If you are a maker of pastry you probably have, at one point of another, lovingly brushed some buttery dough with a beaten egg, or some portion of an egg, never stopping to wonder why. (Or maybe you did wonder why. I’m not in your brain box.)
For many years, I these followed such instructions blindly, never pausing to consider the differences between an egg white wash, a yolk wash, or a whole egg wash. Chemically-speaking, the differences between a white and a yolk are vast, and they have very different effects on pie crusts and other pastries. Here you can see how these various washes affect both the color and the finish of flakey, delicious goods.
No Wash
Somewhat paradoxically, the pastry without a wash is the cleanest. It’s also the most matte, and will brown and crisp up without any discernible shine.
White-Only Wash
When whisked until frothy, this wash provides quite a bit of shine and a nice, golden color, while browning more slowly than a wash that contains yolk.
Yolk-Only Wash
A yolk-only wash with give you the darkest, richest color and the shiniest finish in the shortest amount of time. Due to its thicker viscosity, it’s much more likely to hold brush strokes, or any other pattern you happen to make in it.
Whole-Egg Wash
Predictably, this wash is somewhere in between a white wash and a yolk wash. This wash may look very similar to the white-only wash, but it got to this golden brown point much more quickly. The more thoroughly you beat the egg, the more even the wash will be, so whisk until frothy for the best results.
Also, keep in mind that you aren’t limited to one wash per pie, and can alternate them to create patterns or give a design depth. Alternate white and yolk washes to give a lattice some dimension, or paint cut outs with yolk while leaving the crust plain. Want to claim a pie as totally yours? Paint your name in a bold yolk wash for all to see.