I have Bohemian Lager fermenting (2124) at 56F-57F for 5 days, now I am at 1.016 and the pleasant smell turn into sulfur like smell. How you determine when to start d-rest by time, gravity ?
When gravity stabilizes, just before lagering. A lot of people say to do the d-rest at 58F, but I like to kick it up to 65-68F to make sure, especially if the initial ferment was on the warm side (like 56F). 48 hours is plenty.
I'd let go at least a week after gravity has stabilized then let it free rise to 58 and hold it for a few days...patience grasshopper. I let my lagers go 3 weeks minimum befor I go poking at them. Then I make informed decisions, but damn it's so tempting to fiddle with them. It's the constant struggle.
Two common approaches to d-rests include performing it once final gravity has been reached or starting it when about 70% of the extract has been fermented. The latter approach helps encourage full attenuation. For a lager, I generally raise it up to the 64-65F range for 2 days.
I just got this whitelabs Diacetyl Time Line suggested to start d-rest 2 to 5 gravity points from the target terminal gravity. But I rather have homebrower hands on experience then the "boys in the lab"
