Alkyd coatings are produced in two processes; fatty acid process and the alcoholysis or mono-glyceride process. Higher quality, higher performance alkyds are produced in the fatty acid process where the composition of the resulting resin can be more precisely controlled. In this process an acid anhydride, a polyol, and an unsaturated fatty acid are combined and cooked together until the product has achieved a predetermined level of viscosity. Penta alkyds are made this way. More economical alkyd resins are produced from the alcoholysis or glyceride process, where end-product quality control is not as paramount. In this process raw vegetable oil, high in unsaturated component, is combined with additional polyol and heated to cause transesterification of the triglycerides into a mixture of mono- and diglyceride oils. To this resulting mixture acid anhydride is added to build the molecular weight of the resin into roughly the same product as in the fatty acid process. However, the alcoholysis process (also known as the glyceride process) produces a more randomly oriented structure. To remove the water produced as a by-product and to increase the reaction rate, surplus phthalic anhydride was added. Water was thus removed with the unreacted acid by heating the bulk to a temperature needed to do this. It meant that the reaction was not as controllable as would be desired. A new process was introduced, in which Xylene was added to produce an azeotrope with the water. This gave greater control at a lower temperature; it also produced resins at a lower viscosity, useful in making high solids paints. The process was known as the AZO process. In both cases, the resulting product is a polyester resin to which pendant drying oil groups are attached. At the conclusion of each process the resin is purified, diluted in solvent, and sold to paint and varnish makers.