Diacetyl rest in a Pils: before or after racking?

[Duchifat]

Dear fellow brewers,
I am brewing a Pilsner style beer. I am nearly 3 w into fermentation at 14C, using Saflager W-34/70. Although nearly all online sources recommend a diacetyl rest for this style, I could not find an unambiguous answer to the question: should this be done in the fermentor, or should I first rack the beer, then perform the rest? Maybe there is no good reason to make a fuss about this?
After the diacetyl rest, my plan is to lager in kegs at 2C for 3-4 w.
TIA,
Michael

 

[Minbari]

Has to be in the fermenter. you want to off gas the diacytl before you keg it or bottle it

 

[Duchifat]

Has to be in the fermenter. you want to off gas the diacytl before you keg it or bottle it

Minibari, thank you for your fast reply.
Diacetyl is in fluid form. To my understanding, the way we try to get rid of it is by allowing re-uptake in the yeast cells, where it is then metabolized to products that do not affect the taste of the beer; It is not just gassed off. So, in principle, I could keg (say without CO2), let it rest for a day or two at 20C, and then lager. But maybe then I would be letting too much yeast behind in my fermentor to allow the process to run efficiently?
Michael

 

[Josh Hughes]

Unless you are filtering you will have plenty of yeast. The diacetyl will metabolize with time but a rest before racking is quicker. Traditional German breweries don’t do one. They rack with a plato left and let it lager. I have kegged with 4 gravity points left, let it sit a day like that and then put in the refrigerator with no issues.

 

[Josh Hughes]

Also great to see you post on the forum. You’ve been at it a while. Im always look to learn

 

[Sandy Feet]

I did a bunch of research online and spoke to an assistant brewer that got paid for brewing for about 30 minutes at a bar one night. It was my understanding (and it worked for me) that the D rest should be done at low krausen in the fermenter. I pitched the living shit out of the 34/70 when I used it, so my low krausen was about Day 3 or Day 4. My beers noticeably took off within 18-24 hours. My first beer had a very slight sulphur smell before kegging, but nothing crazy. The other 2 had zero sulphur smell at the time of kegging. You want to do the rest while the yeast is still somewhat active.
I think the thing that surprised me the most is that fermentation, at least with 34/70 pitched heavy, is about the same as an ale. The difference is the time it takes to get the crispness that you want from a lager. That is where the additional few weeks come in.

 

[HighVoltageMan!]

The yeast have to be metabolically active (fermenting) to reduce the VDK/diacetyl compounds. The problem lies in where it forms. It can form after the yeast have dropped out by oxidizing the VDK compounds. If your beer has been in the fermenter for 3 weeks, I think it's done. You should have hit your final gravity by now. If not you have other problems.

I think at 14C for 3 weeks, the likelihood of diacetyl in beer is low. If you had a healthy fermentation you likely have little to worry about. I ferment 34/70 at 9-10C for 7 days and raise it slightly to no more than 13C and let it finish. I rarely let the beer go more than 14 days before I crash cool it to 0C.

The D-rest isn't always necessary and some brewers skip it and rely on a robust fermentation. I just use ALDC enzyme at pitch and forget about it.

 

[Minbari]

Minibari, thank you for your fast reply.
Diacetyl is in fluid form. To my understanding, the way we try to get rid of it is by allowing re-uptake in the yeast cells, where it is then metabolized to products that do not affect the taste of the beer; It is not just gassed off. So, in principle, I could keg (say without CO2), let it rest for a day or two at 20C, and then lager. But maybe then I would be letting too much yeast behind in my fermentor to allow the process to run efficiently?
Michael

You are correct, not sure what I was thinking. But, I would still do it in the fermenter. I anyways do it just before active fermentation is finished. Never had an Issue with it

 

[dmtaylor]

Yeast eats diacetyl. You should perform a diacetyl rest before racking. If you do it after racking, there is still yeast present so it will still work, but might (at least in theory) take longer.

 

[Duchifat]

Josh, Sandy Feet, HighVoltageMan, Minbari and Dave, thank you all for your helpful comments. Summing up, fermentation went pretty well, so I'll give the batch a critical taste and then decide whether or not to give it a rest before lagering. Thanks!

 

[Steve Ruch]

First thing you should do is determine whether you actually have diacetyl and actually need a d-rest.
I've never detected any with this yeast.