| I think that crumb wouldn't even be recognized as what it is because people don't watch it closely. They ust hate it when the feel it under their ellbows while they're watching tv.|
Anyway, you could take any primitive, cube, prism or something, then boolean-subtract a whole a lot of little spheres of random sizes. The spheres are the "holes" in the bread, they come from the sodacorbonate that reacts with the starch and build carbondioxide. Or something. Anyway, just subtract a lot of random spheres, a bit like emmenthaler cheese or a sponge.