Acid. The grams of total acidity, calculated as anhydrous citric acid, per 100 grams of juice or citrus product. Total acidity is determined by titration with standard sodium hydroxide solution, using phenolphthalein as indicator.
7 CFR § 93.2
Words used in the regulations in this subpart in the singular form will import the plural, and vice versa, as the case may demand. As used throughout the regulations in this subpart, unless the context requires otherwise, the following terms will be construed to mean: