An improved process for making bioderived propylene glycol from a feed composition including at least one of lactic acid, glycerol, a five carbon sugar, a five carbon sugar alcohol, a six carbon sugar and a six carbon sugar alcohol, wherein production of four carbon and higher diols is reduced by adding base after the initiation of the reaction. In preferred embodiments, the process pH and other process conditions are initially established at targeted values for obtaining the highest conversion for a given catalyst consistent with the production of substantially no pentanediol byproducts in the product mixture, and base is added thereafter to control the process pH proximate to the initially targeted value.