attenuation, pt II

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KayaBrew

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What would cause a yeast to not fully attenuate? I have an IPA with an OG of 1.061 and after 2 weeks I am (only) down to 1.019, giving my yeast an attenuation of only 69%. It has been fermenting at 64-67F. I am using WL051 from a 2 liter starter. The White Labs site states this yeast should attenuate to 70-75%. I want to squeeze more ABV out of this beer. Is 68% good enough, or am I obsessing? Could I raise the temp. to say 70 or 72?
 

boo boo

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Under pitching is the main cause. Other causes are too low a fermenting temp for the yeast, low oxygen levels, lack of actual fermantable sugar, and bad yeast to name a few.
 

Yambor44

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Raise the temp to 70 and let it go 4-5 days then check the gravity again. It should finish out at your OG divided by four which in this case would be about 1.015 (61/4=15.25)
 

ScottD13

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You should be aware that the attenuation ranges given for any yeast are a range based on average wort fermentability, but what’s in an average wort?

There are many, many factors that can affect (or is it effect) attenuation and yeast is only half of the equation. Wort fermentability plays just as important a part in attenuation as yeast does. For example, different mash temps can change the sugar content of any given wort if you’re all grain, and different extracts have different fermentability levels depending on manufacturer.

By manipulating your wort you can use a less attenuative yeast and ferment the snot out of beer just by adjusting the mash temp or using enzymes to break up the unfermentable sugars.

Now, as boo boo pointed out, you not only have to take into account the fermentability of your wort you have to pitch the right about of healthy yeast to achieve the attenuation you want. It can be a very overwhelming concept to grasp, I’ve been consistently brewing for 18 months but have actually been brewing on and off for 10 years, with an 8 year hiatus, and only do I now have a good understanding of attenuation.

Here’s a few resources that may help you

www.mrmalty.com - check out the Pitching Rate Calculator
How to Brew - By John Palmer - Yeast - John Palmer’s Online Chapter on Yeast
The Brewing Network.com - Brew Strong: Brew Strong: 08-18-08 Attenuation check out this pod cast as well. Excellent advise!
 
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KayaBrew

KayaBrew

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Thanks to everyone. Lots of good info here. I'm not content with just brewing good beer, I want to brew great beer and I want to understand why certain things are or are not happening in my brews.
 

Bob

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Post your complete recipe, including ingredient brand and source, if known - for example, "6.6 lbs Muntons Amber LME (UK)". Lots of us here have broad knowledge about single ingredients and their impact on other things in the brew. Maybe we can look at your recipe and give some advice/troubleshooting.

As Scott pointed out, there are myriad factors that impact attenuation. Ingredients not yeast can be quite important!

Cheers,

Bob
 
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KayaBrew

KayaBrew

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Here's the recipe

AHS American IPA-I

.5 lb 2-row
.25lb Special B
1 lb Crystal 60L
Steeped for 25 min. @ 160F
8lb AHS X-Pale LME
added +/- 4lb at beginning of boil, +/-4lb at 45 min. into boil
1oz Columbus bittering boil for 60 min.
1oz Cascade flavoring boil for 15 min.
1oz Cascade aroma boil for 5 min.
White Labs California Ale V 051 started in 2 liters 1.041
pitched when wort was at 75F, yeast was at 72-75F

do you need any other info? As stated before, this was fermented at an average temp. of 65F (+/- 2 degrees)
It's been 14 days since I pitched the yeast.
Thanks!!
 

Bob

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Huh. Cal V should go to town on the simple sugars present in those ingredients. Here are my thoughts:

You conducted your ferment just outside the low end of the preferred temperature range. Combine that with the stated average attenuations, and you should have calculated a complete lack of surprise. It's the law of averages: if you ferment low, you'll get low attenuation. 65degF = <70% attenuation.

WLP051 is a bit more labor-intensive than WLP001 or W1056. Let me quote some feedback from the White Labs web page for WLP051:

I find that it does need some rousing to completely attenuate[.]
The WLP051 is a bit slower than other strains, which is one reason for its clean profile. It is also more temperature sensitive, so it might have slowed down more due to the temperature. I would rouse again, and raise the temperature to 72, there's no need to keep it low now because it is not fermenting quickly.
There's your solution: put the fermenter in a warmer place and gently rock it a few times to get the yeast back into suspension. White Labs recommends racking the beer to rouse, but that doesn't make sense to me; if you take the beer off the yeast bed, how can you possibly rouse it?

Anyway, warm it and rouse the yeast. That's my advice.

Bob
 
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KayaBrew

KayaBrew

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Thanks, Bob. Very helpful.
 

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