Egg wash is a mixture of beaten egg and water or milk, that is brushed onto the surface of baked goods before baking which gives the pastry a glossy finish and helps it to brown evenly during baking. When making a pie, egg wash is used to give the crust a shiny, golden-brown finish. The protein in the egg helps to set the crust, giving it a slightly crisp texture, while the liquid helps to brown the crust and add flavor. The egg wash also helps to seal the edges of the pie crust, preventing the filling from leaking out during baking. To apply an egg wash to a pie, use a pastry brush to lightly coat the top and edges of the crust with the egg mixture. Be sure to avoid applying too much egg wash, as this can cause the crust to become soggy or burnt.