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October 26, 2004

BehindTheMedspeak: What does carbon monoxide do to you - if you eat it?


Julia Moskin, in a story that appeared on the front page of the October 6 New York Times Dining Out section, brought us unpleasant news.

It seems that sushi bar tuna is being routinely gassed with carbon monoxide to keep it looking bright red for as long as it's displayed.

It appears there is no end to this sort of stuff.

Here's the story.

Tuna's Red Glare? It Could Be Carbon Monoxide

Buyers of fresh tuna, whether at the sushi bar or the supermarket, often look for cherry-red flesh to tell them that the fish is top quality.

But it has become increasingly likely that the fish is bright red because it has been sprayed with carbon monoxide.

The global seafood trade has expanded so much over the last decade that tuna, once a seasonal delicacy, is available year-round.

But getting it to consumers while it still looks fresh is difficult.

Tuna quickly turns an unappetizing brown (or "chocolate,'' as it is called in the industry), whether it is fresh or conventionally frozen and thawed.

Carbon monoxide, a gas that is also a component of wood smoke, prevents the flesh from discoloring.

It can even turn chocolate tuna red, according to some who have seen the process.

People in the seafood industry estimate that 25 million pounds of treated tuna, about 30% of total tuna imports, were brought into the United States last year, mostly from processors in Southeast Asia.

Retailers in the United States buy it already treated.

The Food and Drug Administration says the process is harmless.

But Japan, Canada and the European Union have banned the practice because of fears that it could be used to mask spoiled fish.

Carbon monoxide preserves only the color of the fish, not its quality.

Suppliers and retailers who use the treated fish say the process allows them to sell high-quality, flash-frozen fish that still looks good enough to eat.

Jerry Bocchino, an owner of Pescatore, a fish store in Grand Central Market in New York, said that his sales of tuna have tripled since he switched to the treated kind two months ago.

"With fresh tuna, you're always racing the clock to keep the color and keep it from spoiling,'' Bocchino said.

"And once it turns brown, no one wants to buy it. People love the color of this stuff."

Tim Lauer, a seafood dealer in the Minneapolis-St. Paul area, said that most sushi bars and supermarkets there have switched to the product since it was introduced in the late 1990s.

"I've lost all my sushi customers for tuna, since I won't sell it," he said.

Just because a slice of tuna is brown, it does not mean it is not fresh.

And other factors determine the color, including the fat content, species, and cut.

The finest fresh bluefin tuna, which sells for up to $40 a pound at Tokyo's wholesale fish markets, is not a deep red but a pale pink because of the fine web of white fat that permeates the red flesh.

Top-quality toro is often a brownish-red.

But for most consumers around the world, vendors say, lollipop-red flesh signifies freshness and quality.

Tuna treated with carbon monoxide is bright red when first defrosted, sand fades within a couple of days to a watermelon pink.

But "you could put it in the trunk of your car for a year, and it wouldn't turn brown," said one sales representative at Anova Foods, a distributor in Atlanta, who spoke on condition of anonymity.

The use of carbon monoxide in food is hardly new, as any barbecue or smoked salmon fan should know.

Wood smoke contains carbon monoxide.

But the gas used by many overseas producers, although tasteless, is more concentrated; it can be as much as 100% carbon monoxide, said Bill Kowalski, an owner of Hawaii International Seafood.

American processors like Hawaii International and Anova Foods are racing to market their own versions of the technology, using wood smoke that is filtered to remove the elements that make food taste smoky.

These processors use lower concentrations of the gas and tag their product with trademarked names like Tasteless Smoke, Clearsmoke and Crystal Fresh.

Opinion about carbon-monoxide-treated tuna is sharply divided, and illustrates the complex issues that consumers have to wade through at the fish market.

To supporters like Bochino, Kowalski, and Dr. Steve Otwell, a researcher at the University of Florida, carbon monoxide treatment is an important advance in food safety that accomodates the realities of the marketplace.

Instead of fresh tuna that is likely to spoil quickly, they reason, consumers can get a high-quality frozen product that can be transported safely, thawed when needed, and keep its fresh look.

"The industry scrambles to get fresh tuna to market, but the reality is that by the time a long-line Pacific tuna makes it to an American supermarket, it could be as much as 30 days out of the water," Dr. Otwell said.

"That's much more of a health risk than treated tuna, as long as the raw material is good and the treatment is controlled."

Roman Choudhury, the manager of two sushi restaurants in Manhattan, buys treated tuna when he cannot get it fresh, particularly for tuna rolls.

"At my price point, it's almost impossible to have a steady supply of fresh tuna," he said.

"And people always, always want tekka maki."

Detractors call the process risky and dishonest.

"There's no reason to do this other than to deceive the consumer," Lauer said.

"There are natural solutions to the problem of browning."

One is ultra-low-temperature freezing, which keeps tuna at about –80° for months or even years without browning.

But maintaining such low temperatures during the long trip from boat to plate is a very expensive proposition.

Caroline Smith DeWaal, food safety director for the Center for Science in the Public Interest, a nutrition advocacy group, said, "Anything that masks the true age of a piece of fish is a public safety risk."

As tuna ages, it becomes more likely to cause scombrotoxin poisoning, which is rarely severe or fatal.

It is the most common form of food poisoning from seafood in the United States, the Center said.

The F.D.A. has put carbon-monoxide-treated tuna on its list of substances generally regarded as safe.

The agency permits its use to preserve the color of fresh tuna, not to enhance brown tuna, and requires stores to label treated fish.

But they often do not.

What does all this mean at the market?

Any tuna that is hot pink has probably been treated with carbon monoxide.

Tuna that is bright red may be extremely fresh, and therefore very expensive, or may have been treated with the gas.

"Outside of Hawaii bright red tuna that is selling for less than $12 a pound is probably treated," said Lauer.

"On the other hand, there's nothing to stop people from selling treated tuna for $20 a pound if they can get away with it."

Well, that's depressing.

Maybe someone needs to invent a device, sort of like a meat thermometer, you stick into a piece of fish to get a carbon monoxide level.

I wouldn't be surprised if someone at one of the fish processing companies isn't, as you read this, putting the final touches on some fish-coloring version of Liquid Smoke.

That way, you could soak the fish in it or simply sprinkle it on old, funky tuna to perk it up and make it more appealing and marketable.


I guess the only solution, really, is to make one's way to Tokyo's Tsukiji Fish Market - the world's greatest - and enjoy the planet's freshest tuna at one of the many surrounding sushi bars.

October 26, 2004 at 10:01 AM | Permalink


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Tracked on May 20, 2006 10:38:36 PM


It's risky and ridiculous that we should be subjected to chemicals in our food and not even know it. That is the trend these days. Not good..so speak up..voice your objections you fish lovers. Years from now the truth will be known but it will be too late. I've stopped buying or eating raw fish unless it's fresh off my neighbor's boat.

Posted by: Leialoha Dilliner | Mar 1, 2008 8:48:47 PM

Can carbon monoxide be detected or measured in fish in the laboratory

Posted by: M Murphy | Jan 18, 2005 2:58:16 PM

I am a journalist in Australia looking to find someone in Australia who can comment against Carbon Monoxide treated tuna? Can you help?

Can it be tested for?

Posted by: James Thomas | Dec 6, 2004 8:53:24 PM

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