[bassriverbrewer]

Whats the best time to do a diacetyl rest?  Is it when fermentation is winding down or after signs of fermentation has stopped?
I made a munich Dunkel with wlp 838 and after 10 days the krausen subsided and activity is very slow in the fermenter. There is still a thin layer of clean foam on the whole surface and the airlock bubbles every five seconds.  I'm planning on racking this into a secondary and putting in the fride to lager for three to four weeks

[chezteth]

You want to do the diacetyl rest when the fermentation is winding down but not completely done.  I would do a diacetyl rest before transferring to the secondary fermenter.  Warm the fermenter to the mid to high 60's and keep at that temp for 2-3 days.  After the diacetyl rest is complete then transfer to secondary and lager.

Happy Brewing,
Brandon

[tom]

Technically when the fermentation is 2/3 done. Although all lager yeasts don't reqiure one.
(If your attenuation is going to be ~75%, then 2/3 of 75% = 50% , so when the gravity reaches 50% of the o.g.)

[James Lorden]

I shoot for about 1.5 degrees Plato above final gravity (6 gravity points).  You can calculate your expected final gravity by doing a fast ferment test.  Kai advocates this all the time, you can do search for the method.