I recently read two references to "vintage sardines" canned in specific years and aged in the can for up to 10 years before opening. Supposedly, the sardines improve with age. Do they? What, if any, chemical changes take place over time in canned foods?

Precious few changes take place in properly canned foods, which have been known to retain their wholesomeness and flavor for decades.

For one thing, all food cans today, whether they're steel or aluminum, are lined with plastic coating individually formulated to be nonreactive to the foods they contain. For example, cans used for fish must be particularly resistant to sulfur. So reactions of the foods with their containers are virtually unheard of.

But might there be biochemical changes within the food itself? It's doubtful. All canned food is thoroughly cooked after being sealed, not only to sterilize it but to deactivate enzymes that might otherwise encourage chemical reactions. Again, not a promising setting for change. The generally acknowledged aging of wines in completely nonreactive glass bottles is chemically so subtle that it is still largely a mystery to chemists.

I won't rashly rule out physical, rather than chemical, changes in canned sardines over long periods of time. If packed in olive oil, for example, they could conceivably imbibe more of the oil's flavors and become both tastier and more unctuous as time goes by. But should I ever hear a self-anointed sardinologist declare that the vintage 1989 sardines reach their peak after six years, my skepticism bell would sound a loud "Ding!"

Nevertheless, Patricia Wells, in her "Food Lover's Guide to Paris," tells of Parisians who carefully select sardines by their packing dates and lay them down in their caves (sardine cellars?) like wines, turning the cans every three or four months until the supreme moment arrives for opening and consuming. ("Ah, le bouquet, c'est magnifique!" )

What Is a Sardine, Anyway?

There is no single species named sardine. Sardines are born the moment a label reading "Sardines" is affixed to a can of small fish. They were named after the Italian Mediterranean island of Sardinia, which, like most islands, has a long-standing reputation for being surrounded by fish.

A sardine can be almost any small, fatty fish, but most often is related to the herring. The species primarily caught and canned in Scotland are the sprat or brisling (both Clupea sprattus); in Spain and the Mediterranean, it's the round sardinella (Sardinella aurita); in Norway, it's a sild (any of several species of small herring); and in England and much of the rest of Europe, the young of the pilchard (Sardina pilchardus). Connors Brothers, Ltd. of New Brunswick and Maine, the biggest sardine processor in the world and the only one in North America, cans juvenile Clupea harengus, otherwise known as Atlantic herring.

Now, to reverse a hackneyed simile, how do they pack the sardines into those cans like New Yorkers in the subway during rush hour? Surprisingly, it is still done mostly by hand. Machines sort the fish by size and decapitate, eviscerate and de-tail them, but human hands and eyes still do the best packing job.

What about the bones, guts and skins we find in many canned sardines? Are they edible? Yes. In the so-called Mediterranean method of processing, the fish are eviscerated and thoroughly cooked, either by steaming or frying, which is more expensive. In the Norwegian method, the fish are not eviscerated; they are kept alive in nets for at least 48 hours, during which time they complete the digestion of their food and clean themselves out. Then they are hot-smoked. The bones and skins are good for you; the bones contain calcium and the skins contain omega-3 fatty acids.

Unincarcerated Sardines

I received this week's question about sardines from a reader in Vienna, just as I was returning from Spain's Costa Brava -- specifically, Catalonia and its capital city, Barcelona. Catalonia is a self-governing region in northeastern Spain with its own language and culture. It is the birthplace of surrealism, not only in art (Joan Miro and Salvador Dali were Catalan) and in architecture (Antonio Gaudi, ditto), but more recently in gastronomy, with the worldwide recognition of Catalonia's most creative and surrealistic chef, Ferran Adria.

While in Catalonia, I ate some of the world's best sardines, not to mention anchovies and several anonymous little fishies.

We Americans may think of sardines as the contents of those small, flat cans with the rounded corners -- you know, the ones that splatter oil or sauce all over the counter when we tear off the lid. But in Catalonia the sardine rises to gastronomical eminence. There, fresh sardines six to eight inches long are either deep-fried or grilled (a la planxa in Catalan), often over a driftwood fire at the beach, and sprinkled with coarse salt. That's all. Tinsmiths need not apply.

What Is an Anchovy?

Exactly what are those flat, brown and unconscionably salty ribbons of fish flesh in the cans and jars? Do they come from a single species or many?

There are about 125 species of anchovy, but only one dominates the culinary scene: the Mediterranean Engraulis encrasicolus. Called anchoas or boquerones ("big mouths") in Spain because they have long, gaping jaws, the silvery fish in their natural state appear not to be even distantly related to the canned mystery strips we use in Caesar salads and on pizzas.

In eastern and southern Spain, whole, fresh anchovies are crisply fried and eaten bones and all. Or they are salted and packed in barrels to cure for four or five months. They are then rinsed, gutted, beheaded, and their spines pulled out, leaving two fillet strips attached to the tail. No cans, no oil, no wanton saltiness. The mild, soft, white boquerones en vinaigrette are delicious on a round of grilled bread in a tapas bar, accompanied by a glass of cava, the Catalan sparkling wine.

If you're ever lucky enough to find fresh sardines or anchovies in an American fish market, grab them and grill them. You'll think you're on a beach in Spain.

Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author, most recently, of "What Einstein Told His Cook: Kitchen Science Explained" (W. W. Norton, hardcover, $25.95). He can be reached at wolke@pitt.edu.