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Old 09-14-2012, 09:08 PM   #1
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Default Stuck fermentation help needed - Northern Brewer Imperial Stout

So I did Northern Brewer's Partial Mash Kit for Imperial Stout using Wyeast 1728 Scottish Ale. I made and stepped up a starter (twice) and should have had more than enough yeast to get through this bad boy.

Well I started with an OG of 1.086 which was right on target for what the recipe called for. That was on 9.7.12 at 1:30 am. I checked it on 9.11.12 and it was down to 1.032. I checked again just now (9.14.12) and the exact same thing 1.032. I see no visible signs of activity I know this doesn't mean much but the gravity staying the same worries me.

A couple things to note. The temperature of the fermenting beer is 67.5 degrees. It is recommended for this yeast to have a temp of 55-70. The first couple of days it was over 70 (74ish) so I put it in a swamp cooler and got it down to between 64-68. Would this drop in temperature after having a higher temperature mess with the yeast and cause it to slow down or stop? Secondly the attenuation for this yeast is 69-73% and based on my OG I should have a final gravity somewhere between 1.026, and 1.023. As it stands right now I have a ABV of 7.07. It should be higher.

So what should I do? Buy some more yeast, make a starter, and re-pitch? Any help would be greatly appreciated. Thanks

On a positive note - my bavarian hefeweizen, arrogant bastard clone, and dead ringer IPA are doing awesome with no problems whatsoever (as well as my blueberry wine and blueberry skeeter pee wine (I call it skeeter blood)

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Old 09-14-2012, 09:45 PM   #2
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A list of ingredients would help as then we can see what types and amounts of fermentables are there. If the grains were mashed too high you may have a less fermentable wort. In addition, it is possible the extract is less fermentable as well. It really depends.

Yes, depending on where the yeast was when you dropped the temperature, it may have shocked and dropped sooner than it should have. You can gently agitate the primary and try and rouse the yeast back into suspension and allow the temperature to self rise to ambient temperatures to try and help it along as well. I would do these things first before re-pitching. You can also taste your next sample to get a handle on how sweet it still is, it might possibly just be done.

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Old 09-15-2012, 01:57 AM   #3
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Originally Posted by duboman View Post
A list of ingredients would help as then we can see what types and amounts of fermentables are there. If the grains were mashed too high you may have a less fermentable wort. In addition, it is possible the extract is less fermentable as well. It really depends.

Yes, depending on where the yeast was when you dropped the temperature, it may have shocked and dropped sooner than it should have. You can gently agitate the primary and try and rouse the yeast back into suspension and allow the temperature to self rise to ambient temperatures to try and help it along as well. I would do these things first before re-pitching. You can also taste your next sample to get a handle on how sweet it still is, it might possibly just be done.
Duboman thanks for your help. Here are the ingredients:
Grain
.5 lbs English Roasted Barley
.5 lbs English Black Malt
.5 lbs English Chocolate Malt
Fermentables
12 lbs Dark Malt Syrup

I mashed 165 and less as it lost heat. Directions said to do at 170. I am going to leave it for tonight and maybe give it a gentle stir tomorrow. You are recommending taking it out of the swamp cooler? The temp will be about 69 degrees if I do that which shouldn't be a problem.

Using attenuation percentages I'm figuring the lowest gravity possible is 1.023 which would give me an alcohol percentage of 8.25. Right now I'm sitting at 7.07. I'm only low by 1.18 which isn't really that much. I was just hoping for around 9 or 9.5 for a nice warming alcohol note on a cold winter night but now that I'm running the numbers I guess this isn't possible. Also the taste is really good, not too sweet, just about perfect. I do think that it might be done fermenting. Thanks again for the response.
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Old 09-15-2012, 02:06 AM   #4
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>.I mashed 165 and less as it lost heat. Directions said to do at 170. I am going to leave it for tonight and maybe give it a gentle stir tomorrow. You are recommending taking it out of the swamp cooler? The temp will be about 69 degrees if I do that which shouldn't be a problem.

You mashed out at 165, or conducted the mash at 165?

If you mashed at 165, thats your problem, thats way too high

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Old 09-15-2012, 02:10 AM   #5
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>.I mashed 165 and less as it lost heat. Directions said to do at 170. I am going to leave it for tonight and maybe give it a gentle stir tomorrow. You are recommending taking it out of the swamp cooler? The temp will be about 69 degrees if I do that which shouldn't be a problem.

You mashed out at 165, or conducted the mash at 165?

If you mashed at 165, thats your problem, thats way too high
Well that's what it was when I put the grains in then it lost heat after I put them in. But I didn't think it was a problem since the directions said to do it at 170. Also aren't those grains being used for flavor and color and not for fermentables?

Edit: Could you explain the difference between mashing out and conducting the mash?
I'm not sure that these grains need to be mashed - more so steeped. But I'm not sure.. I'm new at this and lovin it!
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Old 09-15-2012, 02:24 AM   #6
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Quote:
Originally Posted by DaBills

Well that's what it was when I put the grains in then it lost heat after I put them in. But I didn't think it was a problem since the directions said to do it at 170. Also aren't those grains being used for flavor and color and not for fermentables?

Edit: Could you explain the difference between mashing out and conducting the mash?
I'm not sure that these grains need to be mashed - more so steeped. But I'm not sure.. I'm new at this and lovin it!
The malts you listed don't need to be mashed; so you're good with steeping them in the 170F-ish range - IMO that's not the root of your problem. More likely that the dark malt was less fermentable than the recipe anticipated.

Mashing is the conversion of starch to sugar by enzymes at a certain temp, and mashing out is done after the conversion is complete - it's adding a bunch of hot water to the mash to bring it up to about 170F to cease any enzymatic activity.
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Old 09-15-2012, 02:31 AM   #7
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The malts you listed don't need to be mashed; so you're good with steeping them in the 170F-ish range - IMO that's not the root of your problem. More likely that the dark malt was less fermentable than the recipe anticipated.

Mashing is the conversion of starch to sugar by enzymes at a certain temp, and mashing out is done after the conversion is complete - it's adding a bunch of hot water to the mash to bring it up to about 170F to cease any enzymatic activity.
I'm curious, so mashing out stops enzymatic activity that could potentially produce off flavors? How do you know when conversion is complete? Thanks for helping out I'm learning all I can so I can attempt AG.

So if the dark malt was less fermentable is there anything I can do? In hindsight what could I have done. Lowered the amount of dark malt and replaced it with a more fermentable malt? But then that would change flavor. Ugh. And how can you anticipate the fermantableness (yes it's a real word) of a specific malt?

The beer tastes good so I guess I shouldn't be discouraged but like I said I was just aiming for some higher alcohol for those cold winter nights.
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Old 09-15-2012, 02:37 AM   #8
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Try tossing in a champagne yeast and see if that'll drive the gravity down. It's possible your yeast aren't comfortable in the 8% range.

More likely though, is that the malt extract was higher in non-fermentables than the recipe expected. With only 1.5 lbs of steeped grains, and hitting your target gravity, it's unlikely the grains played a role.

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Old 09-15-2012, 02:42 AM   #9
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Try tossing in a champagne yeast and see if that'll drive the gravity down. It's possible your yeast aren't comfortable in the 8% range.

More likely though, is that the malt extract was higher in non-fermentables than the recipe expected. With only 1.5 lbs of steeped grains, and hitting your target gravity, it's unlikely the grains played a role.
Do you think that would adversely affect the flavors of an already tasty beer? Don't get me wrong I do want more alcohol but not if it will ruin the flavor. Thanks for input.
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Old 09-15-2012, 02:54 AM   #10
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Do you think that would adversely affect the flavors of an already tasty beer? Don't get me wrong I do want more alcohol but not if it will ruin the flavor. Thanks for input.
It shouldn't. The champagne yeast won't have all that much to eat, if anything, and won't impact the flavor noticeably. Had you used only champagne yeast, yeah, it'd be much drier. Also, it will ensure you have live yeast for bottling.

The champagne yeast advice was given to me by a brewer at Sun King in Indy, so I trust his judgment.
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