A mixture of mono‐, di‐ and triglycerides was obtained when beef tallow was reacted with glycerol using lipase enzyme as a catalyst. The reaction was carried out batchwise in a small vessel with agitation by magnetic stirring. The yield of monoglyceride (MG) was greatly influenced by the reaction temperature—at higher temperatures (48–50°C) a yield of approximately 30% MG was obtained, while at lower temperatures (38–46°C) a yield of approximately 70% MG was obtained. A sharp transition was observed between the high and low yield equilibrium states. The temperature at which this transition occurred is called the critical temperature (Tc) and was found to be 46°C in the case of tallow. During the course of the reaction, when approximately 40% MG had been synthesized, the reaction mixture became solid but the reaction continued until approximately 70% MG had been synthesized.A yield of 70% MG also was obtained with tallow at 42°C when a glycerol/tallow mole ratio ranging from 1.5 to 2.5 was used. The free fatty acid content at equilibrium depended on the water concentration in the glycerol phase and varied from 0.5% to 11.0% when the water content ranged from 0.6% to 12.5%. Above 8% water content, the yield of MG was reduced. Of the commercially available lipases that were investigated, lipase fromPseudomonas fluorescens orChromobacterium viscosum resulted in the highest yield of MG.