Off the wall about ABV and SG

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Scooter68

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I understand that there is really no way to accurately measure the ABV of a wine without sophisticated lab tests but just wondering.

Since pure water's expected SG is 1.000 and pure ethyl alcohol has an SG of .789 can any sort of formula be used to estimate the ABV, post fermentation. Other than comparing Startiing SG and Final SG and calulcating. Granted that the other elements in a wine will taint any direct calculation is there any sort of approximation that could be done base purely off final SG assuming all sugar has fermented out?

I ask because if I start with an SG of 1.1100 and ferment all the way to "dry" the lowest SG likely I hear mentioned is .990 but; if I start with an SG of 1.070 and ferment all the way to "dry" I also expect to get an SG of .990 so it seems that there is a total disconnect from ABV to SG once you hit 1.000.

Maybe another way to say this is - If I make a 50/50 mix of pure ethyl alcohol and pure water would my SG then be .894 ?

As I said just an off the wall question. (Maybe the heat has gotten to me, again.) :d
 
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From what I've read, the other constituents in wine are enough of a variable that we (home winemakers) will never calculate a truly accurate ABV. There are at least 3 equations that approximate the ABV, which depend on the ABV (e.g., if the ABV is 10%-14%, use equation 2 ...).

I calculate my ABV to 1 decimal point and am consciously oblivious to the fact that my calculation is almost certainly wrong. :p
 

sour_grapes

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Maybe another way to say this is - If I make a 50/50 mix of pure ethyl alcohol and pure water would my SG then be .894 ?

Believe it or not, the answer to this question is "no." When you mix water and ethanol, volume is not conserved. That is, if you add 1 L water, and 1 L ethanol, you wind up with LESS than 2 L of liquid. So the SG would be higher than the average of the constituents.
 

Scooter68

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Thanks. I consider the subject "closed"

I think if I had taken the time to look at the numbers and realize how fine a dfference there is, even without consdering both the points you all made, I would have said - Yeah we can't measure to that level with standard home wine making equipment.
 
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