Metal content: Aluminum Pepsi cans.
I long ago learned that soda in plastic bottles loses its fizz after a few months because the CO2 slowly leaks right through the plastic, but I thought that soda in cans would keep "forever".
Last weekend I discovered a 12 pack carton of Pepsi I'd hidden behind some other stuff in a kitchen cabinet so the kids wouldn't find it and consume it all in minutes. When I went to remove it the carton was stuck to the cabinet floor and when I opened it about half the cans felt far lighter than they should and there was evidence of dried sugar on them and the carton.
I looked at the date code on the cans and gave myself a "dope slap" when I realized that the carton was about three years old.
I was curious about what Pepsi had to say about that and called their consumer line.
The lady I spoke to was quite prepared for the question, so I expect they hear about "old" cans leaking frequently.
The first thisg she told me was that drinking the Pepsi from a can which had leaked wouldn't kill me because the high acidity in the product prevented the growth of bacteria. So, I guess Pepsi is one of those "foods" like Honey and mayonaise which can stand being "opened" and then stored at room temperature without spoiling.
She said the high acidity was also the source of the leakage I'd found. The cans are lined with a coating which is intended to keep the product from touching the aluminum, but it isn't always perfect, and if there's the tinyist imperfection in the coating the Pepsi will corrode its way through the can, sometimes in as little as 6 months.
She also told me, "It only takes one." And that if one can in a carton develops a pinhole leak, a chain reaction takes place because the outside of the cans doesn't have that protective coating and if it gets wet with Pepsi it will corrode through faster than it will from the inside.
The bottom line is that Pepsi expects their cans not to leak by the "Best Taste if consumed by" date on them, but leakage after that date is not unheard of. (I didn't have the chutzpah to ask her for a "warranty replacement", nor did she volunteer one.)
I was curious to see where the leaks occurred and what they looked like so I took the least full unopened Pepsi can and punched a hole in the center of the bottom with a nail set. I shook out nearly all the remaining liquid and then pressurized the can with 10 psi air by squeezing a soft rubber washer between my air hose nozzle and the can.
I stuck the pressurized can under some water in a bucket and spotted a string of bubbles coming from a spot on the side of the can.
Looking at the can with a 10 power loupe I "thought" I could see a tiny white spot where the bubbles were coming from.
Sacrificing my 5 cent recycling deposit in the name of science I cut the can open.
Here's what I found:
It was sort of reminiscent of the leak which developed in a 3 inch long steel pipe nipple about 6 months after I used a couple of them to stand dielectric unions on the top of a replacement electric water heater I installed in our home. When I did that I didn't stop to think about the fact that the electrical feed's grounding of the heater and the code required grounding of our copper plumbing system would close the circuit and nullify the supposed benefit of using those fancy unions. Both nipples got severely clogged with rust and I discovered the problem when a pinhole leak punched through at the root of an exposed thread, which was the "thinest" part of the nipple.
Case closed...I think...