March 29, 2009

Dinosaur Graveyard Cake

Pastry arts for a good cause - this cake was raffled off at a fundraiser for my nephew's preschool.

Watch the train on YouTube
...and more
...and more

My nephew's pre-school was having a fundraiser. My challenge - make a cake for the raffle that fulfilled all of the following conditions:

The cake should be:

  1. Small enough that people wouldn't be intimidated by the prospect of eating it.
  2. Sturdy enough that there would be minimal possibility of breakage when the winner transported it home.
  3. Enough like a normal cake in appearance that people would recognize it as such when walking by the raffle table.
  4. Appealing enough to the average two-to-four-year-old that he or she could be counted upon to pester his or her parents into purchasing raffle tickets for it.
  5. Appealing enough to the average parent of a two-to-four-year-old that he or she would be willing, with some childish prompting, to spend a few bucks for a raffle ticket for a good cause.
  6. Appealing enough to me that I wouldn't get bored making it.

Collectively, these represent waaaay more constraints than I have ever had placed on one of my cakes before. Prior to this, my biggest restriction was when Barbara May and I made a cake for our friends' wedding and they said that, ideally, it probably shouldn't bleed, explode, or catch fire.

So I had a bit of a challenge developing an initial concept, but ultimately I came up with a solution that I think fulfilled all the requirements. Viewed from one angle it would appear to be an ordinary 12" round cake, covered with white fondant, delicately decorated with cornelli lace, so as to appeal to people who like their cake to look like cake. From the other side, however, the fondant would be cut away to reveal a subterranean tunnel with a train going around and around, so as to appeal to the toddler set. The train would be pursued by a ravenous dinosaur, so as to appeal to me.

I think I can best explain the process of construction by breaking it up into its component elements.

The train:
The first thing I needed was a way to make the train go. I figured the easiest thing to do would be to get some kind of battery operated car toy and build my train around it, so I went to Toys R Us. Mind you, I detest Toys R Us, for various reasons that I needn't go into here, but I was in a hurry and it was my best option for a quick solution. The toy I selected was a battery operated Thomas the Tank Engine, which turned out to be delightfully easy to decapitate, leaving me essentially with a AA battery on wheels.

In keeping with the subterranean / archeological theme of the cake, I found a photo of an old-timey mining cart to work from. First I encased the body of the train in a box made of flat gum paste pieces, with semicircles cut out to accommodate the wheels, then I added additional gum paste wooden slats. I used one of the semicircular cut off pieces from the wheels to cover the little magnetic hookup that toy train cars have on the back. I also made a cow catcher for the front. Because of all those cows that archaeologists encounter in underground caves.

I wanted to cover the wheels (which were bright green) with gum paste to make them more rustic and less plastic looking, but every time I tried, the wheels came out too big for the track (more on that later) so I wound up just painting the green wheels with black food coloring.

To get some human interest into my tableau, I wanted to put a little gum paste archaeologist in the train car. After all, no self-respecting dinosaur would be chasing an empty train car - a T-Rex in particular would need the prospect of juicy meat to get him moving. I tried to make my archaeologist look really terrified, with a gaping mouth and wide, staring eyes, looking over his shoulder at his dreadful pursuer. I also couldn't resist making him a little Indiana-Jones-style hat and a pickaxe. The train had a big button on top to start and stop it. At first, my plan was to put my little man directly on top of that button so that you had to push on his head to make the train go, but then I realized that was just too risky to be worth it - who wants to see a man with a smooshed head being chased by a dinosaur? So I moved him to right in front of the button and left the button alone. I'm glad I did because by the time I was done some crumbs or something must have fallen into the mechanism because the button got a bit tempermental.

I then put a coat of paint on everything, using paste food colors thinned with vodka. It has recently been pointed out to me that using vodka to paint things intended for children might not be 100% kosher, which had never occurred to me. I choose to assume that the majority of the alcohol evaporates away and that what's left is so minimal as to make no difference. Certainly my nephew has shown no ill effects from the last three birthday cakes that I've made for him.

With my base coat in place, I was ready to add fine details. I made some royal icing chains and rivets. I also added some royal icing dinosaur bones around my archaeologist, and threw in some oreo cookie crumb dirt for good measure. I used some more vodka (Woo hoo! Par-ty!) with bronze luster dust to make the chains look metallic.

The track:
Now I had an operational train, but a train doesn't do anyone any good unless it goes where you want it to go. So I needed a track. It took me five or six cardboard mockups before I got one where the tracks were the right width and the right distance apart and correctly positioned within the circle of the cake. Once I had a functional mockup that worked with my little toy train, I covered a foamcore circle with a 1/4" thick layer of white fondant and used my mockup as a template to carve the fondant away to create the two concentric circles of the track. With the fondant cut away, I needed to do something to cover the foam core revealed underneath. After a few experiments, I settled on painting the revealed foam core base red (which frankly would have been a lot easier to do had it occurred to me to paint it red before I covered it with fondant). Because I didn't do the world's best job of this, I dusted the track with a lot of brown and black powdered food coloring and silver luster dust to try to conceal my mistakes.

The dinosaur:
A little train by itself might be interesting enough for pre-schoolers, but I have loftier aspirations. To keep my interest, the cake needed a monster. And it had to be Big! Fierce! Mean! Prehistoric! RAAAWR! I settled on T-Rex.

Step 1 - find internet photos. Of course, the internet crazies have conflicting opinions on what T-Rex looked like, so I just picked the skin texture and color scheme that seemed the most appealing to me.

I made two gum paste bodies, because I wasn't sure quite what size I wanted. I wound up using the bigger one. By letting the gum paste dry for a few minutes, so that it developed a bit of a dry shell, and then bending the body a little I was able to create a delightful wrinkly skin texture.

In order for the dinosaur to chase the train, it of course needed to be on wheels. My first idea was to use the wheels from a tiny little toy skateboard. This didn't work at all. For one thing, toy skateboard wheels turn out to be very flimsy and not very well aligned. I know this is a shock, considering that I bought it for $3.95 at Target. For another thing, toy skateboard wheels are extremely small, on the order of 1/8" in diameter. Since my layer of fondant between the two track circles was on the order of 1/4" thick, I clearly had a problem. I tried to salvage my skateboard wheel solution by cutting larger plastic circles and gluing them to the existing skateboard wheels. Then I realized that this was a stupid idea and I should just make the wheels from scratch.

I cut two new sets of plastic wheels, larger for the front, smaller for the back and put hot glue rims on them so as to give them the requisite traction. For the axles I used brass tubing, encased in slightly larger diameter brass tubing to allow it to rotate freely. I attached these to the body of the dinosaur by using royal icing and by cramming brass tubing up into the body.

I tried to mask the wheels a little when I added the gum paste legs, but since I was simultaneously trying to position the legs as if T-Rex was in a full-out run, and since I was trying to conceal four wheels with two legs, I wasn't very successful. I chose a nice muted ochre and brown color scheme, with some purple and green details, again using vodka and paste food colors for paint. Once that dried, I used royal icing to make little teeth and claws. I of course couldn't resist adding a bit of food coloring blood to the tips.

The hookup:
I now had a train on wheels and a dinosaur on wheels but in order to make the dinosaur chase the train I needed to connect the dinosaur to the train. I cut and bent a piece of brass tubing into the correct curve. Gluing it to the dinosaur was easy. Gluing it to the train was exceedingly difficult. First I tried hot glue. Then I tried Superglue. Then I tried hobby cement. Then I tried epoxy. As it turns out, for some inexplicable reason, none of these things stick to the underbody of Thomas the Tank Engine, even after he's been roughed up with a flat file. Eventually I resorted to the king of household glues - Gorilla Glue. Because Gorilla Glue expands as it dries, I was terrified that it would push everything completely out of alignment, but it actually worked.

The tunnel:
With my train and dinosaur set, I needed a tunnel for them to run through. My original plan was to create a nice rocky texture by making a mold in the shape I wanted the tunnel to be, lining it with plastic produce bags (because they release easily from chocolate), filling it with crushed ice, and then pouring tempered chocolate over it. In my imagination, this technique created a beautiful organic texture. In reality, it created absolutely nothing of value because the chocolate set up before it got beyond the first layer of ice. I went to plan B.

Plan B involved making two concentric tubes of chocolate with holes in them to form the inner and outer walls of the tunnel. One would be 6" in diameter, to fit around the 6" round cake that would be in the middle of my creation. The other would be 12" in diameter, leaving a 3" tunnel for the train to pass through.

At first I envisioned creating these tubes by spreading chocolate over bubble wrap (which also releases easily from chocolate), cutting it into appropriate rectangles, and then wrapping the rectangles around cake tins of the appropriate diameter, all while the chocolate was set up enough to cut accurately but malleable enough to wrap around the cylinder. This didn't work either. By the time the chocolate set up enough to cut it was too firm to wrap, so it just cracked when I tried to bend it into the right curve. I was also having problems getting my chocolate in good temper, so it wasn't setting as firmly as I would have liked. Normally I would blame problems like this on my own relatively limited experience working with chocolate. In this case though I'm more inclined to blame the problem on the chocolate itself because, at the same time as I was making this cake, I was also making chocolates to raffle off at the event, and I was having spectacular success tempering chocolate bars that had been sitting in our cabinets for so long that they were essentially just big slabs of chalky blooms. For the cake, though, I was using a new bag of chocolate medallions from my local cake supply store and I couldn't get them in temper to save my life. So I choose to blame the chocolate.

My third plan was to wrap the 6" and 12" cake pans in tin foil and them pipe tempered chocolate onto them in an abstract pattern. Due to my issues with getting my chocolate in temper I was concerned with the stability of the structure and I thought that I might get it to be sturdier and set up faster by mixing in a little corn syrup. This is a technique that I used to good effect when I made the shrunken head truffles, but in this application it just seemed to make the chocolate more brittle. So the technique that I finally ended up with was putting the tin foil wrapped cake tins in the freezer and piping the (sort of) tempered chocolate onto the cold foil in an abstract pattern with lots of open space. This helped the chocolate to firm up quickly when it touched the cold foil so that it wouldn't drip down the sides of the cake pan.

Third time's a charm. This time my plan more or less worked, although I still wasn't happy with the temper of my chocolate and my finished pieces broke in a few places when I unmolded them from the tin foil. But I figured it was nothing I couldn't repair when I put it in place around the cake.

The cake:
The cake itself is actually the most boring part of this story. All I needed was a 6" round cake. I tried a new recipe for chocolate cake, but when I went to torte it I realized that it wasn't baked all the way through, so I had to make an emergency backup cake. Since I didn't have any more cocoa powder I went with a white cake, which turned out fine. I torted and filled that one with buttercream icing. My sister took the incompletely baked cake, carved a hole out of the center to remove the uncooked part, put some ice cream in the middle, and took it to a friend's birthday party so it wasn't a total loss.

The facade:
To make my 6" cake surrounded by chocolate cylinders look like a 12" cake with a chocolate tunnel inside, I premade two pieces of white fondant. One was a simple 12" circle to cover the top of the cake and tunnel. The other piece was to go part way around the perimeter of the cake, but it also had to appear to be cut away so as to reveal the tunnel inside. I rolled out a piece of fondant, then cut it into a sort of ragged trapezoid. I used a ball tool to thin out the rough edges then draped the whole piece over the side of a 12" cake pan to get the right curve. To make sure that these pieces were dry enough to maintain their rigidity I made them a week in advance.

Putting it all together:
With all my components pre-made it was a simple matter to place my 6" round cake in the center of my train track and piece together my chocolate tunnel around it. For some reason my 6" round chocolate cylinder was bigger than I needed it to be, but the fact that it was poorly tempered meant that it was easy to cut a slice off to adjust.

Chocolate tunnel in place, I stuck my fondant circle on top and my curved fondant piece around the edge with some royal icing. I was a bit concerned about the top fondant circle drooping, as a large section of it was unsupported. My concerns were not wholly unfounded, as close examination of the finished cake does uncover some definite unintended curvature to the top of the cake, but as it didn't seem to pose a risk of structural cake failure I didn't let myself get unduly concerned.

In order to integrate the dinosaur with the cake, I incorporated subtle dinosaur skeletons into the cornelli lace that I piped onto the fondant. I used a #2 tip because I was too lazy to use a #1 tip. I also put a couple of dinosaur skeletons onto the inner wall of the chocolate tunnel.

When we set the cake up at the fundraiser, we tried to position it such that children would be able to see it easily, but not grab the train. For the most part, we succeeded. Only at one point during the party did I have to shoo away a toddler who was trying to snatch the dinosaur. The cake was ultimately won in the raffle by one of the kids from my nephew's preschool. I hope that he and his family enjoyed it.

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