How important is a diacetyl rest?

[fidcastro]

I just racked my Oktoberfest to secondary. I think I am at about 60% of the fermention. I have two questions:

1) How important is the diacetyl rest?

2) When should I do it?

[fidcastro]

P.S. I'm not quite sure how I am going to maintain 55 degrees. my kegerator is good for about 44 at the most. Any suggestions would be quite appreciated.

[danno]

ever tasted diacetyl? do you like butter? you should do it prior to racking to the secondary, since that leaves the most yeast to reabsorb the diacetyl. since it sounds like you missed that opportunity, you may want to leave the beer at room temp for a couple more days, then lager.

after the diacetyl rest, you should lager as close to freezing as you can get. 55º is for fermenting, 33º is for lagering. take your kegerator to its lowest setting and see how close you can get to freezing...

[brewmonkey]

The diacetyl rest is an important step in the lagering process. It should be done when you are about 75-80% complete with primary by raising the temp of the beer to 60F and hold it there for 24-48 hours. Since you will still have active fermentation simply moving the carboy to ambient temps it will come to 60F easily. Once the rest is over simply go ahead and bring the temp back down to your conditioning temp. OI prefer to step down 1-2 degrees every 1-2 hours until I hit 40 where I hold it for 48-72 hours before stepping down to 33F and holding it for 4-6 weeks.

[BluesHarp]

I followed all the above procedures and still ended up with some diacetyl; I read an article in BYO about late diacetyl (even appearing post-lager).

They recommended doing a mini-krausen with a 2qt yeast starter added at high krauesen, leaving it at 60° for up to two weeks, then bringing back to lagering temp to drop out the new yeast.
I hope I can get it done in time...I will have to force carbonate by shaking, I think, to buy some extra time.

[brewmonkey]

While yeast is one way diacetyl is formed in beer it is not the only way. The gram positive bacteria Pediococci and certin strains of Lactobacillus are both responsible for diacetyl and in those cases there is nothing you can do.

The good news is that when diacetyl is formed from bacteria it is a MUCH different taste then from yeast, it is very nasty and as time passes it gets much worse.

I am not saying this is your issue but just using this discussion to introduce more information on the subject. Here (http://www.brewingtechniques.com/library/backissues/issue1.2/fix.html) is a good read from the guys at Brewing Techniques on the subject that should be a good primer for further discussion on the topic.

[BluesHarp]

Brewmonkey...Interesting read, even though my chemistry is a bit rusty. The flavor in my beer is not at all unpleasant, just not right for a Marzen. It is definitely butterscotch, but not the "movie popcorn artificial butter" flavor I have heard described.
However, since I am not completely happy with the taste, I'm going to give the yeast addition a try.

One question - the BYO article says to add the new yeast at full krausen and let it work at 60° F; the article you linked mentions adding it to beer that is in "cold storage"...what are your thoughts on this?

[brewmonkey]

I would go for bringing the temp up to 20C and pitching at high krausen. Allow the fermentation to complete and then hold it for 48-72 hours testing it along the way for flavor threshold.

[BluesHarp]

Pitching tonight...beer is at about 60° F. Are you saying that after fermentation I should hold at that temp before crashing it to lager temp?

[fidcastro]

After the diacetly rest, should I rack again before lagering?

[HogieWan]

if you racked before the rest, no. Though most people (from what I understand) leave the beer in primary for the rest and then rack. The reason is that the yeast reabsorb the diacetyl and there is more of the yeast in the primary.