This is sperm from your male quail or sperm mixed with lubricant. If you lift your male up turn him over and lightly press his privates (the lump under his tail) you'll see the foam ooze out and know he is ready for mating.
Sorry we might be getting a bit deep into it here for some but ... that brown stuff is that poop and when he poops the sperm just happens to come out with it, because they both came out at the same time?