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General Category => Yeast and Fermentation => Topic started by: Pi on August 11, 2011, 08:50:58 PM

Title: Low attenuation please help
Post by: Pi on August 11, 2011, 08:50:58 PM
I cant seem to figure it out. Tried using spring water, bottled water; extract brewing; well aireated/oxygenated wort; adherence to recomended pitching rates and fermentation temps, but still getting roughly 50%ADF when i should be getting 75. I did two seperate Identical batches using the Pilsner Urquell clone recipe discussed in Zymurgy (July/August 2011) Double decoction vs triple, OG 11.6P. After racking to secondary i'm getting like 5.9P. In past experience, after a 4 week lager, I'm lucky if I get anything lower than 5.5P. What gives?
Title: Re: Low attenuation please help
Post by: denny on August 11, 2011, 09:25:55 PM
Are you measuring with a refractometer?  If so, are you using a correction for the alcohol?
Title: Re: Low attenuation please help
Post by: eltharyon on August 11, 2011, 09:48:37 PM
I know you did a decoction but is there any chance you might have heated too much grain or done something else to have damaged the enzymes to prevent further fermentation?

Title: Re: Low attenuation please help
Post by: Hokerer on August 12, 2011, 12:14:28 AM
I suspect Denny might have hit it with the refractometer thing.  Something else to check might be the calibration of whatever thermometer you're using to determine mash temp.  If that's far enough off, that could do it too.
Title: Re: Low attenuation please help
Post by: Pi on August 12, 2011, 06:36:52 PM
Are you measuring with a refractometer?  If so, are you using a correction for the alcohol?
Not sure I know what you mean Denny. Take readings ending sparge; start/end of boiling; andSG from the fermenter. Pro Mash is measuring/calculating what I am giving from those readings. Am I missing something? Thanks.
Title: Re: Low attenuation please help
Post by: denny on August 12, 2011, 06:45:19 PM
Are you measuring with a refractometer?  If so, are you using a correction for the alcohol?
Not sure I know what you mean Denny. Take readings ending sparge; start/end of boiling; andSG from the fermenter. Pro Mash is measuring/calculating what I am giving from those readings. Am I missing something? Thanks.

If you use a refractometer to take a gravity reading after the beer has been fermenting, the presence of alcohol will throw the reading off.  You need to use a correction factor in order to get an accurate reading.
Title: Re: Low attenuation please help
Post by: Pi on August 12, 2011, 06:52:28 PM
I know you did a decoction but is there any chance you might have heated too much grain or done something else to have damaged the enzymes to prevent further fermentation?


Usually I pull about1/3-1/2 the main mash (8 to 10l.) to go from beta to alpha to knock out rests. these amounts bring me to just below my target temp., which I gradually raise to my setpoint. I am using a RIMS btw so I'm pretty sure I'm getting accurate temp. readings (taking from just past the heater {thermocouple to PID} and middle of mash tun). Just thought of something: do you think the flow rate thru the grain bed has any+ or - effect? Getting similar attenuation from step/multi step mashes as well.  
Title: Re: Low attenuation please help
Post by: Hokerer on August 12, 2011, 07:01:00 PM
Are you measuring with a refractometer?  If so, are you using a correction for the alcohol?
Not sure I know what you mean Denny. Take readings ending sparge; start/end of boiling; andSG from the fermenter. Pro Mash is measuring/calculating what I am giving from those readings. Am I missing something? Thanks.

Taking your 11.6 start and 5.9 finish refractometer readings and applying the alcohol correction (via Sean's spreadsheet) says that you got FG 1.010 which is about what you'd expect.
Title: Re: Low attenuation please help
Post by: Pi on August 12, 2011, 08:39:48 PM
Are you measuring with a refractometer?  If so, are you using a correction for the alcohol?
Not sure I know what you mean Denny. Take readings ending sparge; start/end of boiling; andSG from the fermenter. Pro Mash is measuring/calculating what I am giving from those readings. Am I missing something? Thanks.

Taking your 11.6 start and 5.9 finish refractometer readings and applying the alcohol correction (via Sean's spreadsheet) says that you got FG 1.010 which is about what you'd expect.
I think that's it! Where can i find Seans spreadsheet?
Title: Re: Low attenuation please help
Post by: a10t2 on August 12, 2011, 08:46:41 PM
I think that's it! Where can i find Seans spreadsheet?

Download links are at the bottom of this page: http://seanterrill.com/2011/04/07/refractometer-fg-results/

Although if you google "Sean's spreadsheet" it's on the first page. :o
Title: Re: Low attenuation please help
Post by: Pi on August 13, 2011, 09:31:01 PM
WHOAA!!!
Went back last night and played with my ProMash SW. i found out that ProMash does this correction for you! Just looked at Sean's spreadsheet and that explains things. Since then i have been going back correcting my FG and everything works out on the money. I feel like such an idiot. here i was thinking i need to add more grain to get the alcohol i was looking for. Meantime I'm having a homebrew (That's already bumped up). Thanks to all for helping me out.
Title: Re: Low attenuation please help
Post by: a10t2 on August 13, 2011, 11:00:44 PM
i found out that ProMash does this correction for you!

Well... Yes, it does do a correction. It's just wrong.
Title: Re: Low attenuation please help
Post by: tschmidlin on August 14, 2011, 04:09:24 AM
WHOAA!!!
Went back last night and played with my ProMash SW. i found out that ProMash does this correction for you! Just looked at Sean's spreadsheet and that explains things. Since then i have been going back correcting my FG and everything works out on the money. I feel like such an idiot. here i was thinking i need to add more grain to get the alcohol i was looking for. Meantime I'm having a homebrew (That's already bumped up). Thanks to all for helping me out.
So you are using a refractometer and not a hydrometer, right?  I don't think I saw where you confirmed that.
Title: Re: Low attenuation please help
Post by: Pi on August 15, 2011, 03:52:27 PM
Yes, using a refractometer. I think I'll do a couple samples using both and see how accurate ProMash is.
Title: Re: Low attenuation please help
Post by: denny on August 15, 2011, 03:57:25 PM
Yes, using a refractometer. I think I'll do a couple samples using both and see how accurate ProMash is.

You'll get much better results using Sean's spreadsheet for correction than Promash.
Title: Re: Low attenuation please help
Post by: a10t2 on August 15, 2011, 04:00:32 PM
Yes, using a refractometer. I think I'll do a couple samples using both and see how accurate ProMash is.

If you're willing, please share the results.