Food is a perishable product consisting of proteins, carbohydrates, fats, vitamins, minerals, water, and fibers. It is used by an organism in sustaining growth, repairing tissues, maintaining vital processes, and furnishing energy. Great pleasure is derived from the proper preparation of food and from its consumption. Food is altered favorably or unfavorably by microorganisms, enzymes, insects, and environmental changes. Microbes help produce sauerkraut, bread, and cheese; ripen olives; and ferment milk. The action of the yeast
produces carbon dioxide in bread, making it porous and causing it to rise. The starches and proteins in bread are split by the action of the yeast, becoming more digestible, and characteristic flavors and aromas are produced. However, if certain spore-forming bacilli, principally
, are introduced with the flour or yeast, discoloration and unpleasant odor results and the bread becomes unappetizing.