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 ?!

Hector

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.

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 ?!

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").

Frodo said:

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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So , what should I do with the malt extract and yeast which lead to a low attenuation , as I have no other choice ?!

Hector

Not much you can do, if you can't change the yeast.

What are you calling low attenuation?

david_42 said:

Not much you can do, if you can't change the yeast.

What are you calling low attenuation?

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Apparent Attenuation = 59%

Hector

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.

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.

Frodo said:

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.

Click to expand...

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 ?!

Hector

We've reached the limit of my knowledge... Not too hard to do really.

I see that this is a super old thread, but I have been doing a MASSIVE amount of research and testing as of late because I too suffer from chronic low attenuation (CLA).
Mr Malty is a good calculator, but I find it comes up with drastically different cell counts than the calculator on Wyeast's website. I tend to error on the safe side so I use the wyeast website because I do two step starters on a stir plate. (2 liter for 24 hours then add 3L for 5L total volume for another 24 hours). chill, decant, pitch.

Because I brew all grain I have started doing forced ferment/forced attenuation tests on each batch. I harvest 200 ml of wort 12-24 hours into fermentation and put it on my stir plate in a warm location (greater than 72 degf) after 24 hours of continous aeration on the plate I take a gravity, thus giving me the highest possible attenuation that I can expect from that batch. If I have low attenuation from that test then I know that my problems exist on the hot side of the brewery and I need to start looking at conversion, mash temp and grain quality. I found this test in the "testing" section of Mr Malty/Jamil's book "yeast: a practical guide to beer fermentation"