How to determine residual sugar content in finished cider?

[Gilligan]

What's the best way to determine sugar content of cider? All I can think of, is to evaporate or boil away a known volume of cider and weigh what's left after it dries. I'll then assume the residue is almost all sugar, with a little bit of whatever solids are left from apples and yeast. Is there a more precise and elegant way to calculate actual sugar content?

 

[VikeMan]

If you know the original and final gravities, you can get close enough for government work this way...

(OG - FG) / (OG -1) = Apparent Attenuation
Apparent Attenuation / 1.22 = Real Attenuation

Compute an "if there were no alcohol" final gravity. Call it "QuasiFG"...
((OG - 1) * (1 - Real Attenuation)) + 1 = QuasiFG

From that QuasiFG, compute the sugar per gallon...
((QuasiFG -1) x 1000) / 46.21 = Lbs Sugar Per Gallon Approximate

 

[Gilligan]

Well, I didn't record the OG... But, interesting formula nonetheless. I'll be sure to test it on my next batch. Thank you, VikeMan!

 

[Gilligan]

VikeMan, I forgot to ask earlier... What's the source of that formula you posted?

 

[VikeMan]

VikeMan, I forgot to ask earlier... What's the source of that formula you posted?

The first section (1st and second formulae) are common. Couldn't say who first identified them.

The section section ("QuasiFG") is just a quick and dirty estimate using real attenuation (instead of apparent attenuation) to get to an "FG" where the sugars are not hidden by alcohol (which is less dense than water). Don't know if this formula has ever been used exactly this way before.

The thirds section takes a constant of 46.21 "points per pound per gallon" for sugar to convert the "QuasiFG" to sugar pounds per gallon. Algebraically, it's equivalent to a standard formula for computing wort gravity given the pounds per gallon of sugar, just used in reverse.

 

[Vale71]

What's the best way to determine sugar content of cider? All I can think of, is to evaporate or boil away a known volume of cider and weigh what's left after it dries. I'll then assume the residue is almost all sugar, with a little bit of whatever solids are left from apples and yeast. Is there a more precise and elegant way to calculate actual sugar content?

Actually there is but it involves the use of somewhat expensive chemicals and gear, so it's basically out of reach of most homebrewers/cider/winemakers.

This is the oldest and probably the simplest method:

http://blamp.sites.truman.edu/files/2016/01/Fehling-final.pdf