As the colonies mature, starve them of nitrogen . The cells react to the low nutrient supply by entering survival mode and producing extra fats. When they´ve created enough fat, collect the cells and break them apart . Filter out the large organelles and cell membranes, and then use solvents like methanol to separate out the fats from the water-soluble proteins and sugars . Purify the collected fats, and evaporate the solvent . Finally, put the fats in a chemical reactor to transform them into biodiesel (a process called transesterification) .