Diacetyl rest?

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Cmiley

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Doing my first lager and am curious as to how you know if the Diacetyl is gone. I have read to take a gravity test after rest. How much should the gravity change from the OG to know if the rest has worked? Also I have read to take a taste but I am not sure what I am tasting for. Also should the diacetyl rest take place while still in the primary fermentor or after it has been racked to the secondary? My lager sits at 48 to 50 degrees F now and I plan to do the rest for 3 to 5 five days between 53-55 degrees F. Any information on this would be of much help. Happy Brewing, Chris.
 
From Palmers how to brew:

Diacetyl is most often described as a butter or butterscotch flavor. Smell an unpopped bag of butter flavor microwave popcorn for a good example. It is desired to a degree in many ales, but in some styles (mainly lagers) and circumstances it is unwanted and may even take on rancid overtones. Diacetyl can be the result of the normal fermentation process or the result of a bacterial infection. Diacetyl is produced early in the fermentation cycle by the yeast and is gradually reassimilated towards the end of the fermentation. A brew that experiences a long lag time due to weak yeast or insufficient aeration will produce a lot of diacetyl before the main fermentation begins. In this case there is often more diacetyl than the yeast can consume at the end of fermentation and it can dominate the flavor of the beer.
 
While my lager is in my primary (after 3 weeks of fermentation), I raise temps to 60-ish (give or take) depending on time of year, etc. to remove the diacetyl. After, I rack to keg for conditioning. That's just my 2 cents. Definitely raise temps past your fermentation temps at least 5 degrees to get rid of the butterscotch off-flavor you could get at the very end of fermentation. You don't need to measure as long as you see some airlock activity and then watch it slooooow down gradually over the next few days.

Sounds like you are on the right track!
 
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