Determining ABW without initial SG reading.

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Rocky

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From time to time I have seen posts on the forum where winemakers do not have the ISG measurement and are puzzled as to how to determine ABV. Below is a method that I found in one of my books, The Art of Winemaking by Anderson and Hull. It purports to give an accurate estimate of ABV.

1. Measure the SG of your wine, call it SG1. Measure out a known quantity of wine, say 1 cup (8 oz.), place the wine in an enameled or glass pan an d boil it down to half the original amount, i.e. 1/2 cup. All the alcohol will be out of the sample and some of the water but most of the water and all of the other components of the wine will remain.
3. Using distilled water, bring the volume of your sample back up to one cup, let it cool to the temperature of the scale of your hydrometer (usually 60 or 65 degrees F) and then take an SG reading, call it SG2. It will be higher than SG1 because you removed alcohol and replaced it with water.
4. Perform the following calculation: (SG2-SG1)x1000 = Spirit Indication and find the ABV from the following:

Spirit Indication/ABV

1.5/1.0, 2/1.3, 3/2, 4/2.7, 5/3.4, 6/4.1, 7/4.9, 8/5.6, 9/6.4, 10/7.2, 11/8.0, 12/8.8, 13/9.7, 14/10.5, 15/11.4, 16/12.3, 17/13.2, 18/14.1, 19/15.1, 20/16, 21/17, 22/18, 23/19, 24/20, 25/21, 26/22

The result will not be dead on accurate but it will give as valid an approximation as the (ISG-FSG)x131.25 method. By law, wines that we purchase in a store showing an ABV of 14% or less can vary by up to 1.5% (but can't be more than 14%). Wines showing an ABV of more than 14% can vary up to 1%. My point is, it is all an approximation.

Good luck!
 

salcoco

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We did this test a few years back in our wine club and found the accuracy is best when the sample is cooled to the hydrometer calibration temp. we measured agonist a ebuliometer got about 1 % variance
 

KCCam

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You need very accurate SG measurements. A precision hydrometer would help. FermCalc has this calculation, and if you plug in some numbers, it shows that a 0.001 error in the SG reading can make the difference between a result of 12% ABV and 13%, as an example. The table above also reflects this.
 

RichardC

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Thanks Rocky! I have a batch of pineapple wine for which I didn't take an SG reading or even FG reading. I was going to estimate the amount of sugar in the pineapple, together with the added sugar , then ratch an estimated alcohol content like in the link below. ( I would multiply by 0.85 as a fudge factor, catering for non perfect conversion and other losses)
 

KCCam

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FermCalc can do the same thing, and is geared toward fermentation. The link you provided assumes “250g sugar” means 250g glucose, and you have to account for that with a second equation. The 2 answers I saw estimated 16% and 17%. FermCalc estimates 14.3%:

250g sugar (sucrose) in enough water to make 1 L, yields an SG of 1.0957 (I know, too many sig digs). If that ferments dry to 0.990, ABV is around 14.3%.
 

KCCam

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I just downloaded the app KC! Thanks. Just to figure out how to use it. Haha
There is a lot of info on that site too if you are technically inclined at all. Most of the calculations will give results from several different methods, and the site explains the details about each. Not very useful haha, but I find stuff like that very interesting.
 
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