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Old 05-22-2012, 05:48 PM   #1
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Default Getting 84% Apparent Attenuation with US-05? Why so high?

So since I have switched to AG my Apparent (Measured) Attenuation has gone up significantly. When I did partial mash I was getting 75%. Now that I'm AG I'm getting 83-85%.

For example my last batch (brown ale):

OG @ 65F = 1.051
FG @ 65F = 1.008

According to this calculator: http://pint.com.au/calculators/alcohol/
My Apparent attenuation is 84% whereas US-05 yeast is only supposed to attenuate to 75%.

Any idea what might be causing this? My beers taste fine but I'm really not wanting 5-6% abv in beers that only have a 1.050 OG! Do I need to switch yeasts? Mash at a higher temp?

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Old 05-22-2012, 05:50 PM   #2
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At what temperature are you fermenting? A higher mash temp should reduce attenuation.

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Old 05-22-2012, 05:51 PM   #3
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Your thermometer may be off and you may be mashing a lot lower than you think you are.

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Old 05-22-2012, 06:05 PM   #4
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Originally Posted by helibrewer View Post
At what temperature are you fermenting? A higher mash temp should reduce attenuation.
I have a Johnson temp control running my fermentation chamber which I set at 60F for the first 7 days and then 65F for the rest of the 21 day primary. My beer temp never gets above 66F according to my temp strips which I wrap a towel around to be sure they are measuring FV temp and not air temp.

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Your thermometer may be off and you may be mashing a lot lower than you think you are.
I was wondering if this could be my problem. I mash at a measured 150-154F but my thermometer is just a lab thermometer like this:



What is the best way to calibrate it?
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Old 05-22-2012, 06:09 PM   #5
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How long are you mashing for?

It is some combination of too low mash temp and too long of a mash. And grain bill, of course. It is not the fermentation temp.


You can calibrate using the standard ice bath for the low end, and boiling water for the high end. That is no guarantee that the thermometer is accurate in the mash temp range, but at least then you'll know if it is systematically off in one direction or another.


Personally I feel that the attenuation numbers given by yeast vendors are more guidelines. As in, US-05 will tend to attenuate more than S-04 (mostly due to flocculation, IMO). However the mash and grain bill play such a huge role in attenuation that there is no way you can just use those numbers reliably and expect your beers to attenuate 75% or whatever. By tweaking my recipe designs I have gotten over 90% attenuation from US-05 for one recipe, and less than 70% for another.

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Old 05-22-2012, 06:13 PM   #6
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How long are you mashing for?

It is some combination of too low mash temp and too long of a mash. It is not the fermentation temp.


You can calibrate using the standard ice bath for the low end, and boiling water for the high end. That is no guarantee that the thermometer is accurate in the mash temp range, but at least then you'll know if it is systematically off in one direction or another.

I mash for 60 minutes and batch sparge with 168F water. My mash temp tends to stay pretty stable, maybe dropping 2 degrees F in 60 minutes.

I can give that a try. What types of thermometers are the most accurate? Seems like a lot of homebrewers are using digital probes for their mash tuns.
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Old 05-22-2012, 06:16 PM   #7
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How long is your sparge?


I use a thermapen but it is rather pricey. However, it totally rocks as a thermometer. I know plenty of folks use some of the cheaper digital instant-read thermometers and like them.

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Old 05-22-2012, 06:19 PM   #8
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Quote:
Originally Posted by weirdboy View Post
How long is your sparge?


I use a thermapen but it is rather pricey. However, it totally rocks as a thermometer. I know plenty of folks use some of the cheaper digital instant-read thermometers and like them.
I sparge in 3 parts, usually about 1.5 gal per volume or as needed to reach my pre-boil volume in the brew pot. I pour the sparge water in, give it a stir, let it sit 3-5 min and then lauter my 2nd+ runnings that way. Is this an OK method?
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Old 05-22-2012, 06:21 PM   #9
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No I mean how long is your sparge, in minutes?

One thing that might be going on is that typically your sparge water might be 168, but your grain bed temp is lower, so you are still getting alpha and beta amylase the whole time you are sparging. If you have a longer mash/sparge in the range where beta amylase is still taking place, you are going to get a more fermentable wort.


EDIT:

However, this whole line of reasoning is a bit of a stretch. My money is on the mash temps being lower than you think. I would just increase your target mash temp a couple of degrees on your next brew and see how that ferments out.

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Old 05-22-2012, 07:38 PM   #10
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Quote:
Originally Posted by weirdboy View Post
No I mean how long is your sparge, in minutes?

One thing that might be going on is that typically your sparge water might be 168, but your grain bed temp is lower, so you are still getting alpha and beta amylase the whole time you are sparging. If you have a longer mash/sparge in the range where beta amylase is still taking place, you are going to get a more fermentable wort.


EDIT:

However, this whole line of reasoning is a bit of a stretch. My money is on the mash temps being lower than you think. I would just increase your target mash temp a couple of degrees on your next brew and see how that ferments out.
I think you are asking how long I leave the sparge water in the grain bed but you could also mean how long does it take to lauter the sparge through as wort runnings. I actually pour in water that is about 174F so that my grain bed/water temp rises to 167/168F for 3-5 minutes, then lauter for about 3-5 minutes more.

I actually mashed my last brew (currently in primary) at a higher temp to see if it makes a difference. I mashed at an "indicated" 156F with the same thermometer. We shall see! thanks for the advice so far.

- J
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