< I have never heard of such. How does fermentation denature? >
don't know exacty. but the clumping of cultured milk comes from protein
denaturing.

< Is IGF protein or lipid? It seems to me like other steroids it would a
lipid
 molecule.>
IGFs are peptides, hence proteinous/nitrogenous compounds.
having said that, I am now no longer sure whether i merely assumed, or read
an authoritative
opinion, that the culturing process definitely denatures the IGFs along with
the caseins.

andrew