changing in nutrition, the red color comes from myoglobin and gets brown if not adequete
and as 'maguro' is soft importance is that defrost it it will drip, flavor also.. it is why some supermarket put some paper to absorb.. After also it depends of the water contained of the fish, the flesh the more fat it contains the more difficult it will be, for exemple the 'boston maguro' was referred as 'shibi(4days)', as it used to be necessary to age it at least 4 days to eat it, due to the fat contained, but in good sushi-yasan the fattier parts can be hold to 5-10 days..
Concerning the import of maguro, the link here below shows that in 2007, imports line(in red) decreased, but volume if fishing around the coast was maintained, so the estimation is around half Japanese marekt is importation... but it depends very radically on the type of maguro