Diacetyl resting

[bmantzey]

I was making a document for myself outlining the steps required for brewing, just to serve as a minder for reference. When I got to the part regarding lager fermentation, I hit a few bumps of uncertainty.

Please correct me when I'm wrong. I'll just paste my ramblings:

"For lagers
Take gravity readings twice daily ??? with very well sanitized wine thief, test jar, and hydrometer.
When gravity is 5 points to target FG, raise the temperature to 65 - 70 ??? for a diacetyl rest. Leave it at this temperature for N days. ???
After diacetyl rest, allow primary fermentation to conclude for N ??? days."

I say twice a day so I can accurately predict when the correct gravity will be reached to begin the diacetyl rest. If I'm carefully sanitized, I suppose it's not too often.

I'm not sure about how many points to FG at which I should raise the temperature, exactly what temp I should raise it to, or for how long I should leave it at that temp.

 

[Yooper]

I was making a document for myself outlining the steps required for brewing, just to serve as a minder for reference. When I got to the part regarding lager fermentation, I hit a few bumps of uncertainty.

Please correct me when I'm wrong. I'll just paste my ramblings:

"For lagers
Take gravity readings twice daily ??? with very well sanitized wine thief, test jar, and hydrometer.
When gravity is 5 points to target FG, raise the temperature to 65 - 70 ??? for a diacetyl rest. Leave it at this temperature for N days. ???
After diacetyl rest, allow primary fermentation to conclude for N ??? days."

I say twice a day so I can accurately predict when the correct gravity will be reached to begin the diacetyl rest. If I'm carefully sanitized, I suppose it's not too often.

I'm not sure about how many points to FG I should raise the temperature, exactly what temp I should raise it to, or for how long I should leave it at that temp.

Check the SG twice a day is more than overkill! I just keep an eye on the fermenter, and when activity slows way down, but doesn't stop completely, then it's time for the diacetyl rest. You want the yeast to be still active, if possible, but it isn't an exact thing.

Generally, you'd raise the temperature when you're about 75% to FG. So, if you were expecting something like 1.012-1.015, then 1.020-1.025ish would be appropriate, depending on the OG.

As far as how long to do the diacetyl rest, it's good to do it until the beer is at FG and no diacetyl is detected in the sample. I like to taste it, and if it's got ANY oiliness or slickness in the mouthfeel or on the teeth or tongue (those are signs of diacetyl, in small amounts), then to extend the diacetyl rest.

 

[bmantzey]

Thanks for the reply. That's seems pretty intangible still though. When it "slows way down"? Hm.

Maybe I just have to experiment with it. Maybe I should test as often as I need to test it when it appears to be slowing, not 2x per day. Once I become familiar with what the fermentation should look like, I shouldn't need to test it because I'll just know from experience. Hmm. Hmm. Hmm.

 

[MBTB]

I bottled a lager this evening that did not get a d-rest and didn't detect any diacetyl. I always leave my lagers in primary for 4 weeks with no D-rest. Again, no diacetyl, even with yeasts that recommend a d-rest.

 

[osagedr]

A diacetyl rest may not always be necessary, but it is simple and costless to do and may save you a great deal of time and trouble.

If you want to take a crapload of gravity readings for recreational purposes, go for it. I seem to recall that in their book "Yeast" Chris White and Jamil Zainasheff recommend a d-rest around 5 points above expected OG. I usually do them significantly higher, in the 1.020 to 1.025 range that Yooper suggested. It's a good way to ensure fermentation finishes off strong (by far the most common mistake new lager brewers make is underpitching) and I've not encountered any negative flavour effects.