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Superfrozen Tuna:
Freezing the Clock on Decay

by Anna Mowry
October 2007

The signs on the sushi conveyor belt may boast otherwise, but the ruby-like gleam given off by the tuna nigiri you have your eyes on may not actually smack of freshness. Chances are, it’s gotten a color boost from smoke. Tuna processors add these unappealing additives because conventional freezing can’t sufficiently stave off decay. And since it typically takes two weeks for tuna from foreign waters to reach American shores, there’s ample time for deterioration to attack flavor and appearance. If only it were possible to suspend the natural forces of death that take a toll on tuna, only to later revive the fish to its pristine, fresh-out-of-water state.

Superfrozen otoro
Superfrozen tuna, salmon, hamachi, served as sashimi

It may sound like the stuff of culinary science fiction, but for thirty years the Japanese have been using technology called “superfreezing” to supply their sushi chefs with top-notch tuna. Relying on the science of eutectics (scientific jargon for relationships between freezing points and solids), superfreezing, if properly handled, delivers to your sushi board tuna that’s as fresh as if it leaped directly from the Sea of Japan. Kiyotaka Shinoki of Chanto in New York and Joël Antunes of Joël in Atlanta are among the first chefs in America to use the product in their menus.

Superfrozen Product Preparation and Uses

After an organism dies, its muscles produce chemicals that stiffen flesh and reduce tenderness. The phenomenon is called rigor mortis and it takes place only a few hours after death. Superfreezing tuna to –76ºF delays the onset of rigor mortis, halting its cellular activity and literally freezing decay in its tracks. “When defrosted, the product is truly as it was at the moments before freezing,” says Kenny Ito, Vice President of MC Fresh Inc., a Japanese seafood company that recently opened a superfreezing facility in Secaucus, NJ. “[Our] products go into rigor mortis when defrosted, which is a true sign of a really fresh product.” It’s insurance for that delicate, dissolve on-your-tongue flesh that we crave.

Superfreezing begins at sea, where fishing boats are fitted with specialized freezers that store a catch immediately after gutting and gill removal. Tuna remains in these freezers during transport to kitchens in and beyond Japan. When it’s time to defrost a superfrozen product, rinse it under running water, soak in salted warm water for a few minutes, pat dry and wrap in paper towel, and reserve in the refrigerator until needed. After thawing, the tuna can be prepared just like fish that’s been conventionally frozen. Chef Shinoki uses it in numerous preparations, including carpaccio, grilled steak, and sushi and sashimi.

Chef Kiyotaka Shinoki Preparing Tuna Carpaccio
Finishing Big Eye Tuna Carpaccio with Italian Lettuce Caesar Salad

Conventional freezing methods leave pockets of heat in cells that lead to cell wall breakage; after defrosting, water drains out of broken cells, carrying the flavor with it. Superfreezing locks cell walls in place, so water loss is minimal, and it holds off oxidation, a natural process that results in browning. Since standard freezing can’t prevent oxidation, American producers infuse tuna with carbon monoxide or smoke to restore the rich redness of fresh tuna flesh. These chemicals leave behind unappetizing traces of carbon dioxide and methane. “It’s not allowed in most of the world,” explains Ito. “Chefs may not even know they’re getting old smoked fish.”

Marketing Superfrozen Products

MC Fresh is one of the first companies to market superfrozen fish in this country, offering a product line that includes salmon, hamachi, snow crab, and a variety of tuna species and cuts. Unlike the standard purveyors who pay high shipping costs to ensure that their product reaches kitchens while still fresh, MC Fresh doesn’t need to bear the expenditure because superfrozen items remain in prime condition over a prolonged period of time. The absence of this expense means that MC Fresh product line comes without a steep price hike. But despite this, the company still encounters difficulty when pitching their product line to chefs. “It’s difficult because chefs tend to think we’re just offering more conventionally frozen foods,” says General Manger Ken Kawauchi. “There’s the challenge of explaining its benefits and how it works in a clear and concise way.”

The foie gras industry faces the same challenge. Rougie, a foie gras producer based in Sarlat, France, offers individually quick frozen duck and goose livers that have been flash frozen to –55ºF in one hour, stopping bacterial proliferation and water crystal formation. “Chefs like Joël Robuchon, Alain Ducasse, and Thomas Keller have started using our product, but there is still a huge misperception about this technology in the culinary community,” says Lisa Petrucco of Rougié. “Chefs think all types of freezing are the same. Our products still have expiration dates and need to be stored and handled properly, but we use liquid nitrogen to quickly bring foods down to a very low temperature.”

These purveyors continue to hope that the demand for high-end but highly perishable products will force chefs to recognize the benefits of flash freezing. And with international demand for top-grade tuna increasingly outpacing Japan’s ability to supply, market prices keep rising. “Top-grade tuna will become more and more valuable as it becomes harder to get, so it’s more important than ever to find a way to preserve fish in its prime,” says Ito.

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