How much sugar to add for desired OG

[Raptor99]

When I have used online calculators to determine how much sugar to add to attain my desired OG, the actual measured OG is often different from what I expect. I assumed that this would be a simple calculation, but apparently that is not so.

For my current hard lemonade, I was aiming for an OG of 1.040 in 1 gallon. I used several different online calculators, and got different results. Some of the calculators give the amount of sugar to add to 1 gallon of liquid. Others give the amount of sugar to add along with water to obtain a total volume of 1 gallon. These are not quite the same, since adding sugar increasing the volume of the water a little bit. In the figures below, I was looking for the amount of sugar to add to 1 gallon of liquid.

Here are the results In some cases I converted units, e.g. kg or oz. to lbs.

• https://fermcalc.com/FermCalcJS.html
  0.9261 lbs.
• http://www.robruark.com/other/Calculators/brewing_calculator/index.html
  0.926 lbs ( 0.42 kg)
• http://www.brsquared.org/wine/CalcInfo/HydSugAl.htm
  0.9375 lbs. (15 oz) (from table)
• https://www.vinolab.hr/calculator/chaptalisation-additions-en38
  0.866 lbs. (0.393 kg)
• https://www.brewersfriend.com/chaptalization-calculator/
  Calculation for 10 Brix (= SG 0.040)
  0.84375 lbs. (13.5 oz)

So my question is, why are these different? The calculators all refer to simply "sugar," which I take to be table sugar (sucrose).

I might need to use some distilled water and sugar to test some of these to find out which are more accurate. But it seems like that should not be necessary.

 

[winemaker81]

The discrepancies may have a technical cause, as a lot of the online calculators are written in Javascript, which is known for having problems with decimal calculations. Actually, a lot of programming languages have decimal inaccuracies, but Javascript is noted for it.

Some of the calculators are for beer, which has a lot more "stuff" in it that affects SG. I've noticed that formulas for beer often differ from those for wine, although I have not looked into the reasons for this.

For making additions to a must or wine, I've yet to find any calculation I completely trust. Nor do I trust calculators, as I don't necessarily know which formula the programmer used, and decimal handling inaccuracies are a problem.

I use 1 lb sugar = 2.25 cups, which changes the SG of 1 US gallon of water from 1.000 to 1.045. I typically add 3/4 of the amount of sugar, stir very well, then check SG. I'm not fussy about the exact SG, e.g., if my target is 1.090, 1.087 to 1.093 are sufficient.

 

[Sailor323]

I have found this chart useful. It was in the first winemaking book I ever bought. Beware, it is a British book so gallons are probably Imperial gallons.