Jet Truck Cake

This cake was for my nephew, Sam’s, first birthday. It’s based on a real truck.

When I asked Sam’s big brother Nathan, who was, at the time, almost four years old, what kind of cake he thought that Sam would like for his birthday, he gave me very detailed specs:

  • Tractor-trailer – w/o trailer
  • Racing truck
  • Racing trucks are yellow.
  • Jet engines on the back
  • Flame powered engine
  • Flames come out of exhaust pipe
  • Flame powered fuel
  • Button to turn on flames
  • Nathan will show Sam how flames work
  • Flames come out of jet engine
  • Flame powered fuel tank on the side

When I showed my notes to my sister, Nathan and Sam’s mom, she immediately knew what truck he was thinking of. Evidently he had seen it in a video on youtube. A few google searches later, I had some great reference photos to work from.

Since the planned birthday party would be attended by numerous small children, I decided that having actual flames shoot out the back of the cake would be a bad idea, even if I could accomplish it in a food-safe way. Instead, I planned to make basically a miniature version of the flames on those plastic Halloween cauldrons where a light and a fan inside the cauldron make some waving fabric look like relatively convincing flames.

Ultimately, it didn’t work out nearly as well as I had hoped, for several reasons:

1)    Initially I had hoped that I would be able to substitute something edible for the fabric “flames” but I was unable to come up with any food item that was thin, dry, lightweight, and flexible enough to fit the bill. The closest I came was the skin of a bell pepper, but that was too brittle when dried.

2)    I bought white fabric, but then dyed it red and orange with food coloring, which stiffened it a bit more than was optimal so it didn’t move as fluidly as I wanted.

3)    Fans small enough to fit inside a 2” diameter gum paste rocket aren’t all that powerful. I bought a couple of different ones to try out. I thought the ones I decided on would work, but once I got them all the way hooked up with the fabric I found that they didn’t have enough punch to move strips of fabric more than a couple inches long.

4)    When I stuck the fabric to the gum paste rockets, I did it in such a way that the air only passed over one side of the fabric, not both. Unfortunately, I didn’t realize what a big error this was until it was too late to do anything to fix it.

5)    When I installed the fans and rockets on the cake, I didn’t leave enough room at the back of the rocket for air to get sucked into the fan. Again, I realized the error too late to correct.

So the flame effect wound up being mediocre at best, but otherwise I think I captured the essence of the jet truck pretty well.

For the base, I started with a trapezoid of plywood. I guess I though that a trapezoid would give it more of a sense of motion than a rectangle, but I’m not sure it really did much. I used grey run-in royal icing, with white and black food coloring sponged on to make it look like asphalt. On top of that I painted yellow lane markers with thinned royal icing and then yellow food coloring.

To raise the body of the truck up off the ground, I mounted a second, thinner piece of plywood, on top of some sections of 1” aluminum channel, positioned so that that channel would later be hidden behind the tires. I covered this piece of plywood with black fondant.

At this point I did all the wiring for the fans and the LEDs to light up the inside of the rockets. I got some nice big red buttons to turn them on and off because I thought that Nathan would enjoy that.

Next, I used gum paste, detailed with royal icing, to make the rockets, the grill, the spoiler, the hubcaps, the wheel wells, the fuel tanks, the bumpers, the reflectors, the license plates, and so on and so on. I used fondant for the tires and a few of the other bulkier trim pieces.

Shiny chrome truck bits gave me a chance to try out my new metallic edible airbrush colors. I was a bit skeptical, but they worked great. I was especially pleased with the job I did on the rockets.

For the cake itself I started with three 10” square cakes, carved into the two separate pieces of the cab, then crumb-coated with buttercream. Once covered with fondant, the corners were more rounded than I wanted, giving the truck a more puffy, cartoon-ish look than I would have liked. I’m reaching the conclusion that the only way to get nice, sharp mechanical corners is to pre-make gum paste pieces like I did for the Tardis cake.

My plan was to cover the front cab section first with blue fondant then with yellow fondant so that I could cut the yellow fondant away from the windows revealing the blue fondant beneath. (This is after I decided that my original plan to actually create an interior for the truck that could be seen through the windows was not feasible in the time I had available.) I have never personally tried this technique before, but I have seen them do it many times on Ace of Cakes, so I figured I ought to be able to do it easily. It probably would have worked just fine, except that I decided to wait to cut out the windows until after I airbrushed the orange and red stripes onto the cake.

Masking parts of the cake off and airbrushing is another technique I’ve seen on Ace of Cakes, but this was my first try at it. It worked relatively well, but next time I’ll be more careful with my masking, since I did have a few spots where the color bled under the paper.

By the time I was finished airbrushing, the top yellow layer of fondant had completely fused to bottom blue layer of fondant, so it was utterly impossible to remove one without removing the other. So I cut all the way through both layers for the windshield, the side windows, and the front grille, all the way down to the crumb-coat, and then stuck a new piece of blue fondant into the hole. To give it a window-like gloss, I painted a layer of piping gel onto the windows.

Assembling the rockets around the fans and the lights was a bit of a challenge, both because I kept getting confused about which side of what rocket each wire was supposed to go on and because I had underestimated the required length of a few wires and had to splice in some extra pieces.

Then it was just a matter of attaching tires, fuel tanks, trim, etc. and running a strip of ribbon around the edge of the base to hide the side of the plywood. I stuck the candle into one of the exhaust pipes.

I’m happy to say that Nathan was delighted with the cake, even though the flames were a little lame.

I tried putting edible glittering into the rockets so that it was blown out when the fans were turned on, but that wasn’t too dramatic either. Mostly I think Nathan just liked pushing the buttons.

Sam was pretty impressed with the cake, too, although he didn’t actually get any of it, because I foolishly used a chocolate cake recipe that involved almond extract and my sister didn’t want to give him nuts yet for fear of allergies, so we made a last minute emergency batch of cupcakes with a nut-free recipe. Sam was very much in favor of the cupcake. I think the only food I’ve ever seen him enjoy more was pumpkin pie. Nathan, on the other hand, was most entranced with eating the gum paste pieces. At one point in the party he ran past me, doing a little happy dance, singing, “I have an exhaust pipe!”