For high acid value oils, alkali- and then acid-catalyzed transesterifications were used (Sprules and Price, 1950). The free fatty acids were neutralized with alkali to form soap during the reaction. After the triglycerides were converted to esters, 5% by oil weight of sulfuric acid was added to neutralize the alkali catalyst, release the free fatty acids from the soap formed and acidify the system. The mixture was then transesterified for 3–4 h to make esters from the free fatty acids. The mixture was neutralized with an alkali salt such as calcium carbonate, filtered and freed of methanol by distillation. After the glycerine was separated, the esters were washed with warm water and distilled under vacuum of 133 Pa.