Good stuff so far Julian,
I think it needs to be in the plural though as there is more than just one free fatty acid.
Used vegetable oil, on the other hand, will contain Free Fatty Acid(s) in varying amounts largely depending on how, and for how long, it has been used.
Free Fatty Acid(s) play no useful part in the biodiesel reaction and need to be removed. This is done by adding additional catalyst with which they will react to form soap which is removed later as part of the production process.
Titration is a test that simply determines the amount of Free Fatty Acid(s) in the oil
and are you doing just turmeric or wiill you add phenolpthalien too?