How to Make Time Bomb Sodas
In both instances, there was no explosion of carbonation.
It seemed like speed of exposure was critical. Even if half of the Coke was exposed to half of the mint, the effect was seriously subdued.
It was a bust.
With this new perspective, I had some new ideas. I could use dry ice or liquid nitrogen to freeze a very thin shell of water around the Mentos without dissolving the surface. I could modify a drinking straw to form a temporary air-tight chamber underwater to hold a mentos. I could refine my hollow ice-cube technique to hold two or more mentos.
However, none of this is necessary. There is already an excellent technique for serving time bomb sodas. As far as pranks go, it is pretty much perfect. I learned about it reading Mischief Maker's Manual by John Hargrave.
Instead of serving Coke in a glass, use smaller Coke bottles, available in 12 and 16oz sizes with a screw top concealing a hidden Mentos in the neck of the bottle. When the bottle is opened, the suspension is broken, dropping the candy into the soda just as the lid is removed. Here are some photos:
Use a sewing needle to poke a thread through a Mentos candy. Use a thimble or impale the Mentos onto the needle to pierce the candy shell.
Pull a black thread through, leaving at least two inches on either side of the candy. I used white thread for illustrative purposes.
Once you find yourself threading Mentos in the kitchen, you might as well thread a bunch of them. They are extremely useful.
Open a new coke and suspend the threaded candy in the mouth of the bottle.
Holding the threads gently, slowly screw the cap shut. You can let the threads loose as soon as the cap begins to tighten.
Snip off the excess thread.
Use nail clippers for an extremely close snip, but don't worry about it much. Superman himself wouldn't notice these threads. The arrangement is invisible, hidden just under the bottlecap.
Serve cold, or just leave the bottle in the break room fridge at work.
When the bottle is opened, the thread comes loose and drops the Mentos into the Coke. It's the perfect height and situation for the maximum foamy effect. It is perfect!
When I tested it, in the aftermath the bottle was blown out nearly empty. It was hilariously lightweight afterward. Which is good, because your guest is fairly likely to chuck that bottle towards your face.