I just brewed my 2nd batch of beer. The fermentation to about 3 days to start doing anything, and I was about to pitch more yeast when the airlock started bubbling and I got some foam on top. Today, about 10 days later, I checked on it and it is bubbling vigorously (not just the airlock, but the beer itself) and has gone from semi clear to opaque. The head on the beer has mostly subsided. What is happening?
You've (almost) got beer. When the krausen falls, the beer gets muddy.
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The beer is still fermenting. Leave it alone for at least another week if not longer.
Did you take a starting gravity reading? The only real way to tell if the yeast is done working (even if there is not any active signs of fermentation) is to take a gravity reading at the beginning and a few weeks later. If the gravity has dropped around 75% or more then it is good to bottle.