This disclosure relates to a continuous process for preparing a grease thickener product in which operating conditions of the continuous process can be varied to obtain desired grease product properties. The process includes: (a) introducing a C3 to C30 hydroxy fatty acid or a C3 to C30 hydroxy fatty acid ester, and a metal base into a reaction zone; (b) operating the reaction zone at a temperature between 100° C. and 240° C. to react the C3 to C30 hydroxy fatty acid or the C3 to C30 hydroxy fatty acid ester, and the metal base, to produce a grease thickener product; (c) introducing the grease thickener product of step (b) into a flash chamber zone; and (d) operating the flash chamber zone at a temperature sufficient to remove volatiles from the grease thickener product of step (b). The continuous process conditions afford a production throughput of grease thickener product of greater than 8,000 pounds per hour.