Marlene Parrish - What Einstein Told His Cook 2

Tuna cosmetologists can of course buy their carbon monoxide gas in steel tanks, like many other gases. But there’s a cheaper way to get it: by burning wood. Because of the incomplete combustion process described above, wood smoke contains carbon monoxide. The tiny particles that make smoke smoky can be filtered out along with the tarry chemicals that give smoke its flavor, leaving a mixture of gases—carbon dioxide, carbon monoxide, nitrogen, oxygen, and methane—called filtered smoke or tasteless smoke. It can be used instead of pure carbon monoxide to brighten the fish’s color. The justification is made that tasteless smoke can be no more harmful than “whole smoke,” traditionally used to make smoked fish and other meats. According to the FDA, however, foods treated with filtered smoke may not be labeled “smoked,” because the expected smoked flavor isn’t there.

The irony in all this is that the color of untreated tuna is not an indicator of its wholesomeness. Myoglobin’s color changes take place long before the fish has begun to deteriorate. The association of bright color with freshness is all in the consumer’s mind.

So is there anything wrong with carbon-monoxide-treated tuna? Not because of any presumed health hazard. But there will always be a few rascals who try to conceal over-the-hill fish by touching up its color, and that is an actionable offense according to the FDA. Moreover, research by the Food Science and Human Nutrition Department of the University of Florida has shown that dangerous time-induced spoilage can continue in monoxide-treated fish even though the color remains bright, perhaps luring unsuspecting diners to disaster like a gussied-up siren.

Because of the possibility of abuse by tuna suppliers, several countries prohibit carbon-monoxide-treated fish. Sushi-conscious Japan has outlawed it since 1997, while the European Union has begun to enforce its ban only since early 2004.

Your best resource as a consumer is, as usual, your confidence in your source. You shouldn’t eat raw fish in any but the most trustworthy sushi establishments anyway, for reasons unrelated to carbon monoxide. If a given restaurant would never sell contaminated or spoiled fish under other circumstances, it would certainly never sell contaminated or spoiled fish that has been cosmetically enhanced. Fresh tuna has a clean flavor, relatively firm texture, and of course, no odor, no matter what its color. So if in doubt, just shut your eyes and let your mouth and nose be your guides.

And remember that yellowfin tuna varies in color from pink in smaller fish to deeper red in larger fish, so once again the color itself is no indication of freshness.

If your fish is a bright, unnatural-looking watermelon red, it has probably been treated with carbon monoxide or filtered smoke. But there is no known health hazard if the fish itself is fresh and clean.

CHEAPSKATE NO MORE

All my life, I’ve heard rumors that some scallops sold in fish markets aren’t scallops at all, but have been punched out of skate wings or other kinds of fish. Any truth to that?

Ican’t say that it’s never been done, but I doubt that it has been done very often. And surely few of us would continue to patronize a fishmonger or restaurateur who had been found to try such a trick. At one time, skate was a low-priced fish caught accidentally (in the “by-catch”) by fishermen in pursuit of more lucrative quarry. But no more. Skate isn’t as cheap as it used to be, and the crime wouldn’t pay as well as it used to.

An even better reason to doubt this urban legend is the fact that running through the middle of a skate wing is a thin sheet of plastic-like cartilage. A “scallop” with a layer of plastic in the middle wouldn’t be very convincing. It’s true that if the skate is big enough (the common skate can run up to 200 pounds), it can be filleted into two slabs, one above and one below the sheet of cartilage, and convincingly thick “scallops” could be punched out of each. But there are easier ways to make a dishonest buck.

(If you ever decide to go into scallop counterfeiting, beware of the tiny, almost microscopic barbs on the skate’s skin. They don’t sting, but they prickle annoyingly. And don’t ask me how I know.)

Known as raie in France, the skate is indeed a kind of ray, a term that covers several families of flat, bottom-dwelling fish that, like sharks, have cartilage instead of bones. Rays (family Rajidae) range from the most-often-eaten European skate ( Raja batis ) to stingrays with poisonous tails and giant manta rays that can weigh up to 3,000 pounds. Rays’ bodies are flattened out into ribbed, fanlike “wings” that undulate gracefully for locomotion. They are all edible, but some are not exactly gourmet fare.

Even if cookie-cutter cylinders of skate wing were to be passed off as scallops, they wouldn’t fool anyone who has ever eaten skate, sometimes sold as raja fish. The flavors and meat colors are similar, but the texture is all wrong. The skate’s toothsome, long-stranded texture is more like that of crabmeat than scallop. Be suspicious of any scallop that seems to come apart in strands or layers.

And by the way, those little hollow, rectangular, leathery black “mermaid’s purses” that you see washed up on beaches or tangled in seaweed are the egg cases of skates, originally containing two large eggs and abandoned after the young ’uns have hatched.

THE FOODIE’S FICTIONARY:Crab Louie—the husband of Nag Maggie

Sidebar Science: Iced skates

WITH SOmuch wing surface area exposed to the sea, rays would be at risk of having water extracted from their tissues into the saltier seawater by osmosis. As a defense against this potential dehydration, the rays’ body fluids contain a large concentration of a highly soluble, nitrogen-containing chemical called urea, CO(NH 2) 2. (Yes, it was first discovered in urine, but it is made synthetically.) Urea breaks down into carbon dioxide and ammonia, so rays, even the freshest ones, tend to smell of ammonia, normally an indication of spoilage in other fish. The ammonia smell can be expunged by soaking the fish in any acid, such as lemon juice or vinegar, or by keeping it refrigerated—or better yet, on ice—until all the urea is gone.

EGGS, DRY-CLEANED AND PRESSED

My aunt came back from Sicily and brought me some bottarga. I know it’s bottarga because it says so in big letters on the package, but the rest is in Italian. (I didn’t want to sound ungrateful by asking, “What am I supposed to do with this?”) I know it’s some kind of fish eggs, but it’s almost as hard as a rock. What is it, and what can I do with it?

Icould tell you it’s rockfish roe, but I won’t.

Bottarga is dried, salted roe from either the Mediterranean tuna ( tonno in Italian) or the gray mullet ( mugine ). Bottarga di tonno (also known as uovo di tonno, or tuna eggs) and bottarga di mugine are local specialties of Sicily and Sardinia, Italy’s two large Mediterranean islands, and are valued as delicacies in the rest of Italy.

The roe sac is removed as soon as the female fish is caught. It is then washed; salted; pressed, traditionally between wooden planks or marble slabs; and dried, traditionally in the sun, for one or two months. It comes out looking like dark amber wooden boards, firm enough to be grated like Parmesan cheese. The salt helps the drying process by extracting water from the crushed eggs, which glue themselves together because of their albumen and fat.

Tuna bottarga has a bright, sharp salty flavor, whereas the mullet version is somewhat milder. The best thing to do with either is the simplest: make Sardinia’s spaghetti alla bottarga . To a plate of cooked spaghetti, add extra-virgin olive oil, chopped garlic, parsley, and red pepper flakes. Toss, and grate some bottarga over the top before serving. Remember that bottarga is a condiment, quite salty and fishy, and a little goes a long way.