It takes a lot of patience to tame a feral cat, the younger the cat the
easier it is to tame. I have a lot of strays around my house, some I can
tame some not, seems like the males are easier than the females, don't
know why that is.  
So the way I work with them is when you put the food out, try to stay
close to the food, when the cat comes around talk to it sweetly and
softly, for a time, in time it will respond to you talking to it, then
put your hand out for it to sniff you hand, all the while, doing
everything very slowly and gently. As the cat begins to trust you, it
will eat with you sitting there, then is when you can try to pet it,
most cats LOVE being petted, once they decide to trust you.  ALL of this
takes time, I can't stress that enough, I wish you the best of luck,
it's a wonderful feeling to tame one of these creatures. God bless you
for trying it can be done.

Aimee