Alright defatting occurs when you add your non-polar (shellite, naptha, lighterfluid. hopefully not the last one its impure and the first two are dirt cheap) to your acidic soup after the boils. Your spice will be in the aqueous acidic layer (soup) as a salt and therefore won't be soluble in your non polar solvent so it will only pull fats and oils out not the goodies. The ammount is up to you but it depends on batch size. 3x125ml would be good for 500g. You will extract much more shit out of there by breaking it into 3 lots rather than one big extraction.