To cook out means to cook a food completely, particularly a sauce, so that no trace of raw flavour remains. A sauce containing flour must be simmered long enough to lose its pasty rawness; tomato sauces need time for their sharp acidity to mellow; alcohol in a dish should cook until only its flavour, not its harshness, remains. The instruction appears in recipes where undercooking leaves an identifiable fault. Judging the point takes tasting rather than timing alone. It is a reminder that cooking is transformation, and that some ingredients only become themselves after sustained heat.