An acid is a substance capable of turning blue litmus paper red and of forming hydrogen ions when dissolved in water. An acid aqueous solution is one with a pH less than 7 (see pH). Acidulants are acids that make a substance more acid and function as flavoring additive to acidify taste, to blend unrelated flavoring characteristics, and to mask any undesirable aftertaste. Acidulants are also used as preservatives to prevent germ and spore growths that spoil foods. Acidulants controlÂ the acid-alkali (pH) balance and are used in meat curing to enhance color and flavor and as a preservative. Among the most common acids added to foods are acetic, propionic, and sorbic. Winter, Ruth (2009-04-04). A Consumer's Dictionary of Food Additives, 7th Edition: Descriptions in Plain English of More Than 12,000 Ingredients Both Harmful and Desirable Found in Foods (Kindle Locations 1405-1408). Crown Publishing Group. Kindle Edition.