Not every food requires an ingredient label.

Certain foods, defined by "standards of identity," traditionally have been exempt. The contents of these foods were assumed to be familiar to the public when the 1938 Food, Drug and Cosmetic Act was passed. But what was familiar then and what is familiar now are entirely different matters. As a result, the "to label or not to label" question is has no clear answer.

The Food, Drug and Cosmetic Act enabled the Food and Drug Administration to prevent adulteration of food by setting certain legal criteria for labeling. The standards of identity, based on common recipes for common foods, establish mandatory ingredients for familiar products (such as oil, vinegar and eggs in mayonnaise) and allow optional added ingredients (such as salt, spice and lecithin in mayonnaise). The mandatory ingredients do not have to be mentioned on the label.

Peanut butter, for instance, must contain 90 percent peanuts. The FDA cannot require peanut butter makers to put "peanuts" on ingredient labels. But peanut butter may also contain salt, sugar, vegetable oil and specific additives identified by the FDA, and they must be identified on the label.

In the last 10 years or so, the FDA has systematically worked to require labeling of optional ingredients on all standardized products. As a result, says Taylor Quinn, FDA's associate director for compliance in the Bureau of Foods, most manufacturers list all ingredients voluntarily.

In addition, the FDA has suggested many times that Congress change the law so that people who make vanilla extract, for instance, have to list ethyl alcohol--a mandatory ingredient--on their ingredient labeling. So far, says Quinn, Congress hasn't followed through.