Other meanings of Egg white
Food biology
Egg white is albumen, the protective protein-rich fluid surrounding an egg yolk. It supplies water and proteins to a developing embryo, cushions the yolk, and helps defend the egg against microbes. In cooking, its proteins create foams and set into an opaque gel when heated.
Egg white is a multilayered fluid rather than a chemically uniform liquid. It surrounds the yolk inside the shell and is organized into thin and thick albumen, with the thickest regions connected to the chalazae that help hold the yolk near the center.1 Most of its mass is water; proteins account for roughly a tenth, while fat and carbohydrate are present only in small amounts. A large raw chicken egg white supplies about 17 kilocalories and 3.6 grams of protein, with negligible fat.2
Ovalbumin is the dominant protein, accompanied by ovotransferrin, ovomucoid, ovomucin, lysozyme, and other minor proteins. Their differing structures give albumen its unusual combination of viscosity, foaming ability, antimicrobial activity, and heat sensitivity.
Egg white protects the yolk and developing embryo through physical separation and several biochemical defenses. Its viscosity slows movement of microorganisms, while proteins such as lysozyme can damage bacterial cell walls and ovotransferrin binds iron, making that nutrient less available to microbes. Ovomucoid also inhibits trypsin, an enzyme involved in protein digestion.1
The white is produced in the hen's oviduct and deposited around the yolk in successive layers as the egg passes through it. The chalazae are twisted strands of dense albumen, not embryonic structures; they anchor the yolk while allowing it to rotate. In a fertilized egg, albumen therefore serves as both a protective medium and a reserve of water and amino acids, although the embryo also receives nutrients from the yolk.
Egg white becomes useful in cooking because its proteins unfold and link together when disturbed or heated. Whisking incorporates air, and the resulting foam is stabilized largely by proteins at the air–water interface; sugar, acid, and fat alter the foam's stability. Even a small amount of yolk can weaken a meringue because yolk lipids interfere with that interface.
Heating causes coagulation, turning translucent albumen white and firm. Gentle heat produces a tender gel, whereas excessive heat drives out water and creates a rubbery texture. Egg white is a high-quality protein source but contains little of the yolk's fat-soluble vitamins and minerals. Raw or lightly cooked white can carry Salmonella; the U.S. Food and Drug Administration advises cooking eggs until both white and yolk are firm, with special care for vulnerable people.
Egg white has applications beyond ordinary cooking because its proteins can form films, gels, emulsions, and foams. Ovalbumin is also a widely used laboratory protein and a major reference allergen in studies of egg allergy. Ovomucoid is particularly resistant to heat and digestion, which helps explain why some people react to cooked egg as well as raw egg.3
Freshness changes albumen's physical behavior: carbon dioxide gradually escapes through shell pores, raising the white's pH and making it thinner. This is why older eggs spread more readily in a pan, although they may still be safe when properly refrigerated and cooked. Commercial pasteurization can reduce pathogen risk while retaining much of the white's functionality, but processing conditions must be controlled because heat can prematurely denature its proteins.4
Nutrient values vary with egg size and preparation; the figures given are approximate values for one large raw chicken egg white.
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