A process for forming a color and odor stable polycarboxylic acid or polyhydroxy acid is provided. The process is carried out by fermenting a mixture containing a substrate which can be converted by fermentation into a polycarboxylic acid or a polyhydroxy acid, an organism capable of transforming the substrate by fermentation in a fermentation medium containing a source of carbon and energy, a source of inorganic nitrogen, a source of phosphate, a metal, a biotin which is substantially free of particulate matter and bacteria.