Sushi is one of my favorite foods. I love the colors, tastes and varieties. I eat it raw, cooked, dipped, sliced, with Wasabi, and even seared with black Sesame seeds! Tuna, whether it's minced and mixed with Srirachia sauce or freshly sliced on its own (as in Tuna Sashimi) is the quintessential ingredient most sought after by Sushi lovers. But how fresh is your Tuna? And, would you be able to tell just by looking at it?
Most people judge a book by its cover, and they judge Tuna just the same. When asked how they judge freshness, people will tell you (in the case of Ahi or Yellowfin Tuna) that a rich red or pink color is most desirable. But having fished for Tuna myself, I have noticed that a Tuna steak will turn brown, or chocolate within about an hour of cutting it. So I researched further into commercial Tuna and found out something interesting.
The Tuna industry has been keeping a little secret from us. That rich, red tuna steak you see in the market may not be what you think it is and it may not even be fresh! It seems that the Ahi Tuna industry have turned to Chemistry to sell their products. Those beautiful, red Tuna steaks that you see at the fish store or at your local Sushi restaurant are artificially colored. The fish has been pumped with carbon monoxide to turn it and keep it red! This is similar to the practice used by the Tomato industry to turn green Tomatoes Red by pumping them with Ethylene gas. The carbon monoxide turns the normally chocolate-colored Tuna a more palatable red. You can do this experiment on your own by putting a chocolate piece of Tuna by your car's tailpipe and watching the difference in color. WARNING: Do not attempt to eat the fish if you have exposed it to your car's exhaust fumes. Your car's exhaust fumes have several other pollutants that you really do not want to eat! This is just an experiment to show you that carbon monoxide will change the color of the fish.
The practice of lacing Tuna with carbon monoxide is not legal in North America according to the FDA and its Canadian counter part. However, as most Ahi Tuna comes from the Pacific, Asian processing facilities ship the fish already treated. There are no laws in Asia which prohibit the use of carbon monoxide to treat fish.
Is it safe? I was not able to find any information on the effects of eating treated Tuna. But It's only common sense to assume that natural is better.
As for freshness, I left a piece of treated tuna outside at room temperature for 24 hours and, although it was obviously spoiled, the color remained the same! A nice deep red, turning a little pink after a while. If this piece was behind glass at the fish market, I certainly would have purchased it. It never turned chocolate. So if you can't tell the quality of Tuna by its appearance, how can you tell? Fortunately, your nose is your best weapon. You should judge Tuna by its smell, texture and taste. It should have a pleasant fishy smell, and firm flesh. And most importantly, it should taste good! And the fact that it's chocolate-colored is just a reaction that any lean protein should have when coming into contact with oxygen and the oxidizing.
There really is nothing wrong with a chocolate colored piece of natural Yellowfin Tuna that is its actual, natural color. The only reason most places won't sell it, is because the consumer has been so used to the carbon monoxide treated tuna that they would not buy the natural stuff. So fish markets are forced to continue importing and selling the treated Tuna. I am not against a nice, red piece of fish, but when something is being sold to me I demand honesty and truth, and this is the reason I wrote this article. I have been enjoying chocolate, organic South Pacific Ahi Tuna for my Japanese dishes as of late, and I will continue to use this product and inform my clients about its origin and character. I simply prefer a more natural food over a processed food. So the next time you are shopping for Tuna, make sure to ignore the color and go for quality instead! It should come down to which piece of tuna smells, tastes and has the best texture.