Attenuation of gravity with addition of sugar.

[rcjung]

Knowing that sugar (sucrose or dextrin, cane or corn) has a higher potential to produce alcohol than malt, it is corretly to consider ABV increase in beer, but the attenuation of OG should not be calculated using this higher potential. That is, when I add sugar in the recipe, the FG gets too low. The correct way is to calculate attenuation of the OG only with the percentages that the yeast is able to attenuate, disconsidering, in this calculation, the greater potential that the sugar has to produce alcohol. In the picture, I created a recipe to demonstrate and, calculating correctly, the FG would be between 1.012 and 1.013

 

[Oginme]

Respectfully, I am not sure I follow what you are stating.  The addition of sugar adds to the OG of the resultant wort.  BeerSmith, and other programs, usually calculate the attenuation of the gravity based upon the apparent attenuation values for the yeast as applied to that percentage of the wort potential which is derived from malt (since that is how those attenuation numbers are measured) and then the sugars are calculated to ferment completely.  This, in effect, covers what I think you are stating in your message. 

The additional attenuation due to the sugar increases the apparent attenuation of the yeast  beyond the published values.  For instance, WY1214, Belgian abbey ale, has an apparent attenuation of 74% to 78% based upon the Wyeast website.  When I use this yeast in my Belgian Tripel, I get a measured apparent attenuation of 86% due to the high use of sugars.  That sugar adds 15 points to the OG of the wort, all of which ferments.  This effect increases the OG and also lowers the FG, since there is no residual gravity from the sugars. 

If you have some literature that contradicts this, please link to it as I would be most interested in reading the theory behind it.

 

[rcjung]

" This effect increases the OG and also lowers the FG, since there is no residual gravity from the sugars.  "


About FG, I will get the information and soon post the result. 

 

[rcjung]

So, I did a test:

1) 15 liters of wort (mash at 64.4?C - Pilsner malt): 1.022 SG
2) 900 grams of cane sugar: 1.023 SG
3) 9.8 grams yeast Fermentis S-04 (viability 73.29%)

Measured OG: 1.045
Fermentation: 7 days between 18?C - 20?C
Measured FG: 1.010
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Estimated FG by yeast:
Maximum Attenuation 75% - FG 1.014
Minimum Attenuation 71% - FG 1.012
Average Attenuation 73% - FG 1.013

Estimated FG by BeerSmith: 1.001
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Conclusions:

1) the attenuation adjustment by mash temperature should be done.
2) the sugars should not be calculated to ferment completely, they should only be calculated on the percentage that the yeast can attenuate.

 

[Oginme]

Not quite sure I can get there from your test.  A more proper test would be to take a wort at 1.045 made with your pilsner malt mashed at 64.4C (148F) and a wort with just sugar at 1.045 gravity and ferment those separately with the same amount of yeast.  Ferment these out and check the FG of each.

Since the apparent attenuation results for a yeast are tested on a all-grain wort, it does not apply fully to the same yeast acting upon sugar.

In another side note, I tried to get your estimates on my copy of BeerSmith 3 and it appears as though you have turned off the option to adjust fermentability based upon mash temperature.  This is a feature already set in BeerSmith and can be accessed by clicking on 'options' > 'advanced'.  When I initially put your recipe into my copy of BeerSmith, it gave me a FG estimate of 0.999.  When I turned off the 'adjust FG for mash temperature', I get your estimated result of 1.001.

 

[rcjung]

Yes, at that time the option was disabled, I was making comparisons, but I leave it turned on when I create new recipes. This feature works great.

The fermentation of wort with just sugar and the amount of yeast suggested by BeerSmith, I believe will not attenuate more than the maximum percentage that the yeast manages to reduce. I'm not saying that this amount is wrong. This amount is right, I use it in my fermentations and always get great results. I'm just saying that for the complete fermentation of sugar, more yeast will be needed than was suggested.

I'll do the test as soon as the weather warms, it's winter here.. lol

 

[BOB357]

Attenuation percentages specified for yeasts by the producers are not telling you what percentage of available sugars will be eaten by the yeasts. They are values based on comparing the attenuation of various strains in a specific wort. When the wort changes so does the attenuation.

More fermentable worts will obviously more fully attenuate as long as the fermentation isn't stopped by other factors. Some of these factors are temperature,early flocculation, running up against the strains alcohol tolerance, failure to pitch an adequate amount of healthy yeasts, Lack of dissolved oxygen at, or immediately after pitching and lack of proper yeast handling.