When is the appropriate time for diacetyl rest?

I've read many conflicting suggestions about the correct timing for a diacetyl rest for a lager. Do I do it:

A) at the end of primary 48-72 hours BEFORE racking to secondary for lagering or

B) immediately AFTER racking to secondary and then waiting 48-72 hours before lagering

Help is appreciated.
:rockin:

I've never lagered, but my understanding is that the rest is done as primary fermentation is winding down and before racking to secondary.

See also https://www.homebrewtalk.com/wiki/index.php/Fermenting_Lagers

"To remove any diacetyl that may be present after primary fermentation, a diacetyl rest may be used. This rest at the end of primary fermentation consists of raising the temperature of the beer to 55-60 °F for 24 - 48 hours before cooling it down for the lagering period."

"One thing to remember, if you incorporate a diacetyl rest, is to rack the beer - or in a unitank fermentation, draw off the yeast - before you allow the temperature to rise."

"you warm up the beer towards the end of secondary fermentation, the diacetyl level will drop pretty fast. Bring the beer up to the low sixties for 48 hours. Then drop the temperature back down to lager temperature by about 2 degrees per day. "

Take a gravity reading and try to hit it at about 1.020, while it is still in primary fermentation. Warm it up to ale temps. Let it drop to FG and then let it sit for a couple days after that. Rack to secondary, lager.

klnosaj said:

"To remove any diacetyl that may be present after primary fermentation, a diacetyl rest may be used. This rest at the end of primary fermentation consists of raising the temperature of the beer to 55-60 °F for 24 - 48 hours before cooling it down for the lagering period."

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Increasing temperature allows yeast to be a little more active. This yeast will consume the diacetyl. Going to a secondary (pulling beer off of yeast) and going cooler (which can cause yeast flocculation) would reduce the yeasts ability to consume the diacetyl.

I know this threads is about a lager. However, the key is increasing the temperature while still having the bulk of yeast. If you were doing an Ale and tasted diacetyl, you could increase the temperature as well, not lower it to 55-60.

Ales can benefit from cold conditioning as well. Since I keg/force carbonate, I don't have to worry about yeast dropping. If I was naturally carbonating, I don't know if cold conditioning would cause too much yeast to drop.

Sorry a little tangent here.

t_met said:

Increasing temperature allows yeast to be a little more active. This yeast will consume the diacetyl. Going to a secondary (pulling beer off of yeast) and going cooler (which can cause yeast flocculation) would reduce the yeasts ability to consume the diacetyl.

I know this threads is about a lager. However, the key is increasing the temperature while still having the bulk of yeast. If you were doing an Ale and tasted diacetyl, you could increase the temperature as well, not lower it to 55-60.

Ales can benefit from cold conditioning as well. Since I keg/force carbonate, I don't have to worry about yeast dropping. If I was naturally carbonating, I don't know if cold conditioning would cause too much yeast to drop.

Sorry a little tangent here.

Click to expand...

So why this: "One thing to remember, if you incorporate a diacetyl rest, is to rack the beer - or in a unitank fermentation, draw off the yeast - before you allow the temperature to rise," from Dave Miller at Brewing Techniques?

Perhaps never.

https://www.homebrewtalk.com/f128/lagering-keg-289979/index3.html#post3640375

klnosaj said:

So why this: "One thing to remember, if you incorporate a diacetyl rest, is to rack the beer - or in a unitank fermentation, draw off the yeast - before you allow the temperature to rise," from Dave Miller at Brewing Techniques?

Click to expand...

From Jamil Zainasheff & John Palmer's Brewing Classic Styles pg46: "To perform a diacetyl rest, warm your beer up about 10F above the fermentation temperature and hold it there until fermentation is complete. This keeps the yeast active and gives them a chance to eliminate the diacetyl. Then rack the beer to a 5-gallon carboy or Cornelius keg for lagering."


However the Homebrew talk wiki and BYO says we're both right. BYO states: The presence of sufficient healthy yeast during aging increases diacetyl removal. Yeast remove diacetyl much faster than they produce it. Sending the beer into secondary fermentation or maturation with some yeast still in suspension should be sufficient to reduce the diacetyl in a timely manner. The majority of the yeast will sediment. The yeast that remains in solution will hopefully be sufficient for maturation.


Whether you move it to the rise before racking or after, I'm reading isn't the critical step. It's more to allow the yeast to remove it faster than it produces. You're point is there is enough yeast in solution. I can see that. I prefer to do it the Zainasheff way so that I can cool it down, have some of the yeast floculate, then rack over leaving more yeast in the primary.

wildwest450 said:

Perhaps never.

https://www.homebrewtalk.com/f128/lagering-keg-289979/index3.html#post3640375

Click to expand...

Correct, you only need to do a diacetyl rest if you can taste it. If you fermented at the right temperatures with right pitching amounts and right amount of oxygen, you'll produce a clean tasting beer without the diacetyl rest.

Hmmm. I'm a little confused myself. I brewed my first lager on Saturday evening. OG was 1.050, a Vienna using WY2308 Munich Lager (4 qt starter). I pitched and held at 52F. I saw activity when I woke up the next morning so I dropped the controller to 49F. It's stayed there for 4 days, happily bubbling along at a fairly slow rate.

I checked it visually today (it's in a bucket). Airlock activity dropped way off, so I took a gravity reading. All the way down to 1.016 already. Some evidence of krausen, but not much left up top. Tasted maybe something like diacetyl, but I had planned on doing a rest anyway. Just not so soon.

Sounds like its almost done, so I suppose I should start raising the temps now? Is it too late? Guess I'll hold them around 60 for a few days. After this is complete, rack right away to keg and lager for 6 weeks?