When baking bread and other pastries, some recipes call for an egg wash, others for brushing the top with milk. Are they interchangeable?
April Finnegan, New York, NY
Nicole Rees replies: Brushing with an egg wash gives a different effect than using milk, so they are not interchangeable. Pastry chefs use an egg wash primarily for shine, though the egg yolk will contribute a golden color to the finished baked product. For a clear shine, an egg white alone can be used. Milk, on the other hand, is used to encourage browning. For example, scones and biscuits will be pale on top (even though the bottom side is brown) if not brushed with milk or cream before baking.
Dairy products contain both amino acids and certain types of sugars that react with one another in the high heat of the oven and undergo what is called the Maillard, or browning, reaction. This process creates the appetizing golden color we see, but more important, it develops the savory flavor of browned foods.