It's hard to find technical info, but IIUC it's there is not "fat and sugar" inside the fuel tanks. They burn horribly and will fill the engines with soot and have nasty properties when the temperature change like beeing too thik or too thin. IIUC it's a mix of biodisel and ethanol.
The fat has three fatty acids bounded with a glicerine. To make biodisel you ust split it in the tree parts and bound each one with a methanol. The new compound is smaller and easier to burn correctly.
The sugars are split in smaller parts, and after some steps you get ethanol that is a nice liquid instead of a nasty power, so it's easier to pump.
Saying that thee airplane uses "fat and sugar" is like saying that inside a computer is a "sand castle".
