The Titratable acidity test is employed to ascertain if milk or milk products are of high acidity. The acidity of milk is not the true measure of lactic acid present but in practice, gives a good indication of the quality of milk. The Titratable acidity really measures the buffering capacity of milk and milk products and not true acidity. Fresh milk acts as a complex buffer because of its content of carbon dioxide, proteins, phosphate, citrate and a number of minor constituents. Bacterial action introduces lactic and other organic acids as additional buffers. Titration of milk and its product against standard alkali such as 0.1 normal sodium hydroxide solution have been widely used to assess increase in acidity due to the action of bacteria. Titration of a known volume of milk (10ml) is carried out against 0.1 normal NaOH to the commonly used phenolphthalein indicator end point at about pH 8.3. Concentration and dilution of milk, heat treatment given to milk and the amount of phenolphthalein influence the acidity of milk.