First, I apologize if this question has been covered, as I have seen that it seems to be a repeated topic. However, I could not find the answer I'm looking for.
The big question is, WHEN do I do a diacetyl rest?
The general consensus seems to be when fermentation is at 75%. But how do I know when it's at 75%? The logical assumption is, check the gravity, but in a previous thread, I read that you shouldn't check the gravity too often. Is the rate of fermentation even linear? I'm guessing it's probably a function of LN, so it would be extremely difficult to predict the rate of fermentation in order to calculate when it's at 75%, so as to limit the number of times I have to stick my wine thief into my beer.
So, is there a way to tell when it's at 75%? When the krausen starts to fall? After it's fallen? When the airlock starts to slow? I'd think that after the krausen has fallen, fermentation is a lot further than 75%.
I've also heard, "After N days." Well, if the fermentation is strong and rapid, it could be completely finished in N days. That's something that would vary too much for a simple rule of thumb like "after N days".
How do I know when to pull my lager out of my fridge and stick it somewhere warmer for a couple days? Thanks in advance.