Try letting go of the bar juuust a tad sooner. I had the same issue after my 2nd bimbo potion--no matter what it would turn brown. I checked the guide, it messed up. I checked here, it still didn't help. Ultimately, I just tried until I got it and found I had to let go sooner than I was, add the next ingredient, and do the same for the next stir meter.Just started playing this a couple days ago - but I seem to be stuck on the alchemy making mini-game at the academy. I'm following the recipe - but when the green bar just touches the black bar on to bottom, it immediately turns brown.
Any one else have/had that issue? I'm trying to go down the bimbo route.
TlDr: Let go of the button just before it hits the mark. It may seem too soon but try.