Acid

An acid produces the sour flavor found in various foods; the term also denotes a chemical intensity. If hydrogen is produced when a substance is submerged in a water solution, that substance is acid to some degree. The degree of acidity is expressed by the hydrogen concentration, commonly known as pH. The pH scale goes from 0 to 14, with 0 being very acid and 14 being very alkaline (the opposite of acid). At the center of the scale, with a reading of 7, is pure water, which is neutral. The word acid comes from the Latin acidus, meaning “sour.” Some naturally occurring acids are found in vinegar (acetic acid), wine (tartaric acid), lemon juice (citric acid), sour milk (lactic acid), and apples (malic acid). Acids can be used as tenderizers because they break down connective tissue and cell walls. They are also used to give foods a tart taste and, in wine, they make the flavor more interesting and complex. The citric acid in lemon juice is used to prevent cut fruit from oxidizing (see Acidulated water), and acids help to coagulate proteins, which is why lemon juice or vinegar is added to the water used when poaching eggs. A small amount of acid such as lemon juice, tartaric acid, or cream of tartar is used in making meringue in order to lower the pH level in the albumen (the egg white). Citric acid is also added to both the dough and the butter block in the production of puff pastry to make the dough more pliable.