Overshooting ABV

General Homebrew Discussion
1

For me, one of the most consistently missed predictions in BeerSmith is Final Gravity/ABV.  This is not a big deal for me, but it is a curiosity so I hope someone here can give me some insight into why.

Take for example my latest brew, a Scottish 80 Schilling.  BeerSmith’s estimated OG was 1.049 - I hit 1.053, so that accounts for part of the effect.

But the bigger issue and more consistent (even when I hit my target OG) is the predicted FG and the resulting ABV.  For this brew the prediction was a FG of 1.016, and 4.3% ABV.  My FG was 1.009 and 5.8% ABV.  This happens quite regularly.

Where should I start looking?

2

Maybe add a mashout step to your process?

3

I used to have the problem of beers finishing too low, but now I can’t seem to get them to finish low enough. Not sure why. Probably had something to do with water chemistry. I used to get beers finishing really dry with US-05 before I messed with water. Now, they don’t finish like that so much. Still learning after all these years.

4

If you are brewing all grain check your thermometer’s accuracy. That can result in lower or higher than expected FG. Also adjust your efficiency in your program. So your SG is more accurate.

5

Getting a good FG estimate from Beermith is pretty unlikely (I don’t use Beersmith’s mashing profiles).  I make my own best estimate for FG from experience.  Would be interesting to see if other software does a better job, but I doubt it.

White Labs was working on correlations for all of their yeasts to better estimate FG.  Not sure what the status  of that research is.

6

It also makes a difference on FG if you have the correct stats plugged in for the yeast you are using.

7

My own biggest issue is probably related primarily water volumes.  I may develop a recipe based on a 5.5 gallon fermentation volume, but more often I’m a lot closer to 5.  That half a gallon can obviously represent a significant difference in OG. As for FG, I just base ABV on the end results using the calculator tool in Beersmith.  I’ve never expected that value to be especially accurate in the recipe-builder, and I’m not exactly sure what goes into the Beersmith estimate.  I assume mash temp goes into the calculation, but I’ve never seen the function used.  Maybe we should ask Brad.

8

You should start by asking yourself why you think the prediction from BS is accurate!  It’s no more than a rough guess based on the attenuation rating of the yeast.  Your wort composition is what really matters.

9

But how can they know what your wort is like?  Using the same yeast I can get from 60-80+% attenuation depending on the wort.

10

The correlations were supposed to include mash temp.

11

I created a spreadsheet to track my efficiency, attenuation, etc. per batch. I can use these numbers to create graphs and visually see what trends are present. This is helpful to see what adjustments I need to make on my system/process to get my numbers where I want them. For instance, I may be getting 80% attenuation with US-05 on average when mashing at 154 when Beersmith says I should get 75%

The biggest thing for attenuation is the default values that Beersmith has loaded in for each strain. These aren’t necessarily accurate. The program basically takes the yeast strain coupled with your mash temperature to estimate attenuation. There is a setting where you can edit the attenuation slope per change in mash temperature. For each strain, I edit the min/max attenuation % for results that I have gotten. I recently moved and am getting different results. Before my attenuation was much higher so my ABVs were too high, now it is the oppossite. I chalk it up to a change in water since nothing else has changed… It will take me several more batches to get Beersmith more accurate with my system/process…

12

That’s minor.  What about 3 lb. of sugar vs. 3 lb. of crystal in an otherwise identical recipe?

13

Actually, your example sounds easy, but yes there are a lot of potential variables to be tested.  I think I heard about the research at the 2012 NHC.  Perhaps, the correlations didn’t work or were too difficult to develop.

14

For OG, it could be a finer crush or technique that’s getting you better efficiency. How are your volumes. If your pre-boil OG is right on, but you collect extra wort to account for boiloff, the extra water might extract extra sugar. If it’s consistently high, then pat yourself on the back and adjust the attenuation percentage in Beersmith.

For FG, that seems harder to diagnose. It could be mash temp, mash time, particulars about your recipe. Simple sugars are fully fermentable but Beersmith doesn’t seem to account for that. My first cheap digital thermometer was 10 degrees off.