CarbonationFilter! How long would it take for an unopened can of soda pop to go flat? Would it ever?

February 14, 2008 5:45 PM

CarbonationFilter! How long would it take for an unopened can of soda pop to go flat? Would it ever?

So I'm reading Cormac McCarthy's The Road, which all takes place in some vaguely defined post-apocalyptic setting that seems to be the aftermath of a nuclear war, and there's a scene where the main character finds a can of Coke and gives it to his son. The father first pops the top and sniffs it, and carbonation tickles his nose. The book doesn't specify exactly how long ago the war was, but -- given that the kid was born days after it happened, and now seems to be six or seven -- well, that Coke's about six or seven years old. That it still hasn't gone flat doesn't strike me as impossible, but it does make me wonder how long a sealed can of soda pop would retain its carbonated properties. Anybody?

posted by kittens for breakfast to science & nature (25 comments total)

If it's still in a sealed container, it's still carbonated.
posted by sanka at 5:48 PM on February 14, 2008 [1 favorite]

If the can is perfectly sealed, I think it'd stay carbonated forever. If there's nowhere for the gas to escape, and the air in the can is already saturated, then it would stay fizzy.

I have no idea how perfect the seals on cans are though... presumably good enough to last many months, but I doubt the manufacturers would go to great lengths to ensure years of fizziness.
posted by twirlypen at 5:49 PM on February 14, 2008

I would say years. Aluminum is very resistant to oxidation/rusting, and there's a plastic sealant 'bag' on the inside of the can to keep the acidic soda from eating its way out of the can.
posted by onalark at 5:53 PM on February 14, 2008

Last year I had a bottle of Coke that had been boarded up in a store since 1974. It tasted great.
posted by dobbs at 5:54 PM on February 14, 2008 [7 favorites]

Actually, I think that's probably the best answer. Ah...what the hell...
posted by kittens for breakfast at 5:54 PM on February 14, 2008

It may fizz, but it can taste like CRAP. I was just at a friend's house and had a Diet Coke that was (unbeknownst to me) purchased around 2002. It tasted horribly chemically and we dumped it out instantly.
posted by GaelFC at 5:56 PM on February 14, 2008

If the can survived intact, which is tough to imagine in a post-apocalyptic wasteland, but not unimaginable if kept safely in a cool, dry, cupboard, soda would be fine.

there was a metafilter post about somebody auctioning off crystal pepsi And some guy named spilion claims to have unopened OK Cola from 1994. I think its possible if the can isn't abused.
posted by OldReliable at 5:57 PM on February 14, 2008

Soda has expiration dates on it. I don't know if it loses its fizziness specifically, but it does go bad. Regular soda lasts longer than diet, but either way, it's not years. Diet soda lasts about 6 months I think.

(Reason I know this: A couple years ago, I found out that Coke was planning to stop making Diet Vanilla Coke, which I LOVED with the white hot passion of a thousand suns. Soooo, I spent the month I had left stopping at different grocery stores whenever I could and amassing about 40 cases of it, thinking I could ration it out and it would last me two years. Then I read about expiration dates on soda. I had to drink it all in about 4 months.)
posted by clh at 5:59 PM on February 14, 2008

If the can survived intact, which is tough to imagine in a post-apocalyptic wasteland, but not unimaginable if kept safely in a cool, dry, cupboard, soda would be fine.

Yeah, the can was way up in the guts of a junked soda machine. I imagine the machine could shield it from harm.
posted by kittens for breakfast at 6:00 PM on February 14, 2008

Soda has expiration dates on it. I don't know if it loses its fizziness specifically, but it does go bad. Regular soda lasts longer than diet, but either way, it's not years. Diet soda lasts about 6 months I think.

Interesting...given what you and GaelFC said, and weighing it against dobbs's testimonial about the thirty-four-year-old (!) Coke, I have to wonder whether they just don't make the stuff the way they used to....
posted by kittens for breakfast at 6:03 PM on February 14, 2008

I've routinely encountered expired sodas at my old office job. We used to order cases in bulk for meetings, and then keep them in a locked drawer to avoid pilfering. They could sit around past their expiration. Diet sodas, as mentioned above, went off at around the six month mark. It had a bad taste, and while still carbonated, it was not as "sparkly" as usual.

Regular sodas did last longer, but the first sign that something was off was that they were also a bit flattish. This would be at around a year past the good by date. i don't know how long it would take to go completely flat, but I have doubts about enough carbonation to "tickle" ones nose.
posted by kimdog at 6:08 PM on February 14, 2008

Well, in fairness to Mr. McCarthy, I just looked back to the scene and found the exact phrase: "He leaned his nose to the slight fizz coming from the can." So that's maybe not a tickle so much as kind of...um...a misting?
posted by kittens for breakfast at 6:14 PM on February 14, 2008

Diet soda expires because the artificial sweetener aspartame breaks down over time. Once they started putting expiration dates on diet soda, though, consumers started asking why there weren't expiration dates on regular soda too, so they put them on there. But sugar doesn't break down, so dates on non-diet soda are basically marketing.
posted by kindall at 6:16 PM on February 14, 2008 [1 favorite]

They DON'T make sodas the way they used to.
To save untold millions of dollars, Coke switched its sweetener from sugar to corn syrup years ago.
Purists still argue about the taste differences.
And I'm told artificial sweeteners are very unstable, which led Pepsi to inaugurate that "best by...' stamp on their products.
I always thought it a cynical ploy, but my step-father assures me that "expired" Diet pepsi is heinous...
posted by Dizzy at 6:18 PM on February 14, 2008 [1 favorite]

(Should've previewed! Apologies!)
posted by Dizzy at 6:19 PM on February 14, 2008

Along the same lines, I got a coke out of a machine a couple days ago and thought it was possibly frozen. The can was slightly dented like you'd sucked the air out, but it was still totally full. When I opened it, it was totally flat.
posted by CwgrlUp at 6:21 PM on February 14, 2008

I can testify that heat will definitely hasten the diet-soda-going-bad process.
posted by blenderfish at 6:22 PM on February 14, 2008

But sugar doesn't break down

Will it oxidize? (Assuming some oxygen leaks into the can)
posted by blenderfish at 6:26 PM on February 14, 2008

I have several glass thermos bottles nearly a hundred years old with quite good vacuums yet-- and several others which have lost theirs though they appear to be perfectly intact.

I have my doubts about modern aluminum cans because the lids look like they are merely pressed on (which would mean liquid metal did not flow around the area of the seal), and because to make them pop-top, they have to cut a deep grove around the pull ring, leaving the metal there almost foil thin.
posted by jamjam at 6:26 PM on February 14, 2008

To save untold millions of dollars, Coke switched its sweetener from sugar to corn syrup years ago.
Purists still argue about the taste differences.

Oh, it's not a purist thing, it actually does taste CONSIDERABLY better. Brighter, more lemony, better mouthfeel. I'm talking regular Coke with sugar (usually brought back in vast quantities whenever I visit Canada) vs. American diet Coke.

Also, I've got cans of flavored seltzer that have been in the basement over a year (I hoard those, too, whenever I go back to Massachusetts, as you can't get Polar brand vanilla water here) and they've all been just fine carbonation- and flavor-wise.
posted by bitter-girl.com at 9:05 PM on February 14, 2008

Will it oxidize? (Assuming some oxygen leaks into the can)

Dude, the can's got positive internal pressure, so if the can does leak, 1). stuff is leaking out before it's leaking in, and 2). oxidized ingredients are the least of your worries.
posted by SlyBevel at 9:07 PM on February 14, 2008

Contrary to what many people here have written, I have *twice* put a 12-can package of Diet Coke in the trunk of my car, and found it many months later - both times over summer. And both times, most of the cans were, amazingly, empty when I took them out of the trunk. No stain residue as if they had exploded. In fact, the cans were still unopened. A few had very mild traces of Diet Coke color around the pull-tab. I can only imagine that something in the summer heat in the trunk forced microscopic openings on the part of the can that opens. But who knows? No one's ever provided a very good explanation for this phenomenon.
posted by Dee Xtrovert at 1:12 AM on February 15, 2008

I've accidentally frozen some soda's which didn't rupture the can. When I opened them they were already about 75% flat.
posted by whoda at 5:14 AM on February 15, 2008

In my grandparents house there was a second refrigerator in the basement, that was used for sodas and whatnot. Many of these products were purchased when they were on sale and as such there were often sodas several years old in there. Let me tell you that they were NASTY, and flat and gross.
posted by BobbyDigital at 9:44 AM on February 15, 2008

AskMeFi never fails to inform. Just the other day I was looking at an unopened can of Coke I bought in Japan in 1983 (because everything, except the COKE script, was in Japanese). And I was wondering whether the coke was still good. Not that I'd try it.
posted by Taken Outtacontext at 10:23 AM on February 15, 2008