When I worked in pastry and we cycled through endless trays of egg-washed burger buns, it felt miraculous every time we pulled out the perfectly golden, shiny rolls out of the oven. Occasionally we missed one in the rush to bake and its pale dullness stood out, the ugly duckling among its beautiful siblings. It never became a swan, but we did get to eat it—almost as good.
The magic of egg wash, the secret behind shiny burger buns and this beautiful pizza braid, relies on the Maillard reaction, the same chemical process that gives us the browning on toasted bread and seared meat. For that characteristic color and flavor, the reaction requires protein, sugar, and high heat (around 300 degrees F): all present in the original bread dough. And yes, you’ll get some Maillard browning on regular baked bread for passable golden color, but egg wash takes us from the minor league to the majors. The extra layer of protein on the outside of the dough gives you more browning for deeper color and a delicious toasty flavor.
Egg wash also takes bread from dull to high gloss, thanks to another component of the egg wash: fat. The fat in the yolk creates a shiny finish, similar to the pretty glaze of brushing butter on top of scones.
So protein makes bread brown and fat makes it shiny. Armed with this knowledge, you can create a wide variety of finishes (it’s like a manicure, but more delicious). Want dark color but no gloss? Use just egg white to take the fat out of the equation. Want even more shine? Bump up the fat by beating your egg wash with some heavy cream. Any way you do, egg wash makes beautiful things happen.