Calculating ABV if water / sugar added part way through

Discussion in 'Tutorials, Calculators, Wine Logs & Yeast Charts' started by Toonster, Jan 5, 2018.

  1. Toonster

    Toonster Member

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    Hi,

    Apologies if this has already been asked/answered before - the advert at the top of the page is overlapping the search box meaning that I can't search the forums!

    Is there a simple way of calculating the final alcohol percentage if I have added water part way through the process? I'm currently making Elderflower wine, and the recipe I was following got me to top up with water after the first racking.

    I started with an SG of 1.152 (9 litres of water), and yeast added at this point. At the first racking, it was 1.100. 8 litres of water then added, making the SG 1.040. When fermentation fully ceased, and after the next racking, it was at 0.90.

    I've not the foggiest where to start with this - there'd obviously be some alcohol in there from the first fermentation, but I've then diluted it. This is only the fourth batch of wine that I've made, and the first where I've 'tinkered' with the wine part way through!

    Many thanks in advance.
     
  2. sour_grapes

    sour_grapes Victim of the Invasion of the Avatar Snatchers

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    We could go a couple of ways, here.

    When you went from 1.152 to 1.100, your SG fell 0.052, which would imply an ABV of 0.052*131= 6.8% ABV. Now, let's think about how much ethanol that is. It is 9 liters*0.068 = 0.61 liters. Next, you added 8 liters of water (but still have 0.61 liters ethanol), so your ABV is now 0.61/(9+8)= 3.6% ABV. Now, you fermented your SG from 1.040 to (I am assuming) 0.990. (There is essentially no way to get to 0.900, so I suspect you meant 0.990.) This gives a further amount of alcohol equivalent to (1.040-0.990)*131= 6.5%. Thus, your total will be 3.6% + 6.5% = 10.1%.

    Note that I am taking you on your word that adding 8 liters of water to a 9-liter solution at 1.100 results in 1.040. Doesn't seem quite right to me. FermCalc (http://web2.airmail.net/sgross/fermcalc/fermcalc_applet.html) suggests it would be more like 1.053. If that figure is correct, you would get more like 11.8% for a final value. Such a figure is more consistent with the other way to estimate this, which would be to pretend that you fermented the initial 1.152 down to 0.990, for a (fictitious) 21.22 ABV, which you then diluted by a factor of 9/(9+8), giving 11.2 ABV.
     
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  3. Toonster

    Toonster Member

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    Thank you so much! Both calculation routes sound very logical :)

    It is highly likely that I've either mis-written down, or (more probable!) mis-read my hydrometer. I've been having some definite user-error type issues with it; same with my vino-o-meter, which has been consistently giving me 20-25% with any of my homebrews...
     
  4. sour_grapes

    sour_grapes Victim of the Invasion of the Avatar Snatchers

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    You are welcome!

    Vineometers are "for amusement purposes only"!
     
  5. Toonster

    Toonster Member

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    I sort of noticed that - a friend recommended it to me, but I'm not really sure it is of any use apart from to look pretty...
     

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