Since there is protein in both the yolk and the white, any whole egg or yolk will make the crust both shiny and brown. The white, on the other hand, will only promote browning without contributing any significant gloss to the crust.
What does egg yolk do to pastry?
Egg yolks and water also affect pastry. Egg yolks contain fat and act as an extra shortening agent but are used more to add colour and richness to the pastry. When you're adding water to pastry, be careful to add only enough to bring the mixture from a crumbly dough to one that can be kneaded and rolled easily.
What does egg yolk vs egg white do in baking?
Eggs yolks makes richer and softer baked goods, while egg whites give you a lighter and airier product. Most recipes call for a traditional large egg in baking. However, you can change the egg size to still get a rich final product, but reduce or increase moisture.
What happens if you use egg whites instead of yolk?
Egg whites are mostly proteins whereas an egg yolk is mostly fat, with some protein in it. The proteins in the egg white will cook and crisp up on the crust of the pastry. This will happen when you use egg yolks too, but the fat in the egg yolk cooks and frys the top crust, too.
Is egg wash for pastry just yolk?
And although the go-to egg wash is a mix of milk and whole egg, there are actually many different options when it comes to finishing your dough. Using the classic egg wash creates that familiar deep golden color, but you can also use just yolks for a darker, richer hue, or just milk for a matte, flakier look.

Below are two helpful articles on a similar topic 👇
Can you use egg yolks for tarts?Why is egg yolk used in shortcrust pastry?