Egg white, or albumen, is the clear, viscous fluid that surrounds the yolk — nearly pure protein and water, almost fat-free and barely scented. On its own it is bland and watery, but it is a workhorse of the kitchen: whisked, it unfolds into a glossy foam that carries meringue, soufflé and angel cake; heated, it sets into a firm, springy white; and it clarifies stocks, binds coatings and lightens batters. It is also the part of the egg that carries most of its allergenic proteins.