diecetyl rest for my lager, why?

okay, I have been reading up plenty about diecetyl and the diecetyl rest. it seems easy enough, just turn my fridge off (I have a dedicated mini fridge for fementation), and wait a couple of days before cold crash/lagering.

but I started thinking, why? why would you purposely try to create diecetyl just to get rid of it?

I used s23 lager yeast (yes, I know, not the best, it was all I had), and am fermenting in the 'optimum range'. shouldn't that keep diecetyl at bay?

plenty of articles out there on what to do, and what happens, but once I started looking for the reason why its done (other than to produce diecetyl, just to get rid of it), I couldn't find any info.

help?

 

You wouldn't.

The objective is not to create diacetyl with a diacetyl rest but to speed along its elimination. Warm temperatures allowing the yeast to metabolize this unwanted fermentation product more rapidly.

As with many things prevention is the best form of cure and there are ways to target minimizing the production of diacetyl.

 

link: http://byo.com/stories/item/303-brewing-science-controlling-diacetyl

to me, that sounds like I am purposely creating diacetyl by raising the tempature. I totally understand the prevention thing, I had assumed that had something to do with it. I understand that the yeast will work quicker at higher temps, but according to that quote, more diecetyl can be created. am I not reading that correctly?

I have no problem doing a rest. Hell, all I have to do is turn off my fridge and leave the door open for 2 days. Just trying to understand it all (knowledge=power).

p.s. maybe i should learn how to spell the damn word...

 

I think, in the words of BYO, this is the mindblow you're missing:


"Not only do yeast produce the precursor to diacetyl, they also consume the diacetyl that is produced and enzymatically reduce it."


Different things happen at different phases of fermentation. You don't want to warm up your lager yeast at the beginning or amid peak fermentation activity. But once fermentation has neared completion, that is when you would intentionally raise the temp for a diacetyl rest. You won't be creating diacetyl at this point - if that had happened, it would have been a result of the lag / exponential growth phase.

 

From the article "Even though the diacetyl can’t be tasted, however, the beer might contain high levels of the precursor, acetolactate, which can be converted to diacetyl. Once the yeast is removed, there is no way to get rid of the diacetyl."


The rest is not just for the yeast to eat the diacetyl but also to try to convert the acetolactate to diacetyl while the yeast is still active so that it can be consumed and not cause off-flavors later. The conversion of acetolactate to Diacetyl does not require heat and can happen later after cold crashing or bottling/kegging.

 

I think this is what I was missing the most. I thought when the temps raised, more was created (on top of what was already in the beer).

Now, the 'mind blow' makes more sense. thank you!

I did not know this either! I love this forum, such a wealth of knowledge.
thank you all for the help, I believe I understand diacetyl, acetolactate, and what happens a lot clearer than I did a couple of hours ago.

So then, next question: I do the diacetyl rest for 48 hours. Do I cold crash, then rack to secondary to lager? Or should I rack to secondary then cold crash/lager?

 

I vote neither. (I am not a proponent of using a secondary.)

 

Seen a lot of different opinions on this. Consensus seems to be to lager off the primary yeast cake.

How long would you lager in primary?

 

So how long would you lager for in primary? Consensus seems to be to take the beer off the yeast cake and lager in a secondary to avoid yeasty flavours.

 

I'd lager in the keg.

 

I wouldn't

I get my lagers off the yeast and into a keg as rapidly as practical. Usually at around the 2 week mark. They lager at ~34F in the keg while carbonating.

If you bottle the same can be done in the bottle after carbonation has occured.

 

I agree completely, lager in the keg and skip secondary.

 

As soon as I get home my first lager will be pulled from the fridge to start it's diacetyl rest.

Just wanted to thank ya'll again