Adulteration of food is relatively modern. Home-grown, home-cooked food may lack purity through ignorance or neglect, but only industry-produced, factory-prepared, shop-served food is ever adulterated. An effort is always made to provide pure food when the purpose is human nutrition.

Food laws purpose to protect humanity against abuse of food for financial advantage. What science finds harmful, law forbids; what is in doubt, law usually permits. But there is increasing scientific direction of all that affects the food of humanity; also increasing law control.

Substances known to be dangerous to life, if added to food for any purpose, would be adulterants. Such additions are, however, not usual. Substances not themselves foods are still used, which are introduced to improve appearance, such as chemicals to keep canned peas or beans green or to permit prolonged keeping of food for gain. Law requires that the presence of most of these be stated on food-labels, such as talcum coating rice. Better health results from not eating even supposedly harmless substances if they are not human foods.

Lessening nutritive value of foods, as watering milk, is adulteration; adding to weight would also be. This is now more rare. Coloring or thickening to pretend a quality not possessed by the food is food-adulteration, too. Such is thickening cream with gelatin or producing seeming freshness in stale food by chemicals, as change of color in meat, or preventing by chemicals natural changes in food, as the souring of milk. Substitutions in commercially prepared foods as chicory in ground coffee, food laws prohibit; also concealed substitution of a cheaper food-ingredient of equivalent use, even if itself not unwholesome, for a more expensive, such as glucose for sugar in candies, oleomargarine for butter, cottonseed-oil for olive-oil.