The cooking oil used in the biodiesel process is clear vegetable oil and is filtered to 15 microns (a human hair is 100 microns thick) and heated to 145F before it is made into biodiesel. During this process it is mixed with an alcohol and caustic to split the glycerin from the oil molecules. Biodiesel, which is a biodegradable substitute for petroleum diesel and home heating oil, is then formed!
The glycerin byproduct is then distilled at temperatures above 260F over a period of about 48 hours, to remove excess alcohol. This effectively sterilizes it before it undergoes a further process to make the final product. In contrast, an autoclave used to sterilize medical equipment uses temps of 250F for 15-20 minutes.