[MDixon]

So sometimes I'm thick. Fred said a pound of sugar in 5 gallons would lower the FG by 0.0027, for some reason I just can't get my brain around where that comes from...perhaps too much travel.

I'm thinking a pound of sugar is 45 pts (some say more, some say less). 45/5 = 9 pts per gallon, the sugar essentially ferments to completion leaving 1.000 out of the 1.009 we started with. Of course that is a pure sugar/water ferment. Take me the rest of the way to the 0.0027 since I'm not coming up with it...(where's the head scratching emoticon when needed)

[jeffy]

So sometimes I'm thick. Fred said a pound of sugar in 5 gallons would lower the FG by 0.0027, for some reason I just can't get my brain around where that comes from...perhaps too much travel.

I'm thinking a pound of sugar is 45 pts (some say more, some say less). 45/5 = 9 pts per gallon, the sugar essentially ferments to completion leaving 1.000 out of the 1.009 we started with. Of course that is a pure sugar/water ferment. Take me the rest of the way to the 0.0027 since I'm not coming up with it...(where's the head scratching emoticon when needed)

Me, too.  Please explain.
I thought maybe they were saying that the hydrometer reading would change because of the increased alcohol.  Perhaps it has to do with apparent attenuation instead of actual, calculated attenuation, which accounts for the increase in alcohol.

[MDixon]

I thought about that and still couldn't wrap my head around it. If I threw in a pound of sugar into 5 gallons of a 1.045 beer I take the OG to 1.054. With an 85%AA of the initial wort (1.045), it would have finished at ~1.007, the sugar component should go to completion or 100%AA, so it must be in there somewhere, but the brain ain't what it once was...

[bbkf]

adding sugar to "lighten body" is to raise the alcohol a touch without added dextrins.  if you had a 7% alcohol beer that you wanted to be 7.5% or 8%, adding more malt to get to that extra alcohol would add more body.  But, if you add sugar instead, you'll get the extra alcohol without adding to the mouthfeel.

[MDixon]

I certainly hope everyone understands how/why sugar is utilized in brewing...I'm looking for the mathematical proof of Fred's statement...

[tomsawyer]

Ethanol has a specific gravity of 0.8 or thereabouts.  Thats why added sugar will lower the FG very slightly, more of a low gravity solvent in your aqueous solution.

Wine is typically 12-15% ABV, and when it ferments dry it is typically 0.99 FG.

[tygo]

It's a matter of apparent attenuation.  

Let me take a shot at this with the caveat that I need more coffee before I'm fully functioning.

Let's assume the beginning OG of 1.045 and 85% AA yielding an FG of 1.00675.  1 lb of sugar in 5 gallons would add 1.19% ABV according to Beersmith.  So let's say that adds 7.6 oz of volume (5 gallons x 128 oz x 0.0119) which ferments out completely and produces that volume of pure ethanol at a SG of 0.794.  

So we've got 640 oz at an FG of 1.00675 and 7.6 oz at an FG of 0.794.  That makes the final volume 640 + 7.6 = 647.6 oz

FG = (640 x 1.00675) + (7.6 x 0.794) = 650.3671 / 647.6 = 1.00425

1.00675 - 1.00425 = 0.002502  <---- Drop in FG due to adding 1 lb of sugar.

[jeffy]

So it is apparent attenuation then.  Here's something I found on the homebrew wiki that has a calculation that Fred may have used:

Apparent vs. Real Extract

Hydrometers are calibrated for measuring the sugar (extract) content of a water solution. This is true for wort. But when used to measure the extract of beer, which contains ethanol, the reading will be skewed by the lower specific gravity of the ethanol. As a result the hydrometer shows a lower extract content than the actual beer has. This measured extract value is called apparent extract (as opposed to the real extract that is measured when there is no alcohol in the solution) and is commonly used when refering to the extract (or specific gravity) of beer. Like the real extract it can be expressed as weight percent, degree Plato or specific gravity. To determine the real extract one can boil-off the alcohol and replace it with distilled water before using a hydrometer. Or, if the original extract is known, the following formula [Realbeer] can be used to calculate the real extract from the apparent extract:

real extract = 0.1808 * original extract + 0.8192 * apparent extract
[edit] Apparent vs. Real Attenuation

When the apparent extract of the beer is used to calculate its attenuation it is called apparent attenuation. The use of the real extract will give the real attenuation. When brewers speak of just attenuation they are most likely to mean apparent attenuation since it can easily be calculated from the hydrometer readings.

[bluesman]

In the case of the OP...he has a beer that starts at 1.042 and ferments down to 1.011 for an AA%=75.

If he adds a pound of sugar (table) at 46ppg/5gal = 9.2 gravity units which will increase his OG to 1.0512. He'll ferment out all of the sugar (table) and 75% of the sugar from the original wort.

.75 (AA%) * 42 (GU) + 1.00(AA% of sugar)/.79 * 9 (GU) = 42.9 GU

51.2 - 42.9 = 8.3 GU = 1.0083 finishing gravity

So by adding the sugar the AA% increases by 5% and the finishing gravity is reduced by .0025 thus slightly altering the mouthfeel (reducing) of the finished beer.

[tygo]

Bluesman - Your calculation assumes that the sugar that's added will ferment out to a volume with a SG of 1.000.  Really it will ferment out to a volume with the SG of ethanol or 0.794.

[bluesman]

Bluesman - Your calculation assumes that the sugar that's added will ferment out to a volume with a SG of 1.000.  Really it will ferment out to a volume with the SG of ethanol or 0.794.

Correct.

My bad. I corrected the calculation to account for this. There's a reduction in the final gravity as shown in my previous post.

[bonjour]

The numbers came from Palmer's book.

The "Real" attenuation is less. Pure ethanol has a gravity of about 0.800. If you had a 1.040 OG beer and got 100% real attenuation, the resulting specific gravity would be about 0.991 (corresponding to about 5% alcohol by weight).

http://www.howtobrew.com/section1/chapter6-1.html

The key here is that a pure (No Malt to muddy the calculations) alcohol in water will have a FG < 1.000
Per the above statement a 1.040 OG "beverage" will have a FG of 0.991

The rest is based on how much sucrose it takes to get 1.040.  This much sucrose in (pick 5 gallons) will yield a measured FG of (per Palmer above) a FG of .991.  Simple ratios will take you to the result.

Thus a pound of sucrose (chosen because sucrose does not  bind water into it's matrix, it is not hydroscopic, again to not cloud the computation.

[MDixon]

Thanks guys, I figured it was something like that, but such an absolute number threw me for a loop and my four function calc and one cup of coffee brain just wasn't cutting the mustard on this one...

[stlaleman]

Thanks for all the input. I ended up adding sugar to the wort. I'll post the gravity when I dump the yeast next weekend. This turned into a most interesting discussion.

[stlaleman]

Fermentation is over, the beer has "cleared" as much as a saison does. Dropped to 1010, high end of the scale for style. It turned out very nice, pepperry aromas with intense fruit, can't wait to get it carbed and drink!