The Science Behind the Myths

"It is not enough to know the principles, one needs to know how to manipulate"
~Dictionaire de Trevoux, in the first edition of Chemical Manipulation (1827)

For me, there is no baking without science. I cannot imagine being able to bake efficiently without understanding why I am doing these things. Obviously, plenty of the worlds best pastry chefs have minimal knowledge of the precise science of egg protein interactions in creme anglaise; the tempering eggs method that results in a perfectly smooth cream could have been discovered through trial and error, but if you just know the basis of the chemical reactions, it becomes much more simple.

Today in class we finished with a demo on Austrian Dumplings, the base of which is similar to pate a choux. As the chef placed the dumplings in boiling water he asked, and how do we know when they're done? Of course, the generally agreed upon answer was "when they float to the surface." Not true!!
Some background: pate a choux (in this case dumplings) and egg based pastries (such as quiche) puff up due to mechanical leavening. Eggs contain a lot of water (90% in whites, and 50% in yolks), when heated this water turns to steam and is trapped under the coagulated outer layer and pushes it up. The starch contained in the flour is insoluble when cold, but in hot water, it absorbs water (aka swelling). The density of starch is greater than water (why it falls to the bottom), and while throughout cooking the density of the dumpling (or gnocchi, or what have you) decreases, it never becomes lighter than water. So why does it rise? Water vapor forms bubbles that cling to the irregular surface and cause it to rise (take a cooked gnocchi, roll it around on a cutting board to "pop" the bubbles and it will again sink-even though it is fully cooked). Buoyancy occurs regardless of interior temperature, watch a small gnocchi and large both rise around the same time with drastically different temperatures. So, if you make your dumplings at a precise size, in a precise water temperature, these actions may occur at the same time (rising and fully cooked), but if not they may pop up well before they are in fact done. Further, the answer to why they come to the surface in the first place was "steam," in reference to the same steam that causes the dumplings to puff up. Again, not true.
I never know what to do in these situations! So, to be safe I don't say a thing. I'm not about to be known as "that girl" who thinks she knows everything, or insists on correcting less then pertinent information. But, still it bothers me. So to make myself feel a bit better about the mass mis-information relayed in class today, I'm writing up the truth in the hope that for perhaps a few people, this old myth can be dispelled.