When measuring acidity in foods and beverages there are two common units of measurement: titratable acidity and pH. There is no direct relationship between pH and titratable acidity, therefore, both must be measured experimentally. Titratable acidity (TA), also referred to as total acidity, measures the total acid content in a food or beverage system and is determined by titration of the acids in the food system with a standard base. BASIC PROTOCOL POTENTIOMETRIC AND COLORIMETRIC ACIDITY TITRATIONS The choice of titration protocol to determine the TA of a sample is dependent primarily on the color of the sample. The colorimetric titration uses phenolphthalein indicator solution to determine the endpoint of the titration. Phenolphthalein indicator solution turns from colorless to pink upon reaching the endpoint; therefore, if the color of the sample interferes with this color change, the potentiometric titration is the best method. However, when using colorimetric titration, it is also common to titrate to an endpoint of pH 8.2, the endpoint of the phenolphthalein solution. Materials Sample Deionized, distilled water (ddH 2 O) 0.1 N sodium hydroxide solution, normalized (see recipe) 1% phenolphthalein indicator solution pH meter (Corning, Orion) pH electrode 250-ml beakers (potentiometric titration) 250-ml Erlenmeyer flasks (colorimetric titration) Small magnetic stir bars Blender (optional; if the sample needs to be macerated) Magnetic stir plate 50-ml buret Buret clamp Clamp support Stopcock Small glass funnel Contributed by Jane E. Friedrich
