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attenuation always higher than yeast mfg says

Ilovebeer

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I have looked back at many of my batch records and find that my apparent attenuation is almost always above the range advertised by the yeast manufacturer, or at worst at the very high end. Sometimes the AA is way higher (92 vs 77 max yeast). This is true of malty beers mashed at 158 as well as light body beers mashed at 148 and everything in between. It happens with super heavy imperial stout at 1.042 FG to tripels at 1.000. I take OG readings with refractometer, but always check calibration with RO water. I take FG readings with an FG hydrometer, also checked with RO water and corrected for temp. I use Mr. Malty or Beersmith for yeast starter calcs, although they do not have input for O2 + stir plate, and I use both. I also use O2 in the fermentor at pitch.
My final gravities are typically very close to estimated or a few points below, sometimes as much as .008 below. I am happy with my beers and do not feel like they are overly dry, often have a lot of sweetness.
So I really don't have anything to complain about, but just would like to know what might cause the discrepancy
 
Ilovebeer said:
I have looked back at many of my batch records and find that my apparent attenuation is almost always above the range advertised by the yeast manufacturer....  So I really don't have anything to complain about, but just would like to know what might cause the discrepancy

Well, obviously it's you!  :D  Or at least your fermentation techniques. Sounds like a good problem to have!

Since you have records and can create averages from them, you can update your yeasts in the ingredient database to reflect your real world experience. New recipes will now reflect your results. Since it may be your technique, you can anticipate the average increased attenuation as a possibility for other yeasts, too. Just update their maximum attenuation, since this is the field BeerSmith uses to calculate from.

One other thought to ask, though. What temperature are you measuring the FG at? And is your hydrometer calibrated? Hydrometers are temperature sensitive, so being above their range will lead to a lower reading. Conversely, being colder will raise the reading.

 
Another possibility is that the thermometer that you're using is out of calibration.  if it's measuring your mash at 156 degrees F. and you're actually down around 150 degrees F., then you'll have a more fermentable wort, which would allow the yeast to attenuate more of the wort.

I'd check your thermometer, to make sure it is accurate.
 
Another possibility may be your hydrometer is incorrectly calibrated. Or perhaps you use a refractometer that needs recalibration and/or the formula for post-pitching compensation needs to be checked?
 
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