Frosting (Beat light the whites of eggs)

This is an uncooked royal-style icing: raw egg white beaten with sugar and spread on a cooled cake, with no heat applied at any stage.

• Why it fails todayThe egg white is never brought to a safe temperature, and the finished icing is eaten as-is. Raw shell eggs carry a real risk of Salmonella, and sugar does not pasteurise them; the risk is highest for children, older people, pregnant women and anyone immunocompromised, who are also the likeliest eaters of cake frosting.
• Sugar is not a preservative hereOne cupful of confectioner's sugar to two whites gives a soft, damp icing that sits at room temperature for hours while the cake is served. That is a holding condition, not a hostile one. A current royal icing or buttercream recipe should be used instead.
• What the original expects of you"Beat till stiff enough, for half an hour or more" assumes beating by hand; the recipe names no implement. The long beating is what built structure in an icing with no cooked syrup and no cream of tartar.
• Confectioner's sugar of the periodWhat was sold as confectioner's sugar in the nineteenth century was not standardised, and generally lacked the cornstarch added to modern powdered sugar; a coarser or lumpier sugar may account for some of the beating time.
• CoverageTwo whites and a cup of sugar makes a modest quantity of soft icing, enough for the top of a small cake.