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Many recipes for old-world cakes, call for whisking egg yolks with sugar until a pale yellow foam forms. As the mixture is whisked, sugar dissolves in moisture present in the yolks, forming a syrup that traps air bubbles, which produce a light, spongelike texture in the cake. This is called ribboning because you can tell the foam is stable when it streams off the whisk in a long, unbroken ribbon.