Saponification value determination involves measuring the amount of alkali required to saponify a known mass of fat or oil.
Weighing a fat/oil sample, saponifying it with alcoholic KOH, and titrating the surplus alkali with HCl while using phenolphthalein as an indicator are the steps in the lab process to find the saponification value.
Due to residual alkali from insufficient saponification or neutralization, a larger volume of HCl is needed to titrate the blank (no sample) than the sample. By assisting in the determination of the excess HCl required to neutralize any residual alkali, the blank ensures correct characterization of the fat or oil sample and precise measurement of the saponification value.