In a first aspect, systems and methods for producing biodiesel fuel include a modular production unit incorporated onto a single platform or into a housing for ease of relocatability. The modular production unit preferably includes a mixing unit, a reactor unit, a separation unit, a distillation unit, and a filtering unit, all incorporated onto or into a self-contained platform or housing that is able to be easily relocated. In a second aspect, the modular production unit is combined with additional fixed and / or relocatable components to provide a biodiesel processing plant. In a third aspect, a raw materials processing system and method includes a roller barrel adapted for recovery, transportation, and introduction of recycled oil feedstock into a biodiesel manufacturing process. The raw materials processing system preferably includes a hot box for filtering and heating the raw recycled oil feedstock.