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General Category => Yeast and Fermentation => Topic started by: saed on September 01, 2011, 11:44:08 PM

Title: Attenuation
Post by: saed on September 01, 2011, 11:44:08 PM
Hello there. I have been brewing for a long time but recently, I noticed my attenuation is really low. The final gravity always come more than what it should be, thus the % ABV is low. This happened for a dopple bock and with a red ale that I used WLP001, which is quite versatile. I always start my yeast few days before I brew and for the red ale even I started with two liquid yeasts and added 1/2 gallon yeast and starter to 10 gallon wort. Any ideas?
Title: Re: Attenuation
Post by: tygo on September 02, 2011, 01:04:35 AM
Are you making extract or all-grain batches?
Title: Re: Attenuation
Post by: Hokerer on September 02, 2011, 02:33:36 AM
And how are you measuring your gravities?
Title: Re: Attenuation
Post by: hoser on September 02, 2011, 03:07:30 AM
We need more info: extract or all grain, mash temps if all grain, pitching temps, ferment temps, starter size, stir plate, oxygenation, how are you measuring gravities and your attenuation, are these instruments calibrated, how much crystal malts or adjunct, what are you getting for numbers that leads you to believe your attenuation is low?
Title: Re: Attenuation
Post by: bonjour on September 02, 2011, 01:30:40 PM
We need more info: extract or all grain, mash temps if all grain, pitching temps, ferment temps, starter size, stir plate, oxygenation, how are you measuring gravities and your attenuation, are these instruments calibrated, how much crystal malts or adjunct, what are you getting for numbers that leads you to believe your attenuation is low?
+1

You left out times, mash times, primary time, secondary time. 
So much impacts attenuation that we really need to understand your entire brewing process in detail, from grain/extract to bottle/keg.
Title: Re: Attenuation
Post by: saed on September 02, 2011, 07:01:02 PM
Hello again and thank you for the questions. Here are some more info:
I did all grain. Mash included 5.5% Crystal 40 and 3.2% Crystal 120. I mashed at 155 to 158 for 90 minutes. The boil time was 90 minutes and I pitched the yeast at 73 F where OG was 1.070. The starter was 1/4 gallon for 5 gallon and started it two days before that. I did not use any adjucts, except Irish Moss for clarity 15 minutes left to end of boil. No stir plates or oxigenation and the fermentation started after 6 hours. I have floating thermometer and floating hydrometers. I always adjust for temperature from the tables provided. The primary was for 8 days and it is in the secondary now but does not look like there is any activity going on. I measured the gravity at it was 1.023 and from the experience it does not go down much in the secondary.

Thank you all for your help.
Title: Re: Attenuation
Post by: bonjour on September 02, 2011, 07:17:13 PM
Hello again and thank you for the questions. Here are some more info:
I did all grain. Mash included 5.5% Crystal 40 and 3.2% Crystal 120. I mashed at 155 to 158 for 90 minutes. The boil time was 90 minutes and I pitched the yeast at 73 F where OG was 1.070. The starter was 1/4 gallon for 5 gallon and started it two days before that. I did not use any adjucts, except Irish Moss for clarity 15 minutes left to end of boil. No stir plates or oxigenation and the fermentation started after 6 hours. I have floating thermometer and floating hydrometers. I always adjust for temperature from the tables provided. The primary was for 8 days and it is in the secondary now but does not look like there is any activity going on. I measured the gravity at it was 1.023 and from the experience it does not go down much in the secondary.

Thank you all for your help.
The biggest culprit in low attenuation is mash temp.  Based on your mash temps, your FG is around where I'd expect it.
Higher mash temps typically yield lower attenuation and higher FGs.  How much really depends on your system and your processes so there is no magic formula to calculate it.  If you learn your system you can reasonably accurately predict it.  That takes time and experience with specific malts and yeasts.
Title: Re: Attenuation
Post by: richardt on September 02, 2011, 07:19:30 PM
What Fred said.  You're mashing too high.

Also, check and calibrate your thermometer.  It may be reading lower than actual temps (e.g., reading 155F when it actually is 159 or 160 F)--not a good thing for your enzymes. 
Title: Re: Attenuation
Post by: hoser on September 02, 2011, 07:36:27 PM
Mash temps may be a factor, but I know for a fact Lagunitas mashes at 158-160F on their IPA and that is fairly well attenuated.  I think the biggest culprit is how he is handling his yeast.  He is pitching way too warm, dare I say HOT!  His starter is too small for a 1.070 beer, he is underpitching.  No oxygenation.  And he is likely transfering to the secondary before the yeast is finished.

My recommendation is:
Get a stirplate, flask, and stir bar for a starter
Yeast nutrients
Pitch appropriate amounts using the calculator on mrmalty.com
Oxygenate
Pitch at appropriate fermentation temps
Transfer off the yeast cake only after gravity readings have been stable for 2-3 days.

Do these things and not only will your beer attenuate beer, it will improve overall!
Title: Re: Attenuation
Post by: jeffy on September 02, 2011, 07:37:14 PM
Yes to the above, but also you mentioned that you did not oxygenate.  Next time make sure to aerate the cooled wort well for better yeast growth.
Title: Re: Attenuation
Post by: weithman5 on September 02, 2011, 07:56:40 PM
mash temp and ferm temp have impact. that said i did a quick run on the computer for that starter gravity and yeast i get finishing gravity of 1016.  i don't think you are so far off that you need to look farther than those two problems - and some oxygen. to close in on your targets
Title: Re: Attenuation
Post by: hoser on September 02, 2011, 08:04:42 PM
A fast ferment test might give you some valuable information?  My best guess is you are under pitching at hot temps with no aeration/oxygenation and nutrients.  The yeast are working super fast, but then crap out when they run out of oyxgen/nutrients before the beer has finished fermenting.  I hope you did not pitch that doppelbock at 73F!?!?!
Title: Re: Attenuation
Post by: saed on September 02, 2011, 08:52:05 PM
Thank you all for your input. My digital thermometer was showing the mash temp at 152 F but when I measured it with two other thermometers, I found it it was higher. It was too late though. As far as oxigenation, I do not add oxygen directly but aerate the wort pretty good after adding the yeast.

Thank you again!
Title: Re: Attenuation
Post by: rightasrain on September 03, 2011, 03:09:32 AM
The biggest culprit in low attenuation is mash temp.  Based on your mash temps, your FG is around where I'd expect it.
Higher mash temps typically yield lower attenuation and higher FGs.  How much really depends on your system and your processes so there is no magic formula to calculate it.  If you learn your system you can reasonably accurately predict it.  That takes time and experience with specific malts and yeasts.

Is there any tricky way to tell the difference between a low attenuation and a stalled fermentation?
Title: Re: Attenuation
Post by: hoser on September 03, 2011, 04:00:50 AM
The biggest culprit in low attenuation is mash temp.  Based on your mash temps, your FG is around where I'd expect it.
Higher mash temps typically yield lower attenuation and higher FGs.  How much really depends on your system and your processes so there is no magic formula to calculate it.  If you learn your system you can reasonably accurately predict it.  That takes time and experience with specific malts and yeasts.

Is there any tricky way to tell the difference between a low attenuation and a stalled fermentation?

A fast fermentation test