Aging canned goods: Why time and heat can make your canned tuna and Spam even more delicious.

Amazing Flavors Can Develop When You Keep Canned Goods Past Their Best-By Date

Amazing Flavors Can Develop When You Keep Canned Goods Past Their Best-By Date

What to eat. What not to eat.
March 4 2013 5:20 AM

Age Your Canned Goods

Why I now think of best-by dates as maybe-getting-interesting-by dates.

Cans of sardine
Canned tuna, sardines, chicken spread, and Spam all have their own appeal

Photo by Jimin Lai/AFP/Getty Images

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The following article originally appeared in the Apocalypse Issue of Lucky Peach, a quarterly journal of food and writing. It is available online only in Slate. Subscribe to Lucky Peach here.

As a resident of earthquake country, I’ve long maintained a sizable stash of emergency canned goods. I buy tuna and beans and chili by the case at big-box stores and store them in trash cans in my backyard. I used to keep track of their best-by dates and replace them regularly. And then a few years ago I heard about vintage canned sardines, and I tasted prized, pricey Galician conservas. (Leave it to the French and Spanish to recognize the gastronomic potential of sterilization!) Now I think of best-by dates as maybe-getting-interesting-by dates. And to my trash can of aging staples I’ve added some hand-packed delicacies, to make sure that survival includes at least a few little pleasures.

It was a French chef and confectioner who started preserving foods with heat and airtight containers, so of course he cared as much about the quality of the result as he did about its longevity. At the beginning of the 19th century—decades before anything was known about microbes—Nicolas Appert thought the key to preservation was protecting foods from the air, and based his heating times mainly on what he considered culinarily appropriate for particular foods. He called for partly cooking foods in ordinary pots and pans, then transferring them to glass jars, corking the brim-filled jars, and finishing the cooking in a boiling water bath. Broths and gravies could be cooked for an extra hour without suffering, Appert wrote, “but there are articles which will sustain a great injury from a quarter of an hour’s or even a minute’s too much boiling. Thus the result will always depend upon the dexterity, intelligence, and judgment of the operator.”

English and French inventors, and Appert himself, soon improved on his original method by replacing the fragile glass and corks with more durable metal cans, and the water bath with pressure cookers. Appertization wasn’t foolproof—foods sometimes spoiled and cans exploded—but it worked well enough that European navies of the day quickly adopted canned supplies. Some cans lasted more than a century. In 1938, an English chemist reported on his analysis of several cans from a Royal Navy expedition to the Arctic in 1824; they had been brought back unopened and kept in a museum. The scientists didn’t actually sample and describe the beef and tripe and carrots themselves, but they did report that the foods looked and smelled right and that lab rats ate them with gusto and no ill effects.

But it wasn’t until after 1895 that canned food became the reliable product it is now. A scion of the Underwood family—canning pioneers in the United States—consulted an MIT chemist named Samuel C. Prescott—later the founding president of the Institute of Food Technologists—about exploding cans of clams. Their experiments revealed the presence of heat-resistant bacteria whose inactivation required raising the can center to a minimum of 250 degrees Farenheit and holding it there for at least 10 minutes. That finding set the standard modern protocol for canning low-acid foods.

This punishing heat treatment helps create the distinctive flavors of canned goods. So does the hermetically sealed container, which means that after any preliminary cooking outside the can—tuna is steamed to remove moisture, for example, and the best French sardines are lightly fried—oxygen can play only a limited role in flavor development, and that whatever happens in the can stays in the can—no aromas can escape. Hence the common presence of a sulfurous quality, which may be eggy or meaty or oniony or cabbagy or skunky, from compounds like hydrogen sulfide, various methyl sulfides, and methanethiol. Some of these notes can gradually fade during storage as the volatiles slowly react with other components of the food.


The overall flavor is nothing like freshly cooked foods. Food technologists often refer to it as “retort off-flavor.” But it’s only off in comparison to the results of ordinary cooking. It’s really just another kind of cooked flavor, an extremely cooked flavor, and it can be very good. Canned tuna, sardines, chicken spread, and Spam all have their own appeal.

A few intriguing foods are sealed in cans without extreme cooking. The most infamous is Swedish surströmming, barrel-fermented herring that continues to ferment in the can, which swells with profoundly offensive gases and becomes hazardous to transport. Easier going and easier to find in North America is Cougar Gold cheese, which has been canned since the 1940s in the creamery at Washington State University in Pullman. It’s not like Velveeta or other processed cheese products—cooked slurries of various anonymous cheeses and emulsifying salts. The WSU dairy students make a regular cheddar curd and then seal it right away in cans, which are kept and sold refrigerated. The various lactic acid bacteria don’t need oxygen to survive, and their enzymes slowly develop the cheese’s flavor. Fans of Cougar Gold age their cans for years, sometimes decades. But because everything stays in the can, moisture included, the flavor and texture are unlike a true cheddar’s. My first bite reminded me of the aroma of canned chicken spread. Incongruous, but it grew on me.

Standard canned goods aren’t generally deemed age-worthy. Food technologists define shelf life not by how long it takes for food to become inedible, but how long it takes for a trained sensory panel to detect a “just noticeable difference” between newly manufactured and stored cans. There’s no consideration of whether the difference might be pleasant in its own way or even an improvement—it’s a defect by definition.