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Stepping inside IMP Foods in San Mateo is like wading into the ocean - all salty-scented and shivery cold. As well it should be.

Sea creatures from all over the world are brought to this wholesaler before ending up on plates at Bay Area sushi bars and upscale restaurants around the country.

IMP Foods is one of only a handful of businesses in the Bay Area that specialize in sushi-grade or sashimi-grade seafood. Thats seafood thats so fresh and is handled so carefully it can be safely eaten raw.

It wasnt so long ago that raw fish was hardly ever served outside a Japanese restaurant. Now, more and more white-tablecloth establishments tout seared ahi or tuna tartare - made with sushi-grade fish.

Consumers should know that sushi is a delicious but highly perishable form of cuisine, says Glenn Sakata, IMP Foods general manager. To handle it properly requires manpower, expensive equipment, an efficient delivery system, discipline, knowledge, experience, dedication and beyond.

When IMP was established in South San Francisco 18 years ago, the company had only two employees and 10 customers. Now, the privately held company, a sister company to Japanese-owned seafood wholesaler International Marine Products in Los Angeles, has grown to 35 employees and 300 customers. Both are owned by Japan-based Eiwa Group, a conglomerate that includes restaurants, a cooking school, a seafood export business and a marshmallow factory, all in Japan.

IMP Foods, which does $20 million in sales annually, is best known for its vast array of seafood products from Japan. Its seafood, which comes from more than 30 countries, is served at about 75 percent of the Bay Areas sushi bars, Sakata estimates, including Ebisu in San Francisco, Kirala in Berkeley, Chaya in San Francisco, Seto Tempura in Sunnyvale and Akane in Los Altos. It is also featured in such upscale restaurants as Masas in San Francisco, Spago in Palo Alto, Farallon in San Francisco and Charlie Trotters in Chicago.

Although the public cant buy directly from IMP, you can purchase its seafood at markets such as Mitsuwa in San Jose, Nijiya in Mountain View, Suruki in San Mateo and Tokyo Fish in Berkeley.

Jody Denton, executive chef of San Franciscos hip French-Asian restaurant Azie, has been buying ahi, albacore, hamachi, flounder and Spanish mackerel from IMP for a year to serve as sashimi or in parfaits layered with avocado, cucumber and rice.

With local fish purveyors in San Francisco, the quality is good by general American standards, Denton says. But the standards for raw fish for the Japanese are like 12 steps above. IMP really cares for the fish, and the quality from them on any given day is far superior. For a raw preparation, where fish is the whole point of the dish, we go with them. Exacting assessments

Many companies say all sushi-grade fish is the same quality, but Sakata disagrees. When a fish arrives at IMP, a thermometer is used to check its temperature. For most fish, the temperature should register 37 degrees, just above freezing and below the level that promotes the growth of toxins and pathogens, Sakata says. The tail meat is cut to check color, and a long probe is stuck into the body to extract a cross-section to determine texture and fat content.

Besides how the fish is handled and the temperature its stored at, other variables that affect grading include where it was caught - every species has a natural habitat - and the season in which it was caught. The best time to eat salmon, for instance, is March through May, just before they would swim upstream to spawn, because they have more fat then, Sakata says.

Thats because more fat means more flavor. And the same species may have more fat at different stages of life. For instance, Sakata says, a 2-year-old yellowtail (hamachi) is fatty and fairly firm. But that same fish at age 4 has a much whiter, softer, fattier and more buttery taste and texture. In fact, it has so much fat that soy sauce will barely stick to a piece of it done sashimi-style, much like water beads off a well-waxed car.

At IMP, seafood is ranked either sushi-grade No. 1 (excellent) or sushi-grade No. 2 (good), Sakata says. Anything thats No. 2, we reject, he says. Its sent back to the supplier.

With its network of hundreds of fishermen and seafood brokers around the world, it takes IMP only from 36 hours to three days to get the fish from the ocean to a restaurant table, depending upon whether the seafood originated in this country or overseas.

For that level of freshness, work starts early. By 4 a.m., workers in rubber boots, rubber gloves and hair nets are scurrying about the refrigerated warehouse, unloading shipments from San Francisco International Airport. For the next five hours, theyll fill each restaurants order, loading up wax-coated, waterproof boxes with seafood on ice to be delivered by 11 a.m.

A few particularly finicky chefs, such as Sam Sugiyama, owner of Sushi Sams in San Mateo, prefer to pick up their own fish every day so they can personally inspect everything.

This is the best place, says Sugiyama, as he sniffed and poked a boiled octopus from Japan. They have the freshest stuff.

Inside the warehouse, its practically an aquatic exhibit. There are bins of Pacific oysters from Seattle; their superior quality makes them the only oysters IMP Foods will sell, and only from September through May, which the wholesaler considers the best season. Nearby are oblong razor clams from Boston, herring roe from Canada, whole Thai snapper from New Zealand, monkfish and its foie-gras-like liver from Rhode island, sardines from Monterey Bay, and geoducks from western Canada that look like an anteaters schnoz poking out of a giant clamshell as big as your hand.

More than fish

IMP also sells other sushi accouterments: shiso leaves from Oxnard, bamboo leaves from Japan, fresh wasabi root from Japan, and a new powdered wasabi from Canada thats the terra cotta color of clay and spicier than the usual green variety.

But the biggest seller by far is tuna. And its the most expensive. Bluefin, with its elegant taste and meat as red as beef, contains one and a half times the fat of the milder-tasting yellowfin - and it sells for three times the price. A room is set aside for filleting bluefin and other large tuna, which can tip the scale at 700 pounds. Prices vary for different cuts. The fattiest section of the bluefin belly, prized for its rich texture and flavor, is $35 a pound wholesale.

Sushi chef Craig Kuwabara of Palo Altos Highashi West restaurant will be the first to say, though, that the quality is worth the price. He buys almost all his fish from IMP - all for the sushi bar, never the stove.

We dont want to waste it, he says. With fish this good, a little soy sauce and wasabi is really all you need.

Sushi grade is subjective rating
Does sushi grade always guarantee that fish is the freshest and best it can be?

Not necessarily.

Diners and consumers should be aware that there are no state or federal regulations regarding what can be called sushi grade. That determination is made by individual seafood dealers based on subjective assessments of factors such as texture, fat content and color. As a result, fish that one dealer may label as sushi grade another might dismiss as sub-par.

With sushi-grade, you are dealing with both sensory and safety issues, says Michael Hernandez, chief of the seafood safety program for the food and drug branch of the California Department of Health Services. Its the smell, the color, the taste, as well as safety considerations with parasites and toxins.

With regard to food safety, California seafood processors and dealers are required to assess their product and develop plans to ensure the fish is safe to eat raw, using guidelines from the U.S. Food and Drug Administration. But because those plans are tailored to each dealer and are different for various types of fish, safety plans can vary widely.

For instance, FDA guidelines recommend that all fish to be eaten raw, other than tuna, first be frozen to kill parasites. But California regulations require freezing only if parasites are found. (Tuna is exempt because its not prone to parasites.)

In the United States, human parasitic infections from seafood are rare, according to the National Academy of Sciences. In California, incidents of illness from parasites, toxins or bacteria from raw fish also are uncommon, Hernandez says. Still, because few foods have zero risk, he adds, consumers who plan to eat raw seafood should patronize reputable seafood stores and restaurants that turn over seafood stock frequently.

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