i use caffenol C all the time,
it works well for my fun in the darkroom ...
i just make sure to get gut rot instant coffee.
the vit. c is the expensive stuff ..
i get mine at whole paycheck,
since we don't have a trader joe's around here

i do cheat a little bit ... sometimes i add some
spent print developer or some straight print developer
to boost the contrast a tiny bit. i usually add about "a splash"
not sure exactly what that measure is exactly, seeing
my coffee is " a big dump",
laundry det. is "a medium dump" and
vit c is "a little dump"

(i stopped using true "international measurements" a while back )