Fats are examples of esters:  They are made of fatty acids (like oleic acid) and the alcohol glycerol.  Soaps are salts of those fatty acids sodium salts being used for washing.

* Dissolve  10 drops of oleic acid in 1 ml of methylated spirit and add one drop of  phenolphthalein solution.
* Shake while you add drops of 1 molar sodium hydroxide.  Neutralisation is finished as soon as the red colour does not longer disappear.