How to Make Time Bomb Sodas
I also tested whether Mentos would still excite the carbonation in a glass of Coke if they were wet.
I caught this test on video. June dropped three Mentos into water, then quickly fished them out and dropped them into a cup of Coke. They worked well.
The quick exposure to water didn't ruin the surface, so there was still hope that a container of ice could be created if the engineering was right.
I started with the hollow ice cube scheme, because it would take the most freezer time to execute. I filled a few shot glasses with water, gave them about an hour to freeze on their perimeter, then cracked the top and poured out the remaining water. Then I put them back into the freezer.
After this tiny ice cup was rock solid, I dropped a mentos into each and inverted them onto a shallow bowl of cold water. If executed properly, this would seal the top of the cup. I consider myself something of an ice craftsman, having triumphed over adversity in creating the frozen six-pack holder.
I was able to utilize the tiny ledge inside to keep the Mentos up out of this sealing water. The Mentos would be sealed in, almost completely dry.
More on the hollow ice bombs later.
Wrapping a Mentos with breath strips was challenging. They wouldn't stick while dry, but with too much water they dissolve into a sticky green mess. With practice I managed to create a solid shell of strips.
The strips are gelatin, so in theory they should dissolve in Coke, leaving an explosive Mentos at the bottom of the cup to react with the Coke.
It didn't work. It bubbled a bit, but not so much that you'd even notice if you weren't watching for the effect.
I'm not sure what went wrong, but I believe that the gelatin shell dissolved slowly, so the Mentos was slowly exposed to the Coke, limiting the amount of reactive surface area available at any one time. By the time the whole Mentos was exposed, most of the soda-borne carbonation had been released.
The Mentos shielded by Gummi bears failed similarly.
The effect was an above-average number of bubbles for a minute, followed by nothing.
What I needed was an instant or nearly-instant introduction of the Mentos surface to the Coke bath.
Two of the hollow Mentos ice bombs looked fantastic! In the case of the third one, I tried to jam two Mentos inside, and ended up cracking through the fragile shell. I was eager to test them.
Despite every other time-release method falling short, I couldn't see how these were going to fail. Armed with a fresh glass of Coke, we dropped one in! It floated magnificently, quickly melting in the uncooled Coke. It fizzed quite a bit as the shell was breached and Coke began to seep inside. Ideally, the bottom would have melted first, dropping the dry mentos right to the bottom of the glass, but it didn't always work that way (we tried twice). The shape of the ice cube rotated on top of the coke, finding a new center of gravity as the lower section melted.