Abstract: A process involves heating waste grease in a first separation chamber to separate it into a primary oil, aqueous, and solid phase and decanted the primary oil phase by flowing it upwardly and over a liquid impermeable barrier and into a second separation chamber. Components of the primary oil phase are separated into a secondary oil, aqueous, and solid phase. The secondary oil phase is decanted by flowing it upwardly and over a different liquid impermeable barrier and into a heating chamber. In the heating chamber, the secondary oil phase is heated to a temperature sufficient to separate components of the secondary oil phase into a tertiary oil phase, aqueous phase, and solid phase. The tertiary oil phase comprising brown grease is extracted. The remaining tertiary aqueous and solid phases in the heating chamber may be heated again to produce a tertiary oil phase comprising additional brown grease.