Food products have rarely been used simply as taken from nature. Fresh vegetables, fruits, and milk are the only common foods now so used; even these are also eaten in many prepared forms. Canned foods are usually cooked and sealed. Sometimes they have, however, simply had the air excluded, as blueberries sealed in water, for use at sea, where they are taken to prevent disease caused by lack of food-salts.

Manufactured foods are not all cooked or canned. Some are only milled, as are most grains that are used as flours or meals. Grains must be in wholesome condition themselves, be ground under sanitary conditions, and kept clean and dry, to produce health-giving foods.

Originally only such foods were sold manufactured as would not otherwise be edible. Sugar and molasses have so long been used as manufactured foods that they are commonly accepted as natural in this state and the processes used to produce them are generally unfamiliar. Butter and cheese, though once home-produced, are now usually bought without thought as to their derivation. Jams and jellies from fruits, and soups from meats and vegetables, appear now as manufactured products for sale, but these are still also often home-made.

Foods of concealed composition are, as noted, beginning to appear. These must satisfy law standards for food. That a substance has the composition and characteristics that serve a given food-purpose does not essentially make it an acceptable article of diet. Oils made from food-refuse and called "salad" oil make little appeal to those that know their origin. Even cottonseed-oil needs to be known and sold as itself rather than as "salad" oil charged for as olive-oil.

Use food of which the composition can be entirely known and the process of its manufacture fully seen.