Estimated final gravity in BS2

Hi,
While I've been playing with BS2 for a few months this is my first post on the forum.  My question is about how BS estimates final gravity.  I'm building a recipe that has a OG of 1.112 and BS is estimating a FG of 1.011.  That's an attenuation of > 90% and I'm pretty sure my yeast won't get there.  BS doesn't seem use the attenuation characteristics of the yeast I've selected (WL500) to make the estimate.  So how does it make this calculation?  It really throws the ABV off.  Thanks in advance for your help.

Chris Young

It does take into account yeast att. and mash temp.  I just created a couple of test recipes with 20 lbs of US pale malt in a 6gal batch for an OG of 1.102. 

WLP500 (80% Att)
  light-body, batch sparge  FG=1.015
  med-body, batch sparge  FG =1.019
  full-body, batch sparge    FG =1.024

WLP002 (70% Att)
  light-body, batch sparge  FG=1.025
  med-body, batch sparge  FG =1.030
  full-body, batch sparge    FG =1.035

If you look in the options page, on the advanced tab...you can see the options for controlling Fermentability vs Mash temp.

Remember that your FG will include the gravity lowering effects of the low-density alcohol.  You can add the apparent attenuation and real attenuation fields to the main recipe display, see the difference.    1.112 -> 1.011 is 89% apparent attenuation, but is only 73% REAL attenuation. 


 

Hi Tom and thank you for the reply.  I think I understand what you are saying and I added the RA field to my display (thanks for the tip).  So when the strain is listed at 75-80% attenuation, is it real attenuation they are talking about?  Thanks again for your help.

Chris Young

HI Chris-

Glad I could help.

Yes, the yeast strain attenuation number is REAL attenuation...the maximum percentage of fermentable sugars that the yeast strain will ferment, in ideal conditions.  Your actual results may be less than ideal. 

Don't forget to make a BIG starter for that barleywine---2L on a stirplate, or 4L without....or better yet, re-pitch from a lower gravity beer.  See http://www.yeastcalc.com/

tom_hampton said:

HI Chris-

Glad I could help.

Yes, the yeast strain attenuation number is REAL attenuation...the maximum percentage of fermentable sugars that the yeast strain will ferment, in ideal conditions.  Your actual results may be less than ideal. 

Don't forget to make a BIG starter for that barleywine---2L on a stirplate, or 4L without....or better yet, re-pitch from a lower gravity beer.  See http://www.yeastcalc.com/

Click to expand...

I'm thinking it has to be when presented with some form of maltose because if you present these yeasts with fructose or sucrose they go 100% up to alcohol tolerance.

And thanks for pointing out the temperature thing. I wondered how it knew to drop the FG when I lowered the mash temp. That will be a good one to tweak.

Yes, sorry... I should have said "fermentables in wort".  The attenuation difference between yeasts is mostly how well they can ferment maltotriose. 

tom_hampton said:

HI Chris-

Glad I could help.

Yes, the yeast strain attenuation number is REAL attenuation...the maximum percentage of fermentable sugars that the yeast strain will ferment, in ideal conditions.  Your actual results may be less than ideal. 

Don't forget to make a BIG starter for that barleywine---2L on a stirplate, or 4L without....or better yet, re-pitch from a lower gravity beer.  See http://www.yeastcalc.com/

Click to expand...

Yes, I'm doing a two step starter on a stir plate.  I should get something over 500 billion cells. 

About the mash temp effect on the estimated final gravity, I was wondering why when you mash under 63.9°C (~147 F) or over 70.8°C (~159 F), the estimated final gravity goes back to the average attenuation value set up in option/advance tab ? Anyone ever experimented it ?

I thought that the software would keep the FG to the same value as when mashing at lower temperature at least until you reach the lower range of the B-amylase (~55°C) and it should be the same for the upper range of the A-amyase (~75°C). Instead, as soon as you exceed the 63.9 or 70.8, the mean FG value is comming back which makes no sense to me.

Currently, there is an upper and lower limit to the mash calculation. Brad has said that the lower limit slope will be extended in a future update.

Keep in mind that starch doesn't quickly gelatinize under 65C (150 F). Very low temperature mashes at 60 C and lower starch doesn't fully gelatinize, so full conversion takes longer than the standard hour. More often than not, significant starch haze and stalled fermentations result.