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Old 03-02-2010, 09:03 PM   #1
hector
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Default Low Attenuation

Hi there !

According to Palmer's "How To Brew" , the apparent attenuation of a yeast strain depends on

the types of sugars in the wort that the yeast is fermenting .

Does a low attenuation mean that the wort consists mostly of unfermentable sugars ?!

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Old 03-02-2010, 09:15 PM   #2
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Yes and no, but mostly yes. Each yeast strain has it's own attenuation properties. If you split a batch between Nottingham and Windsor yeasts, the Nottingham would attenuate much better. So, it's really all about working with the expected attenuation range for any given yeast.

That being said and from what I've seen, and primarily on all-grain batches, 9 times out of 10 low attenuation is usually due to wort fermentabililty. In most cases, it's caused by mash temp being high... unexpected or otherwise.

Other things can have an affect as well... like yeast pitch rate and viability, aeration or lack thereof, water mineral composition, etc. But the biggest impact on attenuation is the wort composition in regards to fermentable and unfermentable sugars.


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Old 03-02-2010, 09:34 PM   #3
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So , if it's mostly because of the type of sugars , would the attenuation increase if

I would use much more of the same malt extract ?!
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Old 03-02-2010, 09:44 PM   #4
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With malt extract you don't have control of the proportions of fermentable and unfermentable sugars - that's determined when the extract is made (by the company who produces the extract from a temperature controlled mash then subsequent spray-drying to concentrate the wort to make "extract").
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Old 03-02-2010, 10:33 PM   #5
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Quote:
Originally Posted by Frodo View Post
With malt extract you don't have control of the proportions of fermentable and unfermentable sugars - that's determined when the extract is made (by the company who produces the extract from a temperature controlled mash then subsequent spray-drying to concentrate the wort to make "extract").
So , what should I do with the malt extract and yeast which lead to a low attenuation , as I have no other choice ?!

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Old 03-02-2010, 11:47 PM   #6
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Not much you can do, if you can't change the yeast.

What are you calling low attenuation?
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Old 03-03-2010, 11:19 AM   #7
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Quote:
Originally Posted by david_42 View Post
Not much you can do, if you can't change the yeast.

What are you calling low attenuation?
Apparent Attenuation = 59%

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Old 03-03-2010, 03:25 PM   #8
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59% is low, about what I'd expect from Muntons yeast in an all-extract recipe. You could add some sucrose or dextrose. That will raise the ABV and reduce the impact of the unfermentables. In future recipes, if you have to use the same extract and yeast, substitute sugar for 15-20% of the extract.
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Old 03-03-2010, 05:03 PM   #9
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I'm guessing it's either the number of yeast you're pitching, or the fermentation temperature (though I'm no expert by any means).

Not sure if you're doing it already, but a sizable yeast starter (for liquid yeast) or more packets of dry yeast (rehydrate them prior to pitching) will help get a higher attenuation closer to what the yeast is rated at. There's a good discussion on how much yeast you should pitch in How to Brew. Without the appropriate number of yeast you might not get to the expected attenuation, and you can get off flavors.
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Old 03-03-2010, 07:04 PM   #10
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Quote:
Originally Posted by Frodo View Post
I'm guessing it's either the number of yeast you're pitching, or the fermentation temperature (though I'm no expert by any means).

Not sure if you're doing it already, but a sizable yeast starter (for liquid yeast) or more packets of dry yeast (rehydrate them prior to pitching) will help get a higher attenuation closer to what the yeast is rated at. There's a good discussion on how much yeast you should pitch in How to Brew. Without the appropriate number of yeast you might not get to the expected attenuation, and you can get off flavors.
I used dry yeast and determined the pitching rate by using the calculator in "www.mrmalty.com" .

Should I pitch more yeast than what the calculator says ?!

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