Reader Daniel asks:
I was wondering if you might have an insight into a question I have been trying to answer for quite some time. In some traditional cake recipes from central Europe (usually cakes that involve ground nuts as well, like a Linzer), the dough calls for the addition of hard-boild egg yolks, passed through a sieve. I always wondered what this is supposed to do to the consistency of the cake vs. using raw yolk, and what may have prompted the bakers to use yolks in such an unusual way. Do you happen to know anything about that?
Great question, Daniel! The answer is that hard boiled egg yolks are a tenderizer. Consider that for the most part wheat flour is the “bulk” — the building material — of a cake. There’s just one complicating factor: it contains gluten. That gluten is important to some degree. The network of intertwined molecules helps trap the gas and steam that allows the cake to rise.
Too much, however, and the cake gets tough. This is where the hard boiled egg yolk comes in. Think of it as “bulk” that comes with no other attachments. Literally. Added to a batter or dough the cooked bits (which are actually huge in the context of a cake structure) interrupt the gluten network. Not so much that it doesn’t function, but enough that it’s more tender than it would otherwise be (ground nuts do the same job, but if you want a lighter, fluffier texture, cooked yolk is a better solution).
An uncooked yolks added to the batter wouldn’t work as well. The liquid water and fats would just disperse into the mixture. Yes they’d add moisture and a little tenderness, but not nearly as much as the cooked yolk. Also the cooked yolk adds a pleasing yellow hue. I like to add it to biscuits and pastry crusts as well. Hope this helps!