What causes food to spoil in a can?

The most common causes are container failure (rust from damp storage, dents that bend the seam, or scratches that expose bare steel), under-processing (the original heat step missed a few heat-tolerant spores), and chemical reactions between the food and the can lining over many years. Storage above about 35°C (95°F) accelerates all of these and can also wake up thermophilic spores that survived processing.

Is canned food really sterile?

Not absolutely. Properly canned food is “commercially sterile,” meaning the heat treatment has destroyed every microorganism that could grow and cause illness or spoilage under normal storage conditions. A few extremely heat-resistant thermophilic spores can survive, but they only germinate at temperatures above roughly 45–55°C (113–131°F), well outside any sensible pantry.

Does canned food expire?

The dates stamped on cans are “best by” or “use by” dates that indicate peak quality, not safety. The USDA states that a commercially canned product with an intact seal, kept in cool, clean, dry storage, is safe to eat indefinitely; flavor, color, and texture will, however, slowly decline. Discard any can that is leaking, bulging, deeply dented at the seams, or that hisses or spurts when opened.

What temperature kills bacteria in canned food?

High-acid foods (pH below 4.6) like tomatoes, fruit, and pickles can be safely processed in a boiling water bath at 100°C (212°F). Low-acid foods such as meat, beans, and most vegetables have to be processed in a pressure canner at about 116–121°C (240–250°F), because the spores of Clostridium botulinum , the bacterium that causes botulism, can survive ordinary boiling water but not those higher temperatures.

What Causes Canned Food To Spoil Eventually?

Q: Why does canned food last so long?

After the can is sealed it is heated, which kills the bacteria, molds, and most spores that would otherwise spoil the food. Because the seal is airtight, nothing new can get in, so the food inside is what food scientists call “commercially sterile.” In a sealed, undamaged can stored in a cool, dry place, low-acid foods like meat, beans, and vegetables typically stay safe to eat for 2 to 5 years, and high-acid foods like tomatoes and fruit for about 12 to 18 months.

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Why Does Canned Food Last So Long?
How Does Canned Food Eventually Go Bad?

A sealed, undamaged can of food is “commercially sterile,” so it stays safe to eat for years: low-acid foods (meat, beans, vegetables) keep 2 to 5 years, high-acid ones (tomatoes, fruit) about 12 to 18 months. Cans eventually spoil when rust, dents, or hot storage compromise the seal, letting microbes back in or causing slow chemical reactions that change flavor.

For anyone who has ever had a sliver of fear about a holocaust of any kind – nuclear, zombie or otherwise – canned food has always been a logical choice to put in your survival bunker. In every movie about people surviving the end of the world, canned food plays a major part. For those less worried about the end of days, canned food is also an excellent choice for camping and long-term storage in forgotten pantries.

However, what many people don’t realize is that canned food doesn’t always last forever. Canned food lasting for 5 years, or even a decade, is entirely possible, but a number of factors can eventually make that canned food spoil. The question is, why can’t it last forever? What can eventually make canned food go bad?

What Causes Canned Food To Spoil Eventually?

Short Answer: A properly sealed can of food stays safe for years: low-acid foods (meat, beans, vegetables) for 2 to 5 years, high-acid ones (tomatoes, fruit) for 12 to 18 months. Rust, dents, or hot storage are what eventually let it spoil.

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Why Does Canned Food Last So Long?

When food is canned, it is loaded into a brand-new, clean can and then sealed. The food is initially passed through rigorous quality testing, but there is a final step where all the magic happens. The fully sealed can is then heated so the food inside becomes cooked. When bacteria and other nasty pathogens are heated beyond a certain temperature, they are neutralized or killed. High-acid foods like tomatoes, fruit, and pickles can be safely processed in a boiling water bath at 100°C (212°F), but low-acid foods like meat, beans, and most vegetables have to go into a pressure canner at 116–121°C (240–250°F). The reason is Clostridium botulinum, the bacterium behind botulism: its heat-tolerant spores can survive ordinary boiling water but not those higher temperatures. Since the can is sealed before this heating step, no additional bacteria or spores can make it inside. Therefore, when you open it up a few months, years, or decades later, the food should still be relatively fresh.

Food spoils because microorganisms come into contact with the food, either through the air or something else touching the food. These tiny organisms, like bacteria or fungi, need to eat, just like humans and every other living creature. Since they are on a food source, they begin to eat immediately, and just like every other creature, they need to eliminate waste products. The waste products from microorganisms cannot be metabolized by human beings, and often have a foul taste, which we then label as being “spoiled”. By eliminating those microorganisms, as the canning process does, there can’t be much of a change in the quality or composition of the food.

However, there is a bit more to the story….

How Does Canned Food Eventually Go Bad?

Despite your best intentions, and the best-designed fallout shelter food supply, there are some factors that can affect the quality of canned food. If your underground bunker or basement pantry is damp, or if the cans get wet, oxidation of the bare steel can cause the can to begin to rust. Even if the can doesn’t rust “through”, that oxidation process can open the doorway for microorganisms to enter the food inside. At that point, the feast begins, and the food will eventually spoil and go bad, albeit slowly.

If a can is damaged, bent or dropped, it can compromise the airtight seal of the can, making it easier for microorganisms to enter the can. Furthermore, despite the sterilization process, some foods can still contain dormant spores of microorganisms that aren’t completely eliminated. If the can is exposed to sunlight (which is heat), the air inside the can will begin to expand, and that temperature increase makes an ideal environment for the microorganisms to begin to thrive and multiply. This isn’t common, but it can certainly happen. Make sure to keep canned food in cool, dry and dark places.

Some foods will eventually begin to break down and experience chemical reactions between its component parts, particularly in highly acidic foods. While this isn’t the same as traditional spoiling, it can change the flavor and taste of the food, making it unpalatable when you finally open it up on your camping trip. This won’t make you sick, necessarily, but it won’t make for a pleasant dining experience.

What Causes Canned Food To Spoil Eventually?

Finally, there isn’t a 100% guarantee that the sterilization and canning processes will prevent any microorganisms from being present in the cans. Canned food manufacturers have extremely stringent regulatory processes, but at-home canning methods (which are becoming increasingly popular) are far from perfect.

If you want to keep yourself safe from any food-borne pathogens or spoiled food, just use your common sense. First, inspect the appearance and integrity of the can. If that looks okay, open up the can and see if there are any visible signs of microorganisms growing on the surface of the food or lid of the can. Passing that test, give the food a sniff. Lastly, taste the food to see if it seems normal. If there is any doubt in your mind at any point in that process, toss the can. Most canned food is rather inexpensive, even if you do it yourself, and who can put a price on staying healthy!?

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