Help with math? When to do the D-rest?

[ChandlerBang]

I have a Brewer's Best Maibock sitting in the swamp cooler right now. It has been cold enough since I brewed it (Christmas night) that I have kept it right around 50. We had a warm up and now the damn thing is at 60!

OG was 1.070 (right on target)
Est FG 1.016-1.019
Right now it is at 1.036 and happily fermenting.

The question is do I drop a bunch of ice and try to get the temp back down?
Or, is it far enough that I can bring it up to 65 degrees for the D-rest?

EDIT: And which way will lead to less off flavors?

 

[jigidyjim]

D-rest is supposed to be 75%-80% done fermentation. You are at 65%... I'm not sure what the right answer is. Curious to hear from more experienced lager brewers, I've only done one, and it's still lagering.

To whoever answers, I'd also be interested in hearing some more explanation. My understanding is that at warm temps, lager yeast have off flavors, but at 80% done, the yeast is not doing a whole lot, so any off flavors are mitigated (and offset by the fact that you are cleaning up diacetyl, which is important)?

 

[martinworswick]

i wouldn't cool it back down again as the yeast don't like swings in temperature.
i'd wait until its closer to the estimated fg and warm it by a few more degrees for the d-rest
as for the off flavours i believe most of them are created at the beginning of a ferment so you should be good.

 

[JNye]

i am in almost the exact situation/timeline, except my temps only got up to 58* and I was at 1.022 down from 1.054 OG. That was last night. I left mine in the closet, took a reading this morning of 1.018, so I moveed it to a warmer area where it'll finish at 1.010 hopefully. If I was in your situation I would leave it because by the time you get the temp back down it'll be at the D-rest stage anyways...roll with it.

 

[Yooper]

i wouldn't cool it back down again as the yeast don't like swings in temperature.
i'd wait until its closer to the estimated fg and warm it by a few more degrees for the d-rest
as for the off flavours i believe most of them are created at the beginning of a ferment so you should be good.

I don't agree. Fermenting a lager above 55 degrees (or whatever the maximum optimum temperature is for that particularly strain) is never a good idea, unless you want an ale. Esters and other off-flavors will be created when the beer is fermenting at a too-high temperature. The diacetyl rest is done at the very tail end of fermentation, just to encourage the yeast to "clean up" any diacetyl. If the primary is cool enough and long enough, often a diacetyl rest isnt' even needed. More esters are created at the beginning, that's true- but at 1.036, it IS at the beginning. It's a long way until done. If you were at 1.020, that would be different.

 

[ChandlerBang]

I don't agree. Fermenting a lager above 55 degrees (or whatever the maximum optimum temperature is for that particularly strain) is never a good idea, unless you want an ale. Esters and other off-flavors will be created when the beer is fermenting at a too-high temperature. The diacetyl rest is done at the very tail end of fermentation, just to encourage the yeast to "clean up" any diacetyl. If the primary is cool enough and long enough, often a diacetyl rest isnt' even needed. More esters are created at the beginning, that's true- but at 1.036, it IS at the beginning. It's a long way until done. If you were at 1.020, that would be different.

Alright. I'm dumpin ice. Hopefully we don't get too many off flavors. I believe the yeast strain says a max temp of 58.

thanks

 

[Yooper]

Alright. I'm dumpin ice. Hopefully we don't get too many off flavors. I believe the yeast strain says a max temp of 58.

thanks

You can add a little at a time, to gradually bring it down. You don't want to go from 60 to 40 in a short period of time! Maybe one or two frozen water bottles in a water bath can do the trick.

 

[ChandlerBang]

You can add a little at a time, to gradually bring it down. You don't want to go from 60 to 40 in a short period of time! Maybe one or two frozen water bottles in a water bath can do the trick.

I tried that and it only came down a couple degrees. I have a lot of water because I wanted to protect it from a 5 ish or so degree daily temp swing. And up until yesterday the water in the swamp cooler had been stuck on 50-52 degrees. I assume the wort was actually 55 ish. I think I'll dump in the 7 pounds of ice and hope the weather cools off tonight like they are saying.
The yeast is Saflager 34/70? I'm going on memory here. It says it like the higher end of it's range 48-58. So I shot for 55.

The hydrometer sample tasted ok. Kinda sweet then kinda bitter.

 

[martinworswick]

More esters are created at the beginning, that's true- but at 1.036, it IS at the beginning. It's a long way until done. If you were at 1.020, that would be different.

maybe i have my info wrong but i thought that once you were over half way attenuated then the majority of the flavours had already been created? and that by cooling it down again you risk annoying the yeast into packing up their bags and going to sleep without finishing the job? or would that apply more to ale yeast?

not disagreeing,still learning,just asking