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How to adjust attenuation for yeast

yso191

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I consistently have a much higher attenuation than what BS predicts.  One of the yeasts I use the most is Wyeast 1968 (London ESB).  It is consistently over attenuated by 9-11 points every time I use it.  For example BS predicts a FG of 1.018 and comes out 1.007.  That being the case, by how much should I adjust the Max and Min Attenuation for that yeast profile?
 
Have you checked the calibration of your hydrometer?
If you are mashing at a low 145-148 you will attenuate lower.
If there are no residual sugars in your grain bill, you will end up lower.
 
RiverBrewer said:
Have you checked the calibration of your hydrometer?
If you are mashing at a low 145-148 you will attenuate lower.
If there are no residual sugars in your grain bill, you will end up lower.

I use a refractometer and use the correction tool in BS to arrive at the FG number.  And yes it has been calibrated several times.  I understand the principle behind your points 2 & 3.  The issue is that this has only been occurring with this yeast, and it is across a number of brews.  So with it being consistent, I'd like to know how to fix it so it consistently is accurate in its prediction.  I'm thinking there must be a formula for determining how much to change the Attenuation percentages based on the consistent 9-11 points of difference.
 
A refractometer doesn't measure specific gravity, just the the sucrose of the wort, or wort gravity. In order to make the tool do the calculation to convert to SG you have to calibrate every wort, since there are more sugars present than just sucrose in any given batch. To calibrate the wort, you need a hydrometer reading to get the brix correction factor or else your calculation will be off. Not only do you need to calibrate the refractometer you have to calibrate the wort. A simple and accurate way to check the gravities is with a hydrometer. Maybe its just me... I like things uncomplicated!

Good luck with your correction calculation!

Just enter the ingredients section, yeast, 1968, and edit the max and minimum attenuation until you get the number your looking for.

Just wondering if the yeast is from the same date or across the spectrum. If the later, it is great quality control.
 
I think the estimated attenuation for 1968 is a little too conservative, whether that's in BS or in the product's literature. I used that recently (for the first time) on a medium body porter that should have stopped around 1.015--instead, I wound up at 1.008. This was after two weeks in primary with no starter, and an OG of 1.053. The beer tastes great, so I'm not complaining, but it's definitely drier and boozier than I was expecting or desiring.

I'll admit to not doing a lot of research in these things--I'm sort of a fly-by-night-courtesy-of-the-seat-of-my-pants brewer--but have you compared Wyeast's specifications for this particular strain to what is recorded in BeerSmith?
 
cmbrougham said:
I think the estimated attenuation for 1968 is a little too conservative, whether that's in BS or in the product's literature. I used that recently (for the first time) on a medium body porter that should have stopped around 1.015--instead, I wound up at 1.008. This was after two weeks in primary with no starter, and an OG of 1.053. The beer tastes great, so I'm not complaining, but it's definitely drier and boozier than I was expecting or desiring.

I'll admit to not doing a lot of research in these things--I'm sort of a fly-by-night-courtesy-of-the-seat-of-my-pants brewer--but have you compared Wyeast's specifications for this particular strain to what is recorded in BeerSmith?

Good thought!  And the answer is that I don't remember.  However, I just checked it and it is the same on Wyeast's site as in BeerSmith.
 
RiverBrewer said:
A refractometer doesn't measure specific gravity, just the the sucrose of the wort, or wort gravity. In order to make the tool do the calculation to convert to SG you have to calibrate every wort, since there are more sugars present than just sucrose in any given batch. To calibrate the wort, you need a hydrometer reading to get the brix correction factor or else your calculation will be off. Not only do you need to calibrate the refractometer you have to calibrate the wort. A simple and accurate way to check the gravities is with a hydrometer. Maybe its just me... I like things uncomplicated!

Good luck with your correction calculation!

Just enter the ingredients section, yeast, 1968, and edit the max and minimum attenuation until you get the number your looking for.

Just wondering if the yeast is from the same date or across the spectrum. If the later, it is great quality control.

I have heard that refractometers are not spot-on for reading fermented/ing wort, but are close enough.  Otherwise what would be the point of BeerSmith having the correction tool?  I agree that a hydrometer is simpler and easier, but for me, getting a clear (yeast/trub free) sample is often an issue.  Using a pipette to suck a small sample off the top seems much easier.

It very well could be that I am missing something in this whole process though.  Perhaps if I came over to your house and you showed me how you do it the light bulb would go on!  Do you live near Yakima?  ;)
 
I brew on the opposite side of the country. This is a link to explain how to calculate your attenuation.
 
  www.whitelabs.com/beer/homebrew/beginners-attenuation-and-flocculation-definitions

Since you need the Original Gravity (OG) you have to do the calculation. I would enter it this way, for example, if you calculate it out to 87%, enter minus 2% for minimum attenuation (85%) and add 2% for maximum attenuation (89%)

Hydrometer testing
I use a Fermtech wine thief for pulling samples out of buckets or carboys. It is easy to sanitize. If you have a krausen just put your palm over the end of the thief as you push through it to get a cleaner sample. If your doing all grain, slowly open your mash tun valve and run out some wort (I use a 2 cup pyrex measuring cup) and pour it back into the mash until your filter bed eliminates solid particles and clears if the color is light to check 1st runnings.
 
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