is it possible to increase abv at end of fermentation?

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Eric Bertoldo

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Hi friends. I am nearing the end of fermentation with a Zinfandel kit with skins. I've been making wine for aprox 4 years and I made a rookie mistake of not doing the math when I took my initial reading. I started out at 1.082. Im nearing the end (14 days as of this post) with a .996 s.g. I was hoping, being a zin, that I would end up at around 14-15 abv. But I guess by not doing the calculations that I could just sprinkle fairy dust on it and it would magically be what I wanted. I should have added a little sugar to get it there, but I didn't.
My question is, has anyone ever added some sugar at the end to increase the abv? and if so, what would be the formula for figuring the abv when I'm done?
Im ok with letting it be what it is. I would hate to ruin it. But I'm just a little disappointed in the low abv which seems to be aiming at around 11.3 to 12.1. I now some will say why do I need higher abv? ...... Just a personal preference.
Thanks all.
 

Ohio Bob

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You should be able to know the ABV given the SG, my hydrometer I think has a scale right next to SG which reads potential ABV. From your calculations you would also know how much sugar you shorted the juice, I think. So it should be possible to add sugar while it’s still fermenting to get back to a reasonable ABV. Or at least if you think the yeast is still capable of fermenting new sugars.

If that doesn’t work another approach is to ferment it dry to whatever ABV you get that corresponds to the SG of 1.082, then use the Pearson Square spreadsheet to fortify your wine from ~12% to 15%. Everclear 190 is the fortifying spirit of choice but 150 will also do. This approach might be preferred if you like the taste of your wine now, but not not the low ABV.
 

Rice_Guy

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1.082 gravity in grape juice should have 24% sugar
for 15% ABV you want a little over 35% sugar 14% about 32% sugar
for your target alcohol you could add roughly 8% sugar

i have not intentionally done what you want to do, however I have added sugar to back sweeten six month old wine and had active yeast which surprised me when they carbonated the wine, most of us kinda know that adding sugar risks more fermentation.
BUT, ,,, your yeast cell count has started to slow down so I would look up the technique of step feeding, adding first a one percent increase, waiting a day to see that the yeast is taking it then the second percent with waiting again then third etc. this reduces the risk of shocking the yeast and creating a very sweet stuck fermentation. Even with step feeding you could see the yeast crater so measure to watch the change.
. I started out at 1.082.
need around 14-15 abv.
and ,,, welcome to Wine Making Talk
 
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Eric Bertoldo

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You should be able to know the ABV given the SG, my hydrometer I think has a scale right next to SG which reads potential ABV. From your calculations you would also know how much sugar you shorted the juice, I think. So it should be possible to add sugar while it’s still fermenting to get back to a reasonable ABV. Or at least if you think the yeast is still capable of fermenting new sugars.

If that doesn’t work another approach is to ferment it dry to whatever ABV you get that corresponds to the SG of 1.082, then use the Pearson Square spreadsheet to fortify your wine from ~12% to 15%. Everclear 190 is the fortifying spirit of choice but 150 will also do. This approach might be preferred if you like the taste of your wine now, but not not the low ABV.
Thank you. I appreciate the feedback. I'm glad to see that there still might be some hope. :) I'll give it a try and will post my results. Thanks again.
 

Eric Bertoldo

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1.082 gravity in grape juice should have 24% sugar
for 15% ABV you want a little over 35% sugar 14% about 32% sugar
for your target alcohol you could add roughly 8% sugar

i have not intentionally done what you want to do, however I have added sugar to back sweeten six month old wine and had active yeast which surprised me when they carbonated the wine, most of us kinda know that adding sugar risks more fermentation.
BUT, ,,, your yeast cell count has started to slow down so I would look up the technique of step feeding, adding as one a one percent increase, waiting a day to see that the yeast is taking it then the second percent with waiting again then third etc. this reduces the risk of shocking the yeast and creating a very sweet stuck fermentation. Even with step feeding you could see the yeast crater so measure to watch the change.

and ,,, welcome to Wine Making Talk
Thank you. I like your idea of step feeding. Ill research this technique and give it a try. I always knew my teachers where right and I would need to use math in my life at some point. lol. We'll see how it goes. Thanks again.
 

Eric Bertoldo

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You should be out on Pine Island Sound in the middle of a thunderstorm blowing in from the gulf while kayak fishing. 😕 at least it’s usually warm.
Welcome to WMT
No Thanks ! lol ! That sounds crazy. Is that Florida? Winds have been averaging around 15-20 here. At least on my days off..... go figure. :)
 

Eric Bertoldo

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So, my s.g yesterday was .996, I told myself if it was lower this morning, indicating the yeast was still active I would attempt to step feed with a little sugar. It was .992 as of 7am. I added 1 pound of sugar ( hope that wasn't to big of a step for 6 gallons?) But according to my calculations, that would increase it about .08 abv. We'll see.....
 

sour_grapes

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So, my s.g yesterday was .996, I told myself if it was lower this morning, indicating the yeast was still active I would attempt to step feed with a little sugar. It was .992 as of 7am. I added 1 pound of sugar ( hope that wasn't to big of a step for 6 gallons?) But according to my calculations, that would increase it about .08 abv. We'll see.....

I think you meant 0.008 increase in SG?
 
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