Confused about Diacetyl rest

[morethanworts]

Hi there,

I have read at least one source that says you should let fermentation finish before giving lager a diacetyl rest... http://www.homebrewing.org/How-to-Make- ... _42-1.html

...and one that tells you to to do it 3/4 of the way through primary (though it still says this somehow requires experience to know exactly when)... http://www.howtobrew.com/section1/chapter10-4.html

I don't get this aspect of the second one (Palmer) at all: if more diacetyl was created when the brewer has started at room temperature and then lowered it, then why doesn't it just produce more again when we bring the heat up for the 'rest'? :wha:

My primary is currently 3/4 of the way through, so what's the right way please???

 

[Aleman]

Diacetyl is typically produced early in the fermentation when the yeast are actively dividing. Later in the fermentation it is still produced but as the yeast are not dividing at this stage, more is reabsorbed than produced. The reason for raising the temperature is to stimulate the yeast and make sure that they enter this use up the by products phase while they are able to do so.

Personally I tend to go for the day or so before the end of fermentation approach, so there is some energy available to drive the processes . . . it also ensures that fermentation proceeds to completion.

 

[pittsy]

Yet again top advice from Aleman :thumb:

 

[morethanworts]

Sounds like top advice, and he is the Aleman after all!

Ok, this is the plan...
OG 1.045
SG @ 6 Days was 1.030
SG @ 13 days was 1.018 (yesterday)

If it continued to slow at the same rate (at the same temperature) it could be another 6 days or so to 1.010 (as per kit's rough target), though if it's going to stop higher, probably sooner.

It's been between 10-13C throughout, currently nearer 13. So I've clicked the STC 1000 up half a C and will continue to do so periodically over the next day or two until I'm at 17C(?) at which point it should still have a small bit left to ferment out. I'll keep it there for a couple of days before lagering in demijohns (probably 1.012 or lower and stopped)

 

[morethanworts]

OK

A further question please, seeing that fermentation has gone very slowly since my last post...

So after reaching 1.018 down from OG 1.045 in around two weeks at 12C or so, I raised the temperature over a couple of days and have held it at 17-18C for 5 days. It has only moved 5 points in the last week [EDIT - even at the higher temperature], down to 1.013 now, with a few small bubbles still rising in the sample tube.

[I know diacetyl rests are usually 2-3 days, but it had slowed so much that I decided to keep the fermentation as strong as possible up to the end]

Would you move it to secondary now and keep it warm for a few more days before cool storage, or leave it on the bulk trub for a bit longer?