My son asked for an exploding cake for his birthday
May 23, 2015 2:54 PM   Subscribe

I'm looking for suggestions on how to make this happen.

I definitely want to do something cooler than baking soda / diet coke or baking soda / vinegar, or sparklers. I don't think it will qualify to him as "exploding" unless bits of cake are flying. Of course however I do this, I understand it will need to be outdoors, with lots of adult supervision, and the little guy at a safe distance.
posted by unstrungharp to Food & Drink (16 answers total) 9 users marked this as a favorite
I think it was on tumblr somewhere - put frosting on a balloon so it looks like a cake. You'd have to let him cut it with the knife to make it explode. (And then bring out the normal cake.) Here's a random YouTube example.
posted by artychoke at 3:02 PM on May 23, 2015

There's also the idea of a pinata cake. You could go cake-cake or fake-cake. If you go the fake cake option you could even mix pop rocks into the chocolate so that it explodes and crackles when you eat it, which could be a cool effect. It's not properly an exploding cake, but it might be an idea you can incorporate into the final design.

I wonder if you could shove a few M80s in a cake, hide them with frosting, then light the fuses like they were candles...
posted by phunniemee at 3:11 PM on May 23, 2015 [4 favorites]

For my son's birthday one year, my boyfriend bought a $5 supermarket cake, threaded together a "wreath" of small firecrackers on top with fuse-material, set the cake up on some sawhorses in my parents' backyard, then lit it up. It was AWESOME.
posted by julthumbscrew at 3:26 PM on May 23, 2015 [6 favorites]

Yikes - this is one of those questions where the most impressive answers come with significant risk. Whatever you wind up doing, wear safety glasses! Really, go out and buy some if you don't own a pair.

Assuming pre-made firecrackers are either illegal or intimidating, and potentially dangerous chemistry is off limits, the best reasonably safe idea I can think of is to use party poppers. Bake a cake half an inch taller than the poppers, flip it upside down, then burrow a bunch of party popper sized holes in the back. Stick the poppers in place with the nibs facing up. Then over the top of that place a plank of wood (or several sheets of very sturdy thick cardboard, or something similar) which has holes drilled in the same pattern large enough for the nibs of the poppers to stick through. Use string to tie all the pull cords together into a bundle. Flip the whole thing over to ice and decorate it. Then set it on blocks so you can reach under and pull down on the cord bundle. It's probably worth testing this on a smaller sample cake well before the big event, and it might be a good idea not to leave the poppers in the cake for too long ahead of time, as they'll soak up moisture and eventually stop working.

(Dry ice in a plastic bottle buried in the cake is the other obvious choice. It would be slightly more spectacular but far more dangerous. I'd be willing to do it myself, but can't in good conscience recommend someone else do so. In case you do go that route, remember that dry ice bombs can go off far more quickly than you expect and they can do very real damage to people. Absolutely wear safety glasses and set things up so you can run far away the second you finish fastening the cap.)
posted by eotvos at 3:32 PM on May 23, 2015

A less dangerous option might be to get one of those foot-powered rockets (like this one) and attach the pump from the bottom to a balloon hidden inside the cake. I'd probably also put some cardboard on top of the balloon to make sure when you stomp on the pump the cake really goes flying.
posted by Poldo at 3:48 PM on May 23, 2015 [2 favorites]

Explosions can be mechanical instead of chemical.

Any kind of spring-loaded expanding thing covered with a layer of cake and frosting qualifies. Yeah, that chemical bang is satisfying, flying, low-velocity cake is where the spectacle is at. I would suggest something like a circular region of cake supported by wedges of plastic or cardboard, and the cake is cut into the same wedges. The frosting layer hides the cuts. The supporting layer's wedges are hinged (with something as simple as tape) to the base. The whole thing sits on a spring-loaded piston which shoves the center of the wedges upwards, resulting in maybe 6-8 cake-catapults. Cakeapults.

Alternate: something heavy, like bowling-ball heavy, dropped into a cake with some hidden levers. Ball drops through center (splat!), cake is hurdled up and over the center with random energy.

Eye protection for all, plz. Goggles adds some ceremony to the whole thing, and has the side benefit of keeping icing and debris out of young eyes. Crying at parties sucks, even if it is your party and you want to cry. Goggles are cheap (especially when there's no caustic danger, unless you've got some chemical action going on, and everything's low-velocity), eyes and memories are priceless.
posted by Sunburnt at 4:55 PM on May 23, 2015 [2 favorites]

You might try a mylar balloon, electric solenoid valve, and small compressed air cylinder with a schrader valve. Plumb them together in the obvious fashion, and charge the cylinder to an appropriate pressure (no more than 10 PSI, I suspect).

Insert the mylar balloon, folded in such a fashion that it will expand radially when inflated, into the center of the already-baked cake. When you electrically operate the solenoid valve, the balloon will inflate suddenly, and toss the cake radially. Irrigation sprinkler valves work fine as solenoid air valves.

You might want to test-drive this a few times. A bursting mylar balloon is punishingly loud, so you could avoid it entirely by calibrating your compressed air cylinder's initial pressure.

>Dry ice in a plastic bottle buried in the cake is the other obvious choice.

Don't do this, under any circumstances. The burst pressure of a PET plastic bottle is quite high, the timing is unpredicable, the sound is damagingly loud, and it generates shrapnel that cannot be seen with x-rays. The energy involved is too great for safety, where children are concerned.
posted by the Real Dan at 5:01 PM on May 23, 2015

Buy a set of Stomp Rockets. Attach a thick balloon to the end of the launcher hose. Insert balloon into middle of cake. Stomp.

On actually reading the comments: exactly what poldo said.
posted by bondcliff at 6:42 PM on May 23, 2015

I'm not sure if you'd get pieces of cake flying around, but you could rig something with mentos and diet coke that would be quite dramatic.
posted by MexicanYenta at 7:48 PM on May 23, 2015

I don't suppose your kid is a fan of mysteries? You can always rig up a fake "Mission Impossible" style bomb timer. :D

I like the balloon idea, but I have a much easier "detonation" solution... Ever tried a "lancet"? One of those used for finger prick testing? You may be able to rig something under the cake itself or along the side. Set it to maximum prick (longest extension), cock it, then click, and BLAM! Balloon goes poof. And since the lancet retracts it's relatively safe until you can retrieve it. Obviously you'll need to test a few setups to find one that works.
posted by kschang at 9:29 PM on May 23, 2015

Best answer: I'm reminded of a prank we used to play in the lab: put a little chip of dry ice in a microcentrifuge tube and slide it under someone's stool. After a few minutes, bang! (A microcentrifuge tube is like a small plastic test tube, the size and shape of a bullet, with a snap cap.) Unlike more serious dry ice bombs, these wouldn't build up very much pressure before the cap snapped open but they'd make a satisfying *crack* when they did. (Considerate people would make sure the victim wasn't working on anything sensitive at the time.)

So in my mind I'm thinking of a cake with a hollow cut in the bottom, which could be filled by a tupperware (or whatever) plastic container filled with a little dry ice and warm water to help it sublimate more quickly. The tupperware "charge" would be loaded lid-down and maybe that part of the cake has no actual cake, just a heavy decoration, on top of it. Also the cake has been pre-cut along fragmentation lines that are hidden under the frosting.

When the time comes the dry-ice charge is loaded under the cake, everyone waits with excitement, then *bang* it suddenly, but safely, flies apart a few inches (or however wide you want the bits to go -- I'm thinking a scenario where you can eat the cake afterwards.)

In my mind I think it'd work, with a big sheet of plastic spread out to catch the pieces, but the tricky part would be experimenting with different sizes of plastic containers, amounts of dry ice, and tightness of lids; all to dial in just the right amount of bang. *Then* it would mean baking at least one test cake to experiment with the rest of the effect. But when properly dialed in I think it would reliably produce a pretty dramatic exploding-cake effect that would be food safe, child-eyeball safe, and edible afterward.

(And agreeing with the above safety warning: dry ice bombs that wait for the container to burst, instead of a lid popping open, are much more dangerous -- even their sound is loud enough for permanent hearing damage -- so make sure you're not creating that type of charge.)
posted by traveler_ at 1:29 AM on May 24, 2015 [1 favorite]

Presto. Do it with a balloon and a cereal box. You could probably get it flatter than the one in the picture by using a few rubber bands to strap it down. For extra oomph, put some baking powder in the balloon before you blow it up. When it explodes the "smoke" will make it look very dramatic.

I would strongly suggest leaving off the sprinkles, so there's no risk of one hitting somebody in the eye. In fact, you might not want to have somebody pop it by cutting it with a knife, because whoever does it is going to end up covered with nasty goop and their clothes will be ruined! That leaves you the question of how to pop it remotely. I have an idea for that, but it requires a BB gun or slingshot or something else that can definitely pierce a balloon that's covered with frosting.

You stick an unlit candle on top of the fake cake. (It might be good to tape it to the top of the balloon, before you put the frosting on.) At the party you say, "And now we're going to present an amazing trick! (The kid, his best friend, Dad, Mom, or whomever) is going to light the candle by shooting it!" But the shooter actually aims for the cake, not the candle. KABLOOEY, the balloon pops, frosting goes everywhere, no fingers are lost or eyes are put out, a safe and splendid time is guaranteed for all.

(Failing that, somebody may have to put on something smock-y, get a knife and "cut" the cake knowing they are about to get a faceful of cake. Just be sure you close your eyes first!)

Of course, then you have a real cake you bring out. After the laughs die down, those kids are going to want some real cake!

I would strongly advise against anything involving firecrackers. There are plenty of safe ways to explode the cake without involving gunpowder. (I am kind of an anti-firecracker scold, sorry.)
posted by Ursula Hitler at 2:22 AM on May 24, 2015 [1 favorite]

I think Ursula Hitler's got it.

I feel it necessary to tell you that your son is the coolest kid in the world .
posted by kinetic at 3:25 AM on May 24, 2015

Alternatively, there's an item called an "Amazing Happy Birthday Candle" available on Amazon from a few different sellers; kind of a combination of a sparkler, a music box playing the happy birthday song, and (depending on the version you buy) 8 or 16 candles. Flashy, noisy, and the cake is still edible afterwards, instead of splattered all over your walls.
posted by easily confused at 8:26 AM on May 24, 2015 [1 favorite]

Watch the first 38 sec of Propane Rifle. If you placed the cake on the cut off end of a largish bottle you might get what you are looking for. Bonus: With a long enough tube your son could give a countdown and pull the trigger.
posted by tinker at 4:34 PM on May 24, 2015

Something like the tube of a large potato gun loaded with a core of cake would shoot it many feet into the air (depending on the pressure you filled it with), you could build a real (edible, iced, flavourful) bundt cake and have the tube of the potato gun go up through the hole in the middle, so the outer cake would be for serving, and the central cake should also be edible - so it doesn't matter if some spatters down on the main cake, but would mainly be sacrificial. It'd be like a sort of compressed air cake mortar.
posted by The Monkey at 7:35 PM on May 24, 2015

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