# How is a 25-year-old can of soda now empty without having been opened or poked? [closed]

I just discovered in my parents' basement a Sprite can from 1995* and also a Coca-Cola can probably from the same year.

Both cans are unopened and have no visible damage or holes. The Coca-Cola can feels "normal", but the Sprite can is empty!

You can hear in my video that there is no liquid sloshing around in it.

I can't find any way that the soda could have escaped.

We also don't see any mess near where the cans were, but I don't know for certain that the cans stayed in the same place for 25 years, so maybe there could have been a mess of liquid leaked out somewhere else if the cans had been stored somewhere else earlier. But nothing feels sticky or looks like there has been a leak of any kind.

What are possible explanations for how a carbonated drink could disappear from a sealed aluminum can?

*I had kept it as a "collector's item" from when the Houston Rockets won their second championship.

• I've removed somecomments that answered the question. Please use comments to clarify and improve a post. – rob Feb 23 at 21:52
• My comment that was removed did not answer the question, it was meant to clarify and improve the post. So again, put the can into a bucket of water and see if air bubbles come out at the spot where the can is usually opened when you squeeze it slightly. That would answer the question if we knew if bubbles came out, but we don't know that yet – Yukterez Feb 23 at 22:43
• @Yukterez After allowing more time for some more answers that don't require me doing anything to do the can, I'll be interested to squeeze it under water, like you suggest. – Ryan Feb 23 at 23:29
• Did you inspect for pin holes? You say you knew it to be a "collector's item." There are people out there who get serious about collecting beverage cans, and they often will empty a can by poking a tiny pin-hole in some place, usually on the bottom, where it's hard to notice. Then they shake the can so that the evolved $CO_2$ will blow all the liquid out. Maybe your parents had a friend who showed them that trick. – Solomon Slow Feb 24 at 1:11
• – nhahtdh Feb 24 at 6:32

The soda can't escape through a sealed can, which leaves two options: the can wasn't sealed or the soda didn't escape.

## Soda didn't escape:

This is the less likely and less interesting case: the can was produced defective and never had any soda in it. Issue on the manufacturing line, and whoever saved it (you/parents?) did so because that was novel, and subsequently forgot.

## Can wasn't sealed:

Again, a manufacturing defect is certainly possible, and in the intervening years most of the contents escaped through a defect you can't see, probably around the lid or the pop tab itself.

This requires a serious molar flux through the hole. I needed to prove to myself that it was possible. Using Fick's First Law of diffusion, $$J = -D\times \frac{\delta C}{\delta x}$$

• A temperature of $$20\ \mathrm{^\circ C}$$
• Which leads to a density of air of $$1.204\ \mathrm{kg/m^3}$$, or $$0.1204 \ \mathrm{g/cm^3}$$
• And a partial pressure of water of $$0.0231$$
• And a diffusion coefficient of water vapor in air of $$0.242\ \mathrm{cm^2/s}$$
• About $$6\ \mathrm{cm}$$ as the distance, given that the can is on average half full and the storage space was very dry

We get a flux of $$0.004856\ \mathrm{g/(cm^2\ s)}$$

Given that $$12\ \text{fl.oz.}$$ is roughly $$355\ \mathrm{cm^3}$$ (and the soda is mostly water which is roughly $$1\ \mathrm{g/cm^3}$$ at that temperature), that means that a water vapor leak through the top over a period of $$25$$ years ($$7.88\times10^8$$ seconds) would only need to be a $$0.1\ \mathrm{mm}$$ square hole.

That's $$1{-}2$$ times the thickness of a human hair, on average. I couldn't see that hole, especially in the region under the pop tab. We could say the can was nearly fully empty the whole time and that the room wasn't that dry, with $$50%$$ relative humidity, and the hole would still only have to be $$0.2\ \mathrm{mm}$$ on a side.

## Can wasn't sealed: (part 2)

The other answer, which I admit I was going to present when the above answer required too big of a hole, is that the fluid escaped as a liquid rather than a gas. Water has strong adhesion and cohesion, and will tend to "wet" any surface it is in contact with. If there was the tiniest hole or crack for water to flow through, it would have done so and evaporated long ago.

## As an aside:

Interestingly, colas generally contain phosphoric acid, while sprite has citric acid, which is much weaker (and both have carbonic acid, weakest yet). That means that coke is more likely to corrode a metal container, enlargening a hole. However, aluminum is wonderfully inert in this capacity, and rapidly forms a persistent, impervious layer of aluminum oxide only a couple of atoms thick which prevents any further corrosion, so the sodas should not be chemically etching the can in any appreciable way.

## Testing:

As mentioned in a comment above, you can do the bubble test yourself fairly easily. You can even enhance the test by precooling the can (and air inside) and placing it in warm water, creating a pressure difference. You might be able to see bubbles coming up.

For a really definitive leak test, you can have the container tested using a radioactive tracer gas. Businesses exist to do just this, usually connected with the semiconductor industry. They can calculate the exact size of the hole, but such a service isn't free.

• Shouldn't $J = -D\times \frac{\delta C}{\delta x}$ actually be $J = -D\times \frac{\mathrm{d} C}{\mathrm{d} x}$? $\delta$ normally means variation, while Fick's law involves derivative. – Ruslan Feb 24 at 8:09
• Coke cans have a plastic film on the inside; the aluminium doesn't come into contact with the drink. The aluminium wouldn't corrode into aluminium oxide, it forms aluminium phosphates (and free hydroge) in contact with the phosphoric acid. – Luaan Feb 24 at 11:41
• You had mentioned a square hole that was 0.1 to 0.2 mm on a side. Is it possible there are numerous, much smaller holes, with areas that add up to 0.1 to 0.2 mm? – Randall Stewart Feb 24 at 13:23
• If the water escaped as a gas, the can plus the sugar and other ingredients left behind should weigh considerably more than an empty can. – StackOverthrow Feb 24 at 16:43
• Worth pointing out that if there is a hole it is most likely at the base of the tab. Take any unopened can of pop and you can pull slightly on the tab without too much force to break the seal, without any visible indication. Also, if the OP really wants to know and opens the can, presumably there would be plenty of sugar residue inside still that would be immediately visible. – Kai Feb 24 at 18:39

I’ve had numerous experiences with unopened old cans of soda losing part of their contents, though my cans were no where near as old as yours. I do remember one being empty.

The snap top tabs probably don’t make a perfect seal. That combined with the positive pressure of the carbonation might result in very slow escape of the carbon dioxide gas, probably also increasing the size of the leak. Thereafter there’s probably slow evaporation of the contents over many years.

Why the Coca Cola cans didn’t also lose all the liquid is another matter. But coke has a reputation for being very acidic. People are known to use it as a cleaner. I also read it interacts with aluminum causing corrosion. Just a guess but perhaps corrosion somehow improves the seal of the snap tab. A corroded bolt is harder to remove.

Hope this helps.

• Or perhaps CocCola csns have an extra protective layer inside. – S. McGrew Feb 23 at 22:58
• @S.McGrew Perhaps. Perhaps they anticipated the outgassing problem. – Bob D Feb 23 at 23:01
• A protective layer would make sense, not just for the outgassing but to protect the metal from the acid. Aluminium isn't very toxic, but you still want to avoid unnecessary consumption. – MSalters Feb 24 at 9:08
• @MSalters did a little research. Looks like all soda cans are polymer coated inside because most sodas are acidic. It appears Coca-Cola classic is the most acidic with ph 2.4. Sprite is 3.3 so not sure coating is reason coke survived – Bob D Feb 24 at 9:28
• @BobD It's not about how acidic the contents are, it's about the acids involved. Coca-Cola contains phosphoric acid, which reacts with aluminium to form aluminium phosphates (toxic) and hydrogen gas. – Luaan Feb 24 at 11:46

This also happened to me with an unopened 7up can from 1993 which I had stored in my collection. When the can was about 6 years old I found it looking intact but feeling completely empty; underneath and around it was a small puddle of sticky clear goo, hinting that its contents had very slowly leaked through a tiny, indiscernible hole somewhere along the can's bottom. The water probably evaporated during the process leaving just the syrup. It's very likely that the same happened to you, except that in your case the can was untouched for 25 years - surely enough time for the members of some lucky ant colony to loot the fine tasting sugary goo and disappear without a trace.

• Interesting story and ideas! Thanks. – Ryan Feb 24 at 17:11
• Given that the evaporation idea requires a too large hole and that Ryan insists the can was not empty, I find this the most believable scenario (also, it is possible the can was simply moved). – Void Feb 24 at 17:14
• Yes, this happened to me as well. I thought the universe had played a trick on me personally, I'm relieved to hear that it's a real thing. – uhoh Feb 26 at 1:33

My vote would be that a defect in the crimp seal between the top and the can wall is more likely a culprit than a defect around the tab. The tab after all is a 'tear' mechanism, a weakness is pressed into an aluminium sheet and a 'button' pressed into it as well that is used to anchor the ring whereas the seal between the top and the can wall has some rubbery stuff in cans I've taken to pieces. Wherever the fault, a failure to properly seal the lid to the can wall or a hole torn into the lid while pressing the weakness or attaching the ring pull means that the contents can escape. If the can was stored with such a leak at a low point then the contents would be pushed out initially by the CO2 and once any CO2 overpressure was exhausted, temperature changes would blow liquid out / suck air in. If the can wasn't stored with the leak at a low point, temperature changes would tend to suck in ambient (dry-ish) air and expel saturated air. Over time (25 years...) that would evaporate the liquid. I've had a whole batch of small cans (of S... Tonic Water) do that to various degrees over less than 10 years. Some leaked to dryness, some leaked to mostly-empty. Oh, and they'd all leaked the gas out so none were under pressure.

My vote is that the can was accidentally shipped empty. This does actually happen - I myself happen to have a nearly-brand-new unopened Pepsi can which is empty (and I once encountered another, but I foolishly opened it to confirm the fact, thus rendering it just another empty can). I also have an old tub of Wendy's honey-mustard dipping sauce which also was shipped sealed empty, and a sealed Life-Saver packet with no Life-Saver in it. I like to collect 'naturally-occurring' defects of this sort.

• bit of a coincidence though for such an old can to be also a defective one? – Andrew Steane Feb 24 at 13:47
• It was full originally. – Ryan Feb 24 at 14:00
• @AndrewSteane Not necessarily - that might be the only reason someone held onto it for that long. – Darrel Hoffman Feb 24 at 14:30

The more likely explanation of any of the described scenarios is probably in the realm of corrosion chemistry.

In time, the protective Al coating is penetrated in the presence of dissolved salts.

The highly reactive exposed Aluminum will chemically react (even with the water content, not too mention any acids presence including carbonic or phosphoric, found in select brands):

2 Al + 6 H2O -> 2 Al(OH)3 + 3 H2 (g)

This will further create pressure.

The form of the attack most likely results in so-called pit corrosion. To quote a source:

Corrosion of aluminum in the passive range is localized, usually manifested by random formation of pits. The pitting-potential principle establishes the conditions under which metals in the passive state are subject to corrosion by pitting. Pitting corrosion is very similar to crevice corrosion.

As a pinhole leak (or leaks) from a pressurized can empty the contents of a soda can, it may further leave the false impression that it was always empty.

• Absent something attacking the oxide, wouldn't aluminum form a protective oxide and prevent corrosion more than a few atomic layers deep? Aluminum is fairly famous for this property. – Bartimaeus Feb 26 at 6:32

As others have said, more than likely it was never full in the first place. My grandfather worked for a can manufacturing company and had a large collection of empty sealed beer cans of all different brands. Your can could have been a reject or more likely just a sample.

• This may be true for other people, but my family and I have no memory of a sealed empty can in this case. We're nearly positive that we bought a full can and shelved it and then found it empty 25 years later. – Ryan Feb 24 at 16:18