What do the dates on canned goods mean?
The dates on canned goods don't reflect when the food will become unsafe to eat, they are based on quality control concerns. Manufacturers don't want customers to eat a can of food that has been sitting around so long it has become less appetizing, because the customer will be less likely to buy their product in the future. The date on the can is the manufacturer's way of saying "it might not taste good after this date, so if you eat it and it isn't as good as you hoped, don't blame us".
Here's the short answer: Those "sell by" dates are there to protect the reputation of the food. They have very little to do with food safety. If you're worried whether food is still OK to eat, just smell it.
One of the places that knows most about the shelf life of food is a scientific establishment in Livermore, Calif., called the National Food Lab. At the NFL, they put food on shelves for days, or weeks, or even years, to see how it holds up.
Sometimes, they'll try to accelerate the process with 90-degree heat and high humidity.
And then, from time to time, they'll take some of the food — whether it's bagged salad greens, breakfast cereal, or fruit juice — off the shelf and place it in front of a highly trained panel of experts who check the taste and smell and texture.
"You would think that everybody can taste and smell food, but some of us are much better at it than others," says Jena Roberts, vice president for business development at the NFL. The lab has 40 of these food tasters on staff. "They are the most fit people in the group," says Roberts. "Because they don't eat the food. They expectorate it. Which is a fancy college word for spit it in a cup."
The experts give the food grades, in numbers. The numbers go down as the food gets older. Bread gets stale. Salad dressings can start to taste rancid.
John Ruff, president of the Institute of Food Technologists in Chicago, says the companies that sell this food take a look at those grades and decide where they will draw the line, to protect the reputation of their products.
"If the product was designed, let's say, to be a 7 when it was fresh, you may choose that at 6.2, it's gotten to the point where [you] don't want it to be on the market anymore," he says.
"If it's 6.0, would most people still find it reasonably good? Absolutely," he says. "But companies want people to taste their products as best they can at the optimum, because that's how they maintain their business and their market shares."
This is all organized and carried out by food companies; there's no federal law that requires dates on any food except for infant formula, although some states do require sell-by dates on milk or meat.
Still, these dates don't really tell you anything about whether food is safe.
- NPR, The Salt: Don't Fear That Expired Food
Basically, the manufacturers want their product to be consistent, so they store some cans of their stuff for long periods of time and then have testers sample the food from these old cans. The testers look for several things:
Texture (e.g., do the vegetables still have some firmness to them, or are they mushy and gross?)
Appearance (e.g., are the colors still bright and vibrant? Is the liquid separating into layers? Is everything turning grey and stale-looking?)
Flavor (e.g., does it still taste fresh, or has it become bland?)
When a can of a certain age is judged to be unappealing on any or all of these criteria by a certain percentage of testers, the manufacturer says "Okay, this is too old!" Then they test slightly newer cans, and keep going until a certain percentage of testers say the food hasn't changed much in terms of how palatable it was when it was fresh.
How do you know if the food inside a can is still safe?
In theory, canned goods will be safe to eat indefinitely as long as a few things don't happen:
Bloating cans and collapsing cans: This is indicative of contamination. Bacteria are eating the stuff in the can and producing gas as they digest it. This is VERY bad. It is also bad if the can has begun to pucker or collapse in on itself, for more or less the same reason - organic activity is taking place inside the can and changing the pressure inside of it, indicating contamination by bacteria.
Compromised cans: If the stuff in the can is exposed to the environment by a leak or hole in the can, bad stuff gets in, and the food spoils. Holes, leaks, oozing, weak seals along the edges, rusted seals, dried crap on the outside of the can - these are all things to avoid.
Rusted cans: The rust alone is dangerous if consumed, and is also indicative of the can being compromised.
Cans that LOOK okay, but smell like death when you open them: Obviously, you can't/won't see every problem, so occasionally, a can will pass the visual inspection but fail the olfactory inspection. This usually means the can was indeed compromised, but for whatever reason, the flaws in the can weren't visible. Somehow, bad stuff got in and spoiled the food. It is basic common sense that if you open a can and the stench it emits makes you nauseated, you shouldn't eat it.
So the basic idea is that if the can is still sealed, airtight, not bloated or concave, and not rusty, the food inside is almost certainly safe to eat.
How long will canned food in an intact, uncompromised can remain safe to eat?
We don't know, because some of the first canned food ever produced is still edible.
A US Army officer brought a can of cake home from Vietnam, stored it in his house for 40 years, then ate it on camera:
A British couple received a canned chicken as a wedding gift. The husband said he'd eat it on their 50th anniversary, and he meant it. They ate the chicken 50 years later, and they were fine.
An elderly German man had been saving a can of lard purchased in 1948 for an emergency. After 64 emergency-free years, he gave up and used it to cook his food.
In the US, researchers have tested food canned over a century earlier:
Canned food, in particular, can stay safe for a really long time. In 1974, scientists at the National Food Processors Association in Washington, D.C., got their hands on several old cans of food.
Janet Dudek, now semi-retired and living in Vienna, Va., was among the scientists who analyzed this old food. Her assignment was a can of corn, vintage 1934, that was found in someone's basement in California.
When they opened the can, Dudek says, the contents looked and smelled pretty much like ordinary canned corn. Analysis showed that it had most of the usual complement of nutrients — although there were lower levels of a few, such as vitamin C.
Results were similar for century-old canned oysters, tomatoes and red peppers in cans recovered from a sunken steamboat, buried in river silt near Omaha, Neb.
Dudek says, as far as she knows, nobody actually tasted this food. That just wasn't done, she says. But they probably could have. "It would have been safe to eat if the can itself maintained its integrity," she says.
American talk show host Jay Leno once ate part of a fruitcake that had been canned 125 years earlier.
A few years ago, some historians in Russia uncovered a stockpile of canned food. It turned out they were left over from the supplies carried into Russia by Napoleon's army. In fact, modern canning was invented by the French to supply Napoleon's troops with a reliable source of food when they were conquering most of Europe.
The cans uncovered by these historians contained smoked oysters, and the oysters were still safe to eat. How do we know they were safe? Because the historians opened a couple of cans and ATE THE OYSTERS. The cans kept their contents safe for about 200 years.
Incredibly, this isn't the oldest preserved food eaten by modern people. Archaeologists in Egypt frequently find sealed pots of honey in excavated tombs, and on several occasions, they have opened the jars and tasted the honey, and haven't suffered any harmful effects from it. Thus, some foods - even though they weren't sealed by modern methods - can remain safe to eat for several thousand years.
Believe it or not, 5,000 year old honey doesn't hold the record for safe-to-eat preserved foods, either. You might think that the "oldest food ever eaten" distinction would go to paleontologists who ate a 36,000 year old bison carcass - but you'd be wrong, because scientists once ate a 250,000 year old mammoth carcass.
Other types of preserved food:
Obviously, most of the freezers and fridges stopped working when the power cut off, so you don't want to eat any unpreserved, perishable food you find. Same goes for produce sold fresh. But you could certainly eat any dried beans, rice, pasta, etc, you happen to find.
Spices will be musty and bland, but edible. Flour may go stale, but you can still eat it if you find it (and if it isn't contaminated by water, vermin, etc). Yeast may or may not work after a few months. Canned and bottled drinks will taste funny after a while, but if you make sure the container isn't compromised, it should be safe. Honey lasts forever, as far as we can tell. So does salt. Sugar is likely to attract bugs, and after a while, a humid environment will make it solidify into a hard block, but if the bugs haven't gotten to it, it will be edible for a long time.
And of course, the best news is that a lot of wine will get better and better for the first few years (perhaps decades, in some cases) after the end of the world, as long as it is stored properly and isn't oxidized or turned to vinegar.
This problem as addressed in The Walking Dead:
In the Walking Dead comics, this issue finally came up in the A Larger World story line (issues #91-96). Incidentally, the TV show is currently in this very same story line (as of March 2016/the second half of season six). Rick notes that it has been about 2 years since the inevitable zombie apocalypse began, and most canned food is at or past its sell-by date. It appears that Rick (and writer Robert Kirkman) is under the same misapprehension as you are: he thinks "sell-by date" means "not safe after this date". As a result, he decides to ramp up farming activity at Alexandria.
The Walking Dead, Issue #91; A Larger World: Part I
As we have seen, Rick (and Kirkman) is simply wrong about expiration dates. However, he's right about needing to farm: the residents of Alexandria have been picking the surrounding area clean of food for 2 years now, and remaining supplies waiting to be scavenged are few and far between. Also, as mentioned above, although canned goods should remain safe to consume as long as the can is intact and not compromised, some of the nutritional content of the food (especially vitamin C) decreases over time.
The survivors can safely eat any canned food they find, as long as the cans are intact, uncompromised, and uncontaminated, and the food doesn't stink to high heaven when the can is opened. However, they will run out of canned food at some point, and even before they do run out, they will need other sources of food to maintain a healthy diet.