What juice are you talking about?
You mean pot liquor? My usual method is to steam the greens to wilt them, squeeze out the liquid, chop, sauté with onion / garlic / pork products / whatever, add the liquid back, and simmer.
If there’s too much pot liquor, add it to soup.
In the South we call it “pot likker” and we’ve been known to drink it, especially with some corn bread crumbled up in it.
That’s an interesting way to cook greens. I’m gonna’ try it. I usually brown the pork product in the pot, remove, drain some of the fat, add a little cooking oil, sauté onions, garlic, crushed red pepper in the same pot, then start adding washed greens on top a little at a time, tossing, then add pork, liquids, simmer, salt at the end, if needed.