The forming of egg white plays an important role in many foods because it makes the products light in texture and contribute to leavening. Egg white foam is a collide consisting of bubbles of air surrounded by albumin that has undergone some denaturation on the liquid air surfaces. This denaturation which is due to the drying and stretching of the albumin during beating makes some of the albumin insoluble thus stiffening and stabilizing the foam. During denaturation the protein molecules unfold and their polypeptide chains lie with their long axis parallel to the surface. Over beating incorporates too much air, stretching the albumin so that it becomes thin and less elastic. Elasticity is needed especially in foams that have to be baked so that before the albumin is coagulated by the heat of the oven, the incorporated air can expand without breaking the cell wall.
The ease with which the egg white can be whipped to a fine foam with small air cells is attribute to the presence of ovomucin, ovoglobulin and conalbumin. Duck eggs are deficient in globulin do not foam.
Table: shows the description and uses of egg white foams.
Table: Characteristics and uses of egg white foams
Stage
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Description
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Uses
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Slightly beaten
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Frothy, slightly foamy, large air bubbles, transparent, flows easily
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Clarifying, coating, emulsifying and thickening.
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Stiff foam
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Frothy quality disappearing, air cells smaller, whiter, flows, very shiny, glossy and moist in appearance, if left to stand liquid separates out readily, when beater is withdrawn white follows forming rounded peaks.
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Meringues
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Stiff
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Air cells small and white, glossy, smooth and white in appearance.
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Cakes, omelettes, ice-creams, soufflés.
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Dry
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Very white but dull. Small flakes or curds beginning to show. Rigid and almost brittle. If left to stand liquid separates at the bottom slowly.
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Shirred egg.
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