I found a formula on the net that uses SG and Brix for finished wine. Not absolutely accurate, but close enough for comparison of personal production.
Tools needed, hydrometer and refractometer.
( brix x 4 ) + 1000, -SG. divide by 3.3 = ABV
Sample: loquat wine, sg 998, brix 7.5
So, 7.5x4=30, plus 1000= 1030, -998= 32, divide by 3.3= 9.7, so call it 10% Stabilize and add a bit more sugar, I like 10/10 wine- 10% sugar, 10% abv.
Original formula went through too many steps of dividing by ever smaller numbers, out to 5 or 6 decimal places. I don't think I need to know that the loquat wine above is actually 9.6969696969 abv. And how accurate are your instruments, at what temp? So I simplified, then tested several commercial samples of wine, compared to the label. As I recall, about +/- 1/2%. Close enough for a home brewer.
The potential alcohol as listed on the side of the hydrometer scale won't work for wines made from must, too much unfermentable junk in the wine to trust the OG.
For not-must concoctions, I use the change in the refractometer brix reading, before and after, divide by 2 to get abw, times 1.21 to get abv.
Hope this helps, feedback would be appreciated- try it on some commercial stuff?
REALLY sorry to necro a thread but i've been really confused by this lately. and would rather that than start a duplicate
Here are my numbers for the batch I'll use as an example.
The OG was 1.045, and then i added sugar, bringing OG = 1.060
From 1.060 on the hydrometer, i can look to the balling (brix) scale and see that this gravity would give me a reading of 15, and a potential alcohol of just shy of 8%. The final gravity of this cider was 0.999.
Now, using the above brix equation gives me:
( 15 x 4 ) + 1000, - 999. divide by 3.3 = ABV = 18.49%
BUT using the hydrometer's (admittedly imprecise) scale of potential alcohol, i can only possibly have less than half that.
Going back to the usual calculation using the gravities,
(OG-FG) x (F) = ABV%
As OP Said, there are a bunch of F's i've found, but this seems to be the most
reputable. If i use the F given by that site, I end up with the following:
(1060-999) x (0.132) = 8.05 which seems like it makes sense.
I guess my question is, why doesnt the brix equation work, and should i be using these F's every time i do a calculation instead of choosing somebody's constant since everyone seems to use something different? If so, I'll definitely be copying that table into my notebook.
edit: also, it says "
f is the factor connecting the change in gravity to alcoholic strength. The value of 'f' is not constant because the yield of alcohol is not constant for all fermentations. In lower strength beers, more of the 'sugars' available for fermentation are consumed in yeast reproduction than in producing alcohol."
So, my question then becomes wouldnt the factor change also depending on how much yeast i pitch into the must, doesnt adding more yeast cells off the bat reduce the need (at least a little bit) for the yeast to reproduce, or am i just really really overthinking this.