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My friends and I had this idea while drunk one night, to create a big batch of small cakes shaped like LEGO bricks and interlock them into a larger, round cake. Morning came, and we grew daunted by the task we had set, so promptly gave up. My question then, is this: were we right to give up, or is this actually a possibility?

My primary concern is that cake seems a fairly fragile material. The hollowing process for creating the bricks may spell an end for it right from the start, and even if it can survive that, how well will it be able to stack without collapsing on itself?

Secondary is a concern over the interlocking, how difficult would it be to allow modular construction and destruction? The original idea was only for a bigger cake, but if it works well that won't be where it stops.

Are there any techniques that could make this task more tractable? Cake recipes that might withstand the stresses better?

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Whatever you were drinking, either drink it a lot more, or stay away from it completely... I am not sure which... –  SAJ14SAJ Apr 22 '13 at 20:28
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4 Answers

up vote 3 down vote accepted

You never said what size the cake had to be, or how well it had to actually hold together.

If you make too large of a cake, it's not going to work -- cake is heavy enough that as you get larger, you need to add additional supports. Most multi-tier cakes have some sort of rods (plastic or wood) placed in them to help support the upper levels. If you make it too small, you won't have sufficiently sized knobs for it to actually be able to hold anything.

Most professional cakes are more dense than your home-baked cakes, to help get around this issue, and you can chill them to help firm them up before stacking. If you're going for a recipe from scratch, look for a pound cake recipe. If you're using a box mix, you can add in a packet of instant vanilla pudding mix and reduce the temperature by 25°F / 15°C but increase the time.

Size will be an issue as the larger that you get in a single cake, the weaker it's going to be; the bit of crust that you get from the pan is more significant the smaller the cake is. It'll also be stronger when the dimensions are all close (ie, more cube-like), as you don't have issues with things breaking off due to slenderness.

Your next issue is the connections. As we're not dealing with plastic, we can attempt to take advantage of two things -- friction, and compression. To get friction, we need the surface to be rough and fairly strong ... and this means that carving it down is right out, it'd have to be cast directly if it's going to have any strength. You'll likely have to play with the sizing of the holes vs. the knobs, but you'll want the knobs to be large enough that it's a press-fit, and takes a little effort to seat them (compressing the knob in the process), but not so much force is applied to the cake that it causes a failure at the wall around the hole. If it were me, I'd try to make the knob between 1/3 to 1/2 the length of the cake, and the knob stick up 1/4 of the depth.

And now you're wondering of course how both the top and bottom could be cast -- by making two molds, and gluing the top and bottom together using icing. Depending on the strength required, you might have to add some rods to pin it together ... but one vertically through the knob will only help you in compression and sheer, not tension. For that, you'd need three or more diagonally through the knob in a radial pattern. I'd personally avoid the supports, with the argument that it's no longer fully edible, and might not be a cake anymore. (and those who enter gingerbread cake competitions would instead just use something edible as the rod, like an un-bent candy cane).

So, to summarize:

  • You'll need two molds, one for the upper, one for the lower, bake, level, then join them together.
  • The knobby bits in theory should be 1/3 to 1/2 the length of the side, and about 1/4 of the total height
  • The knobby bits should be slightly wider than the hole they're fitting into.
  • Avoid slender pieces (ie, no 1x4 pieces; 1x1 or maybe 1x2)
  • Stiffen the cake with gelatin, refrigeration, and bake at a lower temp (but you need to cook it longer to get a bit of crust to form)

And now, for the reason it just won't work :

Depending on what you're willing to qualify as 'cake', this could be possible to make out of gingerbread (as used for cookies and houses, not cake), but you'd have to dry it so far that it'd not cut like a conventional cake. (make it from layers, then laminate them to make individual pieces, you might have to use hole saws after they're dried to get the proper sized knobs and holes, and then sand to get 'em perfect)

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I was thinking about either carving the edges, or casting edge pieces specifically. Good explanation of the stresses involved, and how to stiffen the cake for less fragility. –  Sconibulus Apr 23 '13 at 12:18
    
And as SAJ14SAJ has mentioned -- part of this is speculative ... but I also have a degree in civil engineering (although have never practiced it professionally) -- the inability for a cake to support tension is the same problem you have with concrete -- and have done a fair bit of cake decorating through the years. –  Joe Apr 23 '13 at 12:27
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You could certainly build a cake to look like it is made of Lego blocks.

However, I don't think that any cake is going to be strong enough to actually play with and move around, even if you could be precise enough to make the bumps fit the holes (or mortises fit the tenons or whatever the right terminology is for a Lego block).

Even the firmest strongest cake (probably a dense pound cake) will not stand up to that kind of treatment. Cake is not smooth like plastic, so you would need considerable clearance. The holes would have to be significantly larger than the bumps. Cake also has essentially no strength in tension (pulling it apart is easy), even though it can stand some compression (as demonstrated by the wedding cake industry—and even there, often there are dowels and cake circles in the construction to fortify it) The top cake would just rest on the bottom cake by gravity, not be joined.

You certainly would not find any cake that you can actually join together so that they could be picked up as a unit through the strength of the joint.

Then there is the issue of construction; you would either need to create custom molds, or somehow hollow out the holes, and join the bumps on. Neither of those are going to be very robust.

Now, for looks, just google "lego cake image"....

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As you always seem to complain about downvoting, and I so rarely do it -- my justification is argument from ignorance –  Joe Apr 23 '13 at 9:22
    
I stand by my answer. While you could certainly make such cakes that could be stacked once under gravity and compression, due to the minimal tensile strength of cake, the high friction of cake on cake (and worse friction of icing on cake if used in the construction), being able to played with or permitting "modular construction and destruction" as asked in the question is an extremely difficult goal. I certainly don't believe you could build anything that could be lifted by the top cake--that is be truly snapped together. It is more than a rigorous enough analysis for a drunken question. –  SAJ14SAJ Apr 23 '13 at 10:36
    
re-read the original question ... the ability to re-use the cake was a secondary concern ... and he never once said that you had to be able to lift the whole thing from a top-most cake. But any lego fan would know that if you build too large of a structure you can't necessarily lift it from a single piece. –  Joe Apr 23 '13 at 12:21
    
If you don't move them, its essentially cosmetic in any case. Which goes back to all of the google images. –  SAJ14SAJ Apr 23 '13 at 12:43
    
you can't lift a full cake from its top tier, either ... you have to support it from the bottom. This is why my first statement of my answer was that he hadn't fully specified what the requirements were. Everyone has their own opinion for what are the defining characteristics of an item are. If you want to be able to move it easily, you could use the gingerbread idea to make a base plate to construct everything on top of it. (but it might need to be set on top of a sheet of MDF or plywood for really large sizes) –  Joe Apr 23 '13 at 12:51
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Legos work because the material they are made from is both elastic and durable, and they are designed to take advantage of this - the "nubs" atop the brick can be forced into the cavity at the bottom of another with an audible snap. More, if you look in the bottom of the brick, you will see various structures built into the brick to reinforce the shape of the piece, and keep it under enough tension to keep the other brick plugged into it.

Cake has two problems -

1) it's not very elastic or rigid, being made of cake. 2) It cannot be engineered to retain its shape, as cake is by necessity has much thicker walls. 3) It will bake into an unpredictable shape, even in a mold - you will need to trim and carve out hollows for the nubs underneath.

You will be relying on the coarse friction to keep the pieces together, and... and... and... nevermind. I can see you really want to build a lego cake. Have at it.

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I think it could be done as my wife makes plain victoria-style sponge cake so light that you can barely feel you're holding it. As your question specified making lots of small cakes, I would suggest that rectangular blocks, about 2" x 1" x 1" (50mm x 25mm x 25mm) would be ideal. In volume they'd be about half the size of a cupcake. I know that you can get rectangular cake moulds. I wouldn't worry about the underside of the cakes too much, but I'd make an inlay to put in the bottom of the moulds to get the Lego shaped top. Once they're cooked, you could carve a small amount out of the bottom for the "nubs" to fit into. You won't get a "snap-fit", but I reckon that for your purposes you'd be happy just to have them look right, and let gravity hold them together. Off-topic, you've inspired me to try to make a set of Tetris cake moulds.

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