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Old 09-02-2013, 09:25 PM   #1
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Default Lager help...

I've got an Oktoberfest and a doppelbock fermenting. The OG for O-fest was 1.062 (hoping to hit 1.016 or better), while the doppelbock was 1.090 (aiming for about 1.020). Did my best to pitch "mighty starters" on each (1.7L for the O-fest; 5L for the doppelbock). Fermented each in 48-52 degrees for about 10 days. Checked the gravity and both were about 80% to 85% done (1.023 for the O-fest and 1.032 for the doppelbock.

At that point, I bumped the temp to 65-67 for a d-rest and it's been there for about 3 days now.

I just transferred to kegs to start the lagering process, but as near as I can tell the gravity didn't drop during the d-rest. Now I'm concerned that the beers aren't going to attenuate fully.

The samples didn't seem wort-y sweet (well, maybe a touch sweet for the o-fest but not overwhelmingly so).

Will the beers finish up during lagering? At lagering temps and being off the yeast cake, I have difficulty believing that the yeast will not go dormant. I know it's not necessary to drop the temps in steps to get down to ~32, but would it be beneficial in this case so as to keep the yeast a big more active while the temps drop?



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Old 09-02-2013, 10:45 PM   #2
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At lagering temperatures, the yeast will be dormant. If they aren't done, keep them at fermentation temperatures or above until they are done. The SG will not go lower during lagering, and much of the yeast will drop out as the beer clears.

Are you sure of the SGs? They seem terribly high for a beer that doesn't taste sweet. If you used a refractometer to check, run and check with a hydrometer.



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Old 09-02-2013, 10:55 PM   #3
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I checked with a hydrometer. The only things I can think of that might have happened are that a) in pulling the fermenters out of the freezer, they were shaken up a bit, which probably released a lot of trapped CO2 that may have futzed with the reading and/or b) the temp was starting to come up as I was transferring, which also affected the reading.

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Old 09-02-2013, 11:09 PM   #4
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Originally Posted by mclamb6 View Post
I've got an Oktoberfest and a doppelbock fermenting. The OG for O-fest was 1.062 (hoping to hit 1.016 or better), while the doppelbock was 1.090 (aiming for about 1.020). Did my best to pitch "mighty starters" on each (1.7L for the O-fest; 5L for the doppelbock). Fermented each in 48-52 degrees for about 10 days. Checked the gravity and both were about 80% to 85% done (1.023 for the O-fest and 1.032 for the doppelbock.
80 - 85% apparent attenuation is more than enough but you didn't get anything like that. For the doppelbock: (90 - 32)/90 = 64% and for the O'fest (62 - 23)/62 = 63%.

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At that point, I bumped the temp to 65-67 for a d-rest and it's been there for about 3 days now.

I just transferred to kegs to start the lagering process, but as near as I can tell the gravity didn't drop during the d-rest.
If there was no change in during a diacetyl rest at elevated temperature that is a pretty good indication that the fermentation is finished.

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Now I'm concerned that the beers aren't going to attenuate fully.
Assuming that the AE readings are correct (using a refractometer would indeed give you erroneously high readings and, as you are reporting in SG units you should also be aware that the SG values on some refractometers are not correctly converted from the Brix) you are pretty much stuck where you are. You didn't use White Labs Oktoberfest strain by any chance did you? If you did therein lies the explanation. That stuff just won't ferment more than about 55 - 60%. If another strain was used then the possibilities include inadequate oxygenation and insufficient pitching.

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Will the beers finish up during lagering?
Most probably there will be no further attenuation. With a healthy ferment in which conditioning is begun at perhaps 1.5 °P above terminal the beer may creep down another 0.1 or 0.2 during the months of lagering if lagered on the yeast.

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At lagering temps and being off the yeast cake, I have difficulty believing that the yeast will not go dormant.
They do for the most part but that's one of the secrets of home brew lager. They don't entirely. If stored on the yeast cake their minimal activity can keep the beer fresh for well over a year and drinkable up to 2 yrs and a bit more sometimes.


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I know it's not necessary to drop the temps in steps to get down to ~32, but would it be beneficial in this case so as to keep the yeast a big more active while the temps drop?
Theoretically if you do a diacetyl rest yoy can crash the beer because the yeast have done the entire cleanup during the rest. But one of the reasons that the traditional method (no diacetyl rest, gradual cooling, lagering on the yeast) makes better beer (besides better head retention) is the effect I mentioned above.
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Old 09-03-2013, 12:45 AM   #5
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That's not how you would calculate the percentage completion is it? Wouldn't you take the difference between the OG and the point I measured the gravity divided by the delta between the OG and the target FG--i.e. (1.090 - 1.033)/(1.090 - 1.020) = .57/.070 = 81%?

The yeasts used were WLP838 (O-fest) and WLP833 (Doppel).

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Old 09-03-2013, 01:37 AM   #6
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Brief addendum: decided to check my hydrometer for accuracy. It reads .004 too high. That helps explain a few things and if I can squeeze a few more points out of each, I'll at least be within style guidelines. I'm going to leave the temp at around 62 for a few days and hope the yeast in suspension will dry it out a bit more before I drop the temp for lagering.

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Old 09-03-2013, 03:38 AM   #7
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That's not how you would calculate the percentage completion is it? Wouldn't you take the difference between the OG and the point I measured the gravity divided by the delta between the OG and the target FG--i.e. (1.090 - 1.033)/(1.090 - 1.020) = .57/.070 = 81%?

The yeasts used were WLP838 (O-fest) and WLP833 (Doppel).
If you look up WLP838 on White Labs wesite you will find that it is listed as having an attenuation of 68 - 76%. Attenuation (apparent) is defined as

Apparent Attenuation = 100*(OE - AE)/OE

where Original Extract and Apparent Extract are both in °P but you can use points without introducing as much error as is incurred due to hydrometer inaccuracy (esp. in your case where your hydrometer is off by about 1 °P). Putting your numbers for the O'fest into this formula you have realized 63% attenuation. That is below the lower expected limit by 3% but still indicative of a weak fermentation.

For the 833 the numbers are 70 - 76% (that's more typical). In your definition you have decided that 100% complete means an AE of 20 points corresponding to an apparent attenuation of 78%. How did you arrive at that number? It is more than this yeast is expected to be able to do. You are, of course, free to come up with any metric you want but it seems to make most sense to use the standard apparent attenuation so you can compare to the manufacturer's data. Again, in the case of the doppelbock, you have realized less than the expected minimum attenuation (64%) also indicating a weak fermentation.
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Old 09-03-2013, 04:15 AM   #8
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If the goal is to start the d-rest when the fermentation is at least 75% complete, then unless I'm missing something, I'm not concerned about "total" apparent attenuation. In other words, I want a percentage of a percentage (75% of 75% (as an example) apparent attenuation). I'm not trying to be a d!ck, I want to understand. My reading as always been that you do a d-rest once you are 75% of the way (or better) to the target final gravity. You are calculating the total apparent attenuation. This might be the correct calculation, but it's never been how I read the description of when to start a d-rest.

I guess a second way of describing it is that your method suggests a d-rest when the beer is essentially done fermenting. That's just never been my understanding.

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Old 09-03-2013, 04:30 AM   #9
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As for picking 1.020, I was simply going for a nice mid point in the style that would give me malty, but not particularly sweet. I know I was pushing the bounds of the yeast's typical performance but thought I might get there with a big starter and a pretty fresh vial.

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Old 09-03-2013, 05:01 AM   #10
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If the goal is to start the d-rest when the fermentation is at least 75% complete,
I've never heard it stated that way. It is usually asserted that one starts the diacetyl rest or temperature glide when there are 1.5 to 2 ° of extract remaining i.e. when the AE is 1.5 - 2 ° (6 - 8 points) above the expected terminal AE. But how does one know what terminal is? One way to determine when you are a couple of degrees above terminal is to do a forced fermentation test in which you remove 100 mL if fermenting beer and put it in a hydrometer test jar which you remove to a warm place. This will ferment out faster than the colder wort in the main fermenter. You then measure the AE of that and assume that the beer will eventually come to that AE and start your glide or diacetyl rest when the AE of the beer is a couple of degrees above the test AE. A more experienced brewer has brewed the beer in question or one very similar to it many times before and knows by other signs such as gas evolution rate when it is time to start temp. down. I my brewing, for example, when gas evolution slows I spund the fermenter and then monitor gas pressure. When it stops rising it is time to start the temperature down (I don't do diacetyl rests - the gradual cooling produces a better, more stable beer).


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then unless I'm missing something, I'm not concerned about "total" apparent attenuation.
I think you are. In the examples you gave it is analysis of the AE that lets us detect that you are experiencing weak fermentations for some reason.
.

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I guess a second way of describing it is that your method suggests a d-rest when the beer is essentially done fermenting. That's just never been my understanding.
As noted above I don't suggest diacetyl rests. That method was developed by commercial brewers who are looking for a quick way to get the beer off the loading dock. The traditional methods of cool fermentation followed by a gradual decrease in temperature to near freezing and long lagering make, IMO, better beer (with no diacetyl beyond the threshold amount which is an important part of Bohemian Pilsner).

But in any case I am not suggesting that the temperature glide, or diacetyl rest be done when the beer is finished fermenting. I am suggesting that they commence when the AE is within 2 ° of terminal. I was not, in the previous posts, trying to tell you when to start your diacetyl rest but rather using AE to diagnose your fermentation problem.

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As for picking 1.020, I was simply going for a nice mid point in the style that would give me malty, but not particularly sweet. I know I was pushing the bounds of the yeast's typical performance but thought I might get there with a big starter and a pretty fresh vial.
Your approach has been to assume that you will get
20 points from a 90 point wort when the manufacturers specs tell you will get between 22 and 27. This is not a good assumption on which to base your decision to start a diacetyl rest because you do not know that you are going to get 20 - in fact it is very unlikely as you have seen. You, in fact, got less attenuation at 33 than the lower expected limit. A more reasonable approach would be to take the midrange specified by the manufacturer which would give you 25 points and plan your rest for 2 ° above that or 33 which is what you wound up doing but it did not work for you because your attenuation was not even as much as the manufacturers specified minimum. You must fix your fermentation problem.

A forced fermentation sample or monitoring of the gas evolution or plotting of the AE on a daily basis would have indicated to you that you weren't getting the attenuation you should. You might then have taken action such as repitching more yeast or adding vigorously fermenting wort (krausening). That might save these beers at this point and will certainly remove any diacetyl.


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