How do you decide when it's time to D-rest your lager?

[Tippsy-Turvy]

Simple question particularly given the theory is well known ie "75% of the projected attenuation". However, given quite a few lager brewers (on this forum and others) don't seem to reach their targeted FG, what do you do in practical terms?

If the achieved FG is going to be higher than projected then waiting for the original 75% target could mean that the fermentation is 80-90% done already. If the FG ends up being lower than projected then the D-rest might begin way too early.

For my case, I was plotting the SG readings for my current first lager attempt and, by crudely extrapolating the current trajectory, it seems like my forecast FG might not be reached. So, if the new projected FG is accurate, I should actually start the D-rest now. Waiting for the original 75% target SG would mean ~83% fermentation, based on the new projection.

What do you guys do? Does it even matter that much whether it's 65% or 85%?

FYI, the red line is the original target 75% fermentation level and the red dot is the original FG estimate (which i assumed would be achieved by 21 days)

 

[fantomlord]

I don't think it's important to start your D rest at exactly 75% of your total attenuation. I believe the important part is to start it when you still have active fermentation. So, if you start it once you've hit about 75% of your expected total attenuation, you should be fine. I've done this with all of my lagers, and haven't had a diacetyl issue yet. YMMV

 

[beersk]

I let the fermentation temperature raise naturally to the mid 60's after about a week in the fermenter. Let it roll for a week, then keg. Simple. Do it.

 

[Tippsy-Turvy]

You know, what you guys say make a lot of sense. So long as the bulk of the fermentation is done at the lower temps then surely ester production is essentially controlled. Then, it won't matter whether there's 15% or 30% fermentation remaining so long as there's a reasonable amount of active yeast to do their thing with any diacetyl (helped by a higher temperature, of course).

If true, then in future I won't need to even open my fermenter repeatedly and run the risk of infecting my "precious". I could simply time my d-rest by following a fixed schedule, eg a week, or just watch for the activity to die down or a blend of the two.

Unfortunately, i might have already infected this batch (see pic below) since those floaties weren't there before. I've had a string of problems with my brewing lately and frankly i'm losing confidence, but this is an entirely different subject.

Anyway, you guys have given me great ideas on how to time my future d-rests and without the risk of infecting my beer. Many thanks!

 

[Yesfan]

..........Unfortunately, i might have already infected this batch (see pic below) since those floaties weren't there before. I've had a string of problems with my brewing lately and frankly i'm losing confidence, but this is an entirely different subject........

That looks like normal yeast rafts to me. I've had a few batches look like that, and everything looked normal.

 

[m1k3]

I D-rest all my beers (ales or lager).

In my opinion, it's a good practice to let them free rise up to the max recommended fermentation for the yeast for a few days at the end.

I don't take hydrometer readings but have a pretty good idea visually when it is time.

 

[passedpawn]

View attachment 290233

Where'd you get that red line from? Looks like it's at about 1.017, and the OG looks to be about 1.045.

I'd say that 75% attenuation should be about 1.012, or about where your extrapolation ended up after 3 weeks.

I make pilsners fairly often (drinking one now . OG ~ 1.048. Ferment at 50F for 2 weeks. At that point they are usually around 1.018.

I raise the temps to 65 and a week later they are 1.010.

At that point I add gelatin and crash to 33F.

 

[Tippsy-Turvy]

That looks like normal yeast rafts to me. I've had a few batches look like that, and everything looked normal.

Pal, that's music to my ears!

I don't take hydrometer readings but have a pretty good idea visually when it is time.

It seems like all you guys rely on rules-of-thumb and not regular SG readings, no doubt because you've all had so much experience brewing lagers. What are the visual signs you look for?

I recall for this batch at peak activity there was still no krausen but there was the constant streaming of bubbles rising plus the wort/beer had become cloudy with suspended yeast. So, I'm guessing that once the yeast settles into a cake again and the bubbles have died down to just a trickle (plus assuming it's been about a week) that that might be a reasonable time to d-rest or at least take the first gravity reading?

I'd say that 75% attenuation should be about 1.012, or about where your extrapolation ended up after 3 weeks.

Oops, perhaps I've misunderstood the calculations. I thought the "75%" applies to the attenuation range ie if OG is 1.047 and FG is estimated to be 1.007 then the "75%" would be 0.75*(47-7) =30 so the target SG would be 1.047-1.030 = 1.017?

Well, it's been in a d-rest for 2 days now and the SG was probably ~1.020 at the time. Darn.

 

[passedpawn]

Oops, perhaps I've misunderstood the calculations. I thought the "75%" applies to the attenuation range ie if OG is 1.047 and FG is estimated to be 1.007 then the "75%" would be 0.75*(47-7) =30 so the target SG would be 1.047-1.030 = 1.017?

Well, it's been in a d-rest for 2 days now and the SG was probably ~1.020 at the time. Darn.

Wrongo. In your example, FG should end up around 1.012. Hey, they said there wouldn't be any math in this course!

 

[Iseneye]

Where did you get your estimated FG number from? Seems low to me.

If you want to know what your FG will be you can do a forced ferment test with your wort and yeast.

Once you've done a couple of lagers there is no real need to take a reading every day.

 

[Gavin C]

Just to give you an idea from one new lager brewer to another.

Here are a couple of links to some great lager brewing info. I've learned a great deal from these both in practical and theoretical applications.

http://brulosophy.com/methods/lager-method/

http://braukaiser.com/wiki/index.php?title=Fermenting_Lagers

Here are some visuals of a recent lager ferment with associated gravities. It may be useful to you in determining when and if to measure gravity. Although a hybrid profile was used for the ferment I recently rebrewed this with WLP833 at more usual lager temperatures with similar visuals but a longer time frame.

Fermentation with WLP833 (2 weeks to kegging and currently lagering at 35F)

OG 1.048 FG 1.010 A Munich Helles

OG 1.048


20 hours post pitch fermenting at 55F (hybrid yeast used WLP029)

50 hours post pitch at which point a passive rise to 68F was started


Final Gravity



All measures were taken at 68F (this particular hydrometer's calibration temp)

 

[Tippsy-Turvy]

Wrongo. In your example, FG should end up around 1.012. Hey, they said there wouldn't be any math in this course!

Sorry Andrew, but I'm still not getting it! Must be too much homebrew.. Perhaps we're referring to different things?

If we're referring to the time to start a d-rest, shouldn't it be "75% of the way towards the FG"? So, if the OG is 1.047 and FG is 1.007 then 75% of the way there would be 0.75*(1.047-1.007) = 1.017?

If we're talking about 75% apparent attenuation, then I can see where the 1.012 comes from (0.75*1.047 = 1.012) otherwise I'm not sure how to get that number.

Now i have an excuse for another beer

 

[Tippsy-Turvy]

Sorry guys, was writing my reply when your posts came in.

My FG was determined on Brewer's Friend. I pitched W-34/75 (after I destroyed my WLP830 starter) which, according to BF, has an AA of 83%. Also, I mashed low at 147F.

Wow, Gavin. That's pretty detailed record keeping you have there! Are you an auditor?

It seems you began your d-rest at 1.020 (or 75% of the way towards FG) which makes sense. But firstly, I'm impressed by the size of that krausen (I had barely anything). Then, I'm shocked that you reached your d-rest gravity level in just 50 hours! Your initial fermentation temp is marginally warmer than mine (49F) but still, that's impressive yeast health you're displaying there. How did you decide it was time to test the gravity for the d-rest? I'm guessing that the krausen had fallen quite noticeably.

Oh yes, many thanks for the links. More tricks for an old dog to learn.

 

[Gavin C]

...

Wow, Gavin. That's pretty detailed record keeping you have there! Are you an auditor?

Thanks for the compliments Tipsy. Not an auditor, but I do enjoy documenting the process. I'm a total geek who's found, in homebrewing, an enjoyable outlet for my tendency to (over-)analyze things.

..
It seems you began your d-rest at 1.020 (or 75% of the way towards FG) which makes sense..... How did you decide it was time to test the gravity for the d-rest? I'm guessing that the krausen had fallen quite noticeably.

The ferment was pretty fast I guess as the images are from the brew with WLP029 fermented at near lager temperatures. When I used WLP833, OG was again 1.048, D-rest point was at 5 days post pitch at an SG of 1.014 and FG was verified at 1.009 11 days post pitch.

48 hours after pitching, fermentation was ticking away with this lager. The krausen dropping seemed to be a reasonable point to check the gravity.

48hours after pitching WLP833 at 48F and fermenting at 50F


I was a little further on in the fermentation on that one when I started the passive rise to 68F, trying to follow the Braukaiser's more traditional approach rather than Brulosopher's fast lager method. FG on the WLP833 was 1.009

Lager brewing and its fermentation methods certainly adds another layer of
interest for me. Tons of fun.

 

[passedpawn]

Sorry Andrew, but I'm still not getting it! Must be too much homebrew.. Perhaps we're referring to different things?

If we're referring to the time to start a d-rest, shouldn't it be "75% of the way towards the FG"? So, if the OG is 1.047 and FG is 1.007 then 75% of the way there would be 0.75*(1.047-1.007) = 1.017?

If we're talking about 75% apparent attenuation, then I can see where the 1.012 comes from (0.75*1.047 = 1.012) otherwise I'm not sure how to get that number.

Now i have an excuse for another beer

The fault is mine here. I haven't been paying attention to your thread title. I see what you're saying there. You drew the red line at 75% of your expected attenuation. So, OK, that's pretty neat what you're trying to achieve there.

I don't do it by SG, although that is certainly the best way. However, I've been doing this long enough that I know what to expect without measuring the gravity often. I put my schedule above.

So, if my OG was 1.048 and FG was 1.010, my attenuation was about 80%.
If I started my D-rest at 1.020, then I guess (in your terms) I started my D-rest at about 74% of expected attenuation Interesting!

 

[m1k3]

It seems like all you guys rely on rules-of-thumb and not regular SG readings, no doubt because you've all had so much experience brewing lagers. What are the visual signs you look for?

I'd hate to have to ferment in opaque plastic or stainless since I really rely on watching the fermentation. When I started I didn't want to risk infection taking samples. (I'm sure many people can do it in a sanitary way but it was never my process.)

My preferred buckets are semi-transparent so I can see the krausen when fermentation starts and when the wort goes from a darker color to a milky white and when there is folcculated yeast accumulating on the bottom, and when the beer drops bright.

When I see ANY folcculated yeast accumulating on the bottom of the fermenter I know that I should be ramping up to the D-rest (as high as the maximum recommended ferm temp for the strain).

I've done 47 all grain batches (only four were lagers), I can make 1F temp adjustments daily to keep the fermentaton rising all the way from the minimum suggested ferm temp to the max and then I hold it for a few days as I watch for further floculation until I feel it's ready to cold crash.

 

[Tippsy-Turvy]

When I see ANY folcculated yeast accumulating on the bottom of the fermenter I know that I should be ramping up to the D-rest

That's a great rule of thumb and exactly what i'll incorporate into my d-rest guideline. Many thanks.

Funny. I've been eyeing a 20L Speidel fermenter for almost a year now and it's the same reason holding me back everytime - I won't be able to watch the activity! I guess speidel owners have to time their d-rests by fixed time schedules or regular gravity readings.

 

[wobdee]

That's a great rule of thumb and exactly what i'll incorporate into my d-rest guideline. Many thanks.

Funny. I've been eyeing a 20L Speidel fermenter for almost a year now and it's the same reason holding me back everytime - I won't be able to watch the activity! I guess speidel owners have to time their d-rests by fixed time schedules or regular gravity readings.

The Speidel's are clear enough that you can tell when the yeast cake starts to form. You can also unscrew the top and look for the krausening to fall.

 

[Tippsy-Turvy]

The Speidel's are clear enough that you can tell when the yeast cake starts to form

You serious? From the pictures the plastic just looks thick and fully opaque. I even thought about drilling a hole near the top and gluing a piece of PVC on it to form a "spy hole"!

Ok, I guess Christmas is not too far away..