The Story of Sushi: An Unlikely Saga of Raw Fish and Rice

by Trevor Corson

  Zoran handed the two halves of the siphon to the students, one half for each side of the table. The students practiced making sushi with the clam. Kate sliced off two pieces and passed it on.

  “Who likes mirugai?” Zoran asked. Only a few of the students raised their hands. “Wow, that’s it?” Zoran said. “Tsukiji Fish Market, 6:00 a.m., a meal of beer and mirugai—so good! But you must tenderize it. If you don’t, you’re going to be chewing like a cow.”

  Zoran eyed the students. “C’mon, taste the mirugai if you haven’t yet. I don’t care if you spit it out. If you’re going to be at the sushi bar, you should know what taste you’re shooting for.”

  Kate had no interest in eating an undulating clam that looked like a penis, but under Zoran’s eye she sliced a tiny corner off one of her nigiri. It felt like chewing on a rubber band. Zoran watched her. She knew he was waiting for her to spit it out. She swallowed.

  39

  FINAL FISH

  The last day of Zoran’s marathon of fish lessons dawned crisp and clear. A fresh ocean breeze blew in from the Pacific.

  Today the class had arrived at the culmination of contemporary sushi. The Japanese had long disparaged the fish for today’s lesson as poor man’s food—a gezakana, or “inferior fish.” Even North Americans had been known to discard trophy-winning specimens of this fish at the town dump because no one would eat it.

  But now the fish’s status in Japan has risen to kokyu sakana—“high-class fish.” North Americans fall over themselves to sell the best specimens to Japan and then buy them back at astronomical prices. At which point, they fall over themselves again to eat them.

  “Somebody tell me a type of tuna,” Zoran said. He wrote the Japanese word for tuna—maguro—on the whiteboard.

  “Bluefin,” the students called out. “Bigeye.” “Yellowfin.” Zoran nodded. Sushi chefs serve all three, but bluefin is king.

  A bluefin tuna can grow to weigh 1,500 pounds. Bluefin inhabit cold waters and their bodies can be up to 15 percent fat, depending on the region and season. Bigeye are smaller, and live in temperate and tropical waters. Yet they swim deep, where the water is relatively chilly, and thus can accumulate up to 8 percent fat. Yellowfin tuna are about the same size as bigeye. They inhabit warmer waters, and accumulate only about 2 percent fat.

  “There’s different types of maguro meat,” Zoran said. He wrote the English names on the whiteboard, with their Japanese counterparts:

  red meat—akami

  medium fatty—chutoro

  fatty—toro

  very fatty—otoro

  Toro got its name from “torokeru,” the Japanese word to describe something melting. The chu in chutoro means “middle,” and the o in otoro means “very.”

  Apart from the question of fat, all tuna flesh is red meat. Although some tuna have shiny skin, sushi chefs categorize them as red fish. Bluefin in particular are the reddest. They are also the fastest fish in the sea.

  Bluefin tuna appeared in the ocean as recently as 1 or 2 million years ago. For a fish, their circulatory systems have attained a new level of complexity and sophistication. Like mammals and birds, bluefin are warm-blooded. Warm-blooded creatures routinely move and react faster because crucial chemical reactions in the body can occur more quickly in a heated environment. This is especially valuable to a predator.

  In the cold waters of the ocean, however, retaining body heat is a challenge. Most of the warmth a fish could generate inside its body would be lost when the blood is exposed to the cold water, as the blood passes through the fish’s gills to collect oxygen. As a result, most of the fish in the sea have remained cold-blooded.

  To become warm-blooded, bluefin developed an elaborate counter-current heat exchanger inside their bodies. As warm blood leaves the bluefin’s muscles and heads for the gills to pick up more oxygen, the veins it travels through run directly alongside the veins carrying the colder blood returning from the gills. The cold blood absorbs most of the heat from the warm blood and carries the warmth back into the body. By the time the low-oxygen blood arrives at the gills, it’s already cold. The bluefin’s heat exchanger is so efficient that it retains 97 percent of the animal’s heat.

  Bluefin tuna can swim faster, see better, digest more food, and react more quickly than other fish. Scientists estimate that bluefin can swim at speeds of 50 miles an hour. But there’s a price. They can cruise at a more leisurely pace, but they must always swim fast enough to ensure a sufficient flow of oxygen across their gills to fuel their system. If they swim too slowly, they will suffocate.

  For bluefin, the distinction between fast-twitch muscle and slow-twitch muscle is largely irrelevant. Instead of having a thin ribbon of slow-twitch muscle that runs down each side of the fish under the skin, the bluefin’s slow-twitch muscles have migrated inward—where they will stay warm—and have swelled into massive, high-output engines that produce fast-twitch performance.

  And unlike most fish, which flex their spines when they swim, tuna remain stiff, directing 90 percent of the thrust their engines generate into the movement of the tail fin alone, rather like a torpedo. The stiffness of the swimming tuna is so well known in Japan that the word maguro is used to describe a woman who is stiff during sex.

  Bluefin hunt in packs like wolves, in formation. When they locate a school of small fish or squid, fifteen or so bluefin attack together at high speed in a parabola, shaped like a mouth. The parabolic formation acts as a dragnet to concentrate the prey, but it also allows the bluefin to attain higher speeds as they push off each other’s wakes.

  To supply the vast quantities of oxygen necessary to fuel the bluefin’s massive engines, the tuna pumps its muscles and blood full of myoglobin, the iron-red protein that transports oxygen. That’s why tuna meat is so red.

  When prey are abundant, bluefin store up fat for future use. Fatty cuts of bluefin—toro—became a popular sushi topping in Japan beginning in the late 1950s. Sushi chefs cut the highest-grade otoro from the forward section of the bluefin’s belly. otoro can be as much as 40 percent fat. Sushi chefs distinguish two types of otoro. Jabara—literally, “snake’s stomach”—is the fattiest part, and comes from the bottom of the belly. Shimofuri—which means “fallen frost” and can refer to any red meat marbled with fat—is rarer, and comes from the upper belly.

  “Now, toro doesn’t just mean from the belly,” Zoran said. “You can get toro from other parts of the fish.” He drew a diagram on the board.

  Sushi chefs cut the mid-grade fatty cuts, chutoro, from the rear and upper sections of the belly, but also from the upper and outer portions of the back. This meat is 15 to 20 percent fat.

  Toward the center of the fish, insulated by the fat, resides the akami, or red meat, the primary engine that continuously drives the fish through the water. Chefs find that the best-tasting akami lies between halfway and two-thirds of the way to the tail. Here, the muscle gets more exercise than the muscle toward the head, but contains less fiber than the muscle at the tail.

  Hard-core sushi aficionados will still choose a good piece of red meat over toro. They consider the fattiness of toro to be too simplistic a pleasure. By contrast, appreciating a fine cut of akami takes experience.

  Either way, getting a fine cut of tuna from the sea to the sushi bar isn’t a simple matter.

  “Ninety percent of tuna,” Zoran said, “when they catch it, they bleed it, take the head off, and flash-freeze it.”

  Like salmon, much of the tuna at the sushi bar has been frozen, but with more elaborate technology—even when sushi chefs say it is fresh.

  Regular freezing inhibits bacteria, which is good, but it creates other problems, particularly in the form of ice. During regular freezing, the water in animal flesh migrates out of the cells and forms ice crystals between them. Since water expands when its molecules rearrange themselves into ice, crystallization can crush nearby cell structures, turning the flesh mushy. Also, when the proteins inside the cells lose their watery environment, th
ey unfold and bond to each other, forming a tough, spongy mass.

  To prevent this, the Japanese fishing industry has developed shipboard “superfreezing” techniques for tuna so that fishing boats can remain longer at sea. Fishermen pack the tuna in artificial snow and then immerse them in liquid nitrogen, which rapidly reduces the core temperature of the fish to -70°F. The water molecules don’t have time to migrate and crystallize, so the cellular structures and proteins are protected. The goal is not much different from that of cryonics—the science of deep-freezing human bodies in the hope of future revival. The flesh of superfrozen tuna can taste and feel almost completely fresh for up to two years after harvest.

  At Tsukiji Fish Market in Tokyo, the daily tuna sale begins around 5:00 a.m. in a brightly lit hanger. The concrete floor is hidden by a layer of swirling mist. Visible in the mist are rows upon rows of frosty white pods. They look like a field of alien eggs, fresh from some sci-fi cryonic freezer and ready for hatching. These are flash-frozen, high-quality tuna, solid as rocks. Their fins, gills, and guts have been removed, but otherwise they are intact.

  “There are some tuna that do come in fresh,” Zoran told the students. Some of the best come from New England. “They are in coffins and are ridiculously expensive. How much do you think tuna costs?”

  “Thirteen dollars a pound?” Marcos said.

  “Thirteen dollars a pound?!” Zoran yelled, incredulous. “At Tsukiji in 2001, one 445-pound maguro sold for $173,000!”

  “Wait,” Marcos said, not comprehending. “A hundred and seventy-three dollars?”

  “One hundred seventy-three thousand dollars,” Zoran said. That worked out to nearly $400 per pound. To be sure, that had been an absurdly extravagant bid, for the best of the best—a winter bluefin caught in the waters near Japan, a type of fish that accounts for less than 1 percent of the global tuna catch. Moreover, the purchase had been the buyer’s way of celebrating the first day of business in the new millennium, with an ostentatious show of wealth.

  Even the ridiculously expensive fresh tuna, though, have a drawback—it’s possible for them to be too fresh.

  After an animal dies, its muscles still live. Muscle cells contain a local supply of fuel, in the form of crystals of stored sugar called glycogen. Enzymes in the muscle continue to use and break down this fuel. Eating a fish too soon after death is like eating it while it’s still alive. The muscles are still functional. They are firmly bound together and remain relatively tasteless because the proteins have yet to disassemble into amino acids. Fancy restaurants and sushi shops that serve “fresh kill” sushi from tanks of live fish are not doing their customers any favors. The only sea creatures worth eating straight from the fish tank are eels, squid, and some shellfish—such as giant clam.

  When the glycogen fuel runs out, the muscles finally fail, and the fibers lock into place. The muscles become hard and stiff, and are even worse to eat. This state is called rigor mortis.

  But the enzymes in the muscle keep functioning, and begin to digest the proteins that make up the muscles themselves. The meat softens, and the proteins break down into the smaller compounds that provide flavor, such as glutamate and IMP. Beef doesn’t become soft and flavorful until it’s been sitting around for a couple of weeks after slaughter. Beef producers often age their meat even longer, to allow more IMP to develop.

  Fish generally need between eight and twenty-four hours after death to develop flavor. Fish flesh ages much more rapidly than the flesh of terrestrial animals—and spoils more quickly—because fish are cold-blooded. The enzymes in fish function well at temperatures similar to those in a refrigerator. By contrast, the enzymes of warm-blooded mammals slow down when the flesh cools.

  Bluefin tuna, however, are warm-blooded and very large, so after they’re killed they take longer to age than other fish. Generally, bluefin don’t reach peak flavor until about a week after death. The Japanese have a nickname for bluefin—shibi. It means “four days.” In the age before refrigeration, when someone caught a bluefin, he buried it in the ground for four days before eating it.

  For the sushi chef, bluefin epitomize the fundamental contradiction of serving raw fish. If the meat doesn’t age long enough, it won’t develop sufficient taste. But once rigor mortis is past, the meat rapidly loses firmness and texture. With fish, it is nearly impossible to achieve perfect flavor and perfect texture at the same time. The sushi chef is locked in a delicate dance of timing with armies of enzymes. Instead of cooking, he practices the art of compromise.

  There are other challenges to tuna. If a big tuna puts up a long struggle before death, its core temperature can rise so high immediately after death that its meat can literally cook itself, denaturing the proteins even before rigor mortis sets in.

  The myoglobin in tuna flesh is also highly susceptible to oxidization. When a molecule of myoglobin loses an electron, it turns from bright red to brown. Much of the tuna served at sushi bars in the United States is red only because distributors have gassed it with carbon monoxide, which creates carboxymyoglobin, another bright red molecule. The Japanese government has outlawed this practice, fearing that it could mask spoiled fish.

  However, the greatest challenge regarding the bluefin doesn’t involve killing them but, rather, keeping them alive. Bluefin mature slowly. That means fishermen can easily decimate bluefin populations. Demand for sushi has taken a severe toll on bluefin around the world, though just how badly they are over-fished remains a subject of debate. Environmental groups now recommend that people avoid eating bluefin altogether.

  Bluefin ranching operations capture bluefin from the ocean and fatten them in large pens for high-profit, year-round harvesting. In Australia, tuna ranchers have become some of the country’s richest men. But ranching does nothing to reduce pressure on the wild population—it may even make the situation worse. In contrast, bigeye tuna mature faster and so their populations are more resilient to fishing, as are yellowfin.

  Meanwhile, researchers are learning to breed bluefin in captivity, and are even considering the use of surrogate parents for bluefin to increase production of bluefin eggs. So far, scientists have succeeded in implanting primordial trout cells into female salmon, causing the salmon to produce not salmon eggs, but trout eggs. When fertilized by trout sperm, the trout eggs from the salmon grow into healthy trout. This could be good news for trout populations. Salmon reach sexual maturity more quickly than trout, so as surrogate parents, they can produce trout eggs more quickly than trout can.

  The researchers have suggested that the same sort of arrangement could produce bluefin eggs. Either way, the mass production of factory-farmed bluefin, from egg to fattened adult fish, may yet replace the supply of both wild and ranched tuna—a sad fate indeed for such a majestic, free-swimming fish.

  What type of fish might qualify as a surrogate mother for a giant bluefin?

  Bluefin’s little cousin, the mackerel.

  40

  CARVING THE MOUNTAIN

  “Now,” Zoran said, “how are you going to get a 445-pound tuna into the neta case?”

  Giant tuna are the biggest of the tubular fishes. For the purposes of sushi, filleting a tuna proceeds according to the “five-piece breakdown.” Only the tools are different. At the fish markets, professional cutters first attack the huge fish with industrial table saws and knives the size of swords.

  “No one buys a whole tuna—too much meat,” Zoran said. “You can ask for sections: semi-back meat, midsection meat, belly meat. You can ask for just toro—for seventy or eighty dollars a pound. Or you can ask for a whole side of fish, including toro, in which case the price comes down.”

  For today’s class, Zoran had purchased an entire quarter fillet. He stepped to the refrigerator. He looked over his shoulder at the female student who was pregnant.

  “You know, bluefin is the worst to eat if you’re pregnant. They have the most mercury.”

  In the 1950s, around the quiet bayside town of Minamata in southern Japan, cats
began dancing uncontrollably in the streets. Soon hundreds of people suffered from numb limbs, slurred speech, constricted vision, and uncontrollable movements. Some people’s bodies became locked into contortions; other people tore at their own skin. Women gave birth to a generation of crippled children.

  Eventually the “disease” was traced to fish. The fish were full of mercury. A nearby factory had been dumping its waste in the bay.

  Today, coal-burning power plants emit much of the mercury produced in the United States. Airborne mercury can travel from a factory smokestack halfway around the world. Underwater volcanoes also pump mercury into the sea.

  Like PCBs, mercury spreads upward through the food chain and “bio-accumulates” in high-level predators. Bluefin tuna are the highest-level fish predator of all. Women who are pregnant, or who could become pregnant, shouldn’t eat bluefin, nor should children, and others need to limit their intake. Even canned tuna poses hazards.

  “Do we have bluefin today?” the pregnant woman asked.

  “No, we can’t afford bluefin!” Zoran said. “I got bigeye. I might even get in trouble for that.”

  Zoran pulled out a 3-foot-long package wrapped in white paper. It had been flown in from Hawaii. He peeled away the paper, then a layer of green cellophane.

  “Like Christmas!” he said.

  Inside lay a dark red hunk of muscle. The long piece of meat bulged near the center and was tapered at one end. It was triangular in cross section—13.8 pounds of solid flesh.

  “It smells,” Zoran said. “Can you smell that? I can. The skin’s still on.” He unwrapped it all the way. “Oh, good tuna.” At the bottom, against the skin, it had a nice pale fatty belly.

  “Normally only the head chef cuts tuna,” Zoran said. At Hama Hermosa, not even Zoran was allowed to cut much tuna for the sushi bar. The job belonged to Tetsu, and sometimes fell to the other chefs who had more experience than Zoran. Today provided a rare opportunity for Zoran to work with a full fillet of tuna. He would surrender most of that opportunity to his students.