*Feedstock
**Microbial oil
***Oleaginous microorganism
**Palm oil
**Soybean oil
**Coconut oil
**Vegetable fats and oils
**Jatropha
**Animal fat
**Waste oil
Common feedstock used in biodiesel production include:
*Yellow grease (recycled vegetable oil)
*Vegetable oil fuel
*Tallow
Lignocellulose generates byproducts that act as enzyme inhibitors, such as acetic acid, furfural, formic acid, vanillin, and these chemical inhibitors affect cell growth.
Recycled oil is processed to remove impurities from cooking, storage, and handling, such as dirt, charred food, and water. Virgin oils are refined, but not to a food-grade level. Degumming to remove phospholipids and other plant matter is common, though refinement processes vary. Water is removed because its presence during base-catalyzed transesterification results in the saponification (hydrolysis) of the triglycerides, producing soap instead of biodiesel.
A sample of the cleaned feedstock is then tested via titration against a standardized base solution, to determine the concentration of free fatty acids present in the vegetable oil sample. The acids are then either removed (typically through neutralization), or are esterified to produce biodiesel (or glycerides).