Welcome to the new forum! We upgraded our forum software with a host of new boards, capabilities and features. It is also more secure. Jump in and join the conversation!
You can learn more about the upgrade and new features here.
How are you measuring your FG? If you are using a refractometer, then you must adjust the reading to account for the alcohol content of the beer. The difference in refractive index of the beer (containing alcohol) makes the scale of your refractometer (calibrated for sugar) incorrect. BeerSmith does allow for correction of the FG based upon the refractometer reading and the original gravity in the refractometer tool.
Ah, I get it. I would need to see the recipe to determine what is up. If you export it as a .bsmx so we can look at it in BeerSmith, we can see and make specific recommendations.
In the meantime, I took your OG as 11.06 Brix or Plato. Did you actually mean to type 1.106? If this is the case, then the program may be defaulting to the maximum alcohol tolerance of the yeast that you are using and capping the FG based upon that %ABV. You can check this by going into the recipe and editing the yeast specifications. Increase the maximum %ABV up and save. If you see a change in the FG and %ABV, then this was your problem.
OK. In BeerSmith 3, the ability of the yeast to turn those sugars into alcohol is capped by the individual yeast strain and the alcohol tolerance of that yeast. US-05 has a maximum alcohol tolerance of 10% in the BeerSmith profile and an attenuation of around 76.5% (average of max and min) which when applied to a gravity of 1.106 would give you a projected FG of around 1.025 with an alcohol content of around 11%. Since this is above the 10% max for the yeast, the program caps the ABV at 10% and projects an FG of 1.035 (actual value varies depending upon mash conditions).
The amount of yeast you pitched does not matter to the software, which does not know this information. What does matter is the specifications of the yeast strains which imposes a limit on the amount of alcohol before the yeast will not function (right or wrong is another issue all together).
In your recipe, edit the yeast by double clicking on it in the design box. Change the maximum alcohol tolerance to 12% and see where the estimation of FG comes in. If your wort was all grains of extract, I would estimate that it would be somewhere in the range of the 1.025 I calculated above. (again, mash conditions will affect the actual number, which is why the actual recipe makes a difference). If you have some simple sugars in the recipe, then the number will be lower than that.
Edit: Your actual value of 1.020 is not out of the question, since the maximum attenuation of US-05 is 80% and going from 1.106 down to 1.020 is around 79.7% attenuation. Well within the capabilities of the yeast. Thus further indicating that the software limit of 10% for that strain may be incorrect and providing an erroneous FG.