Adding sugar in stages, how do you calculate the ABV?

[jezbrews]

I'm a little stuck on figuring out how strong this liquor is going to be by compounding. I'm using a high alcohol yeast that can get up to at least 20%.

1kg of jaggery in 4.5l of water produces an OG of 1.092 as only 0.878kg is sugar.

After this has fermented out I'm left with 4.5l of liquor, with an FG of 1.000. Meaning of which ~12% is alcohol by volume

I then add another 1kg of sugar to put the OG back up to 1.092

Assuming this ferments out again to an FG of 1, what will the ABV be? ~24%? Some other number?

 

[dad_of_jon]

original gravity 1 - final gravity 1 - using a standard abv calculator
add more fermentables
original gravity 2 - final gravity 2 - using a standard abv calculator

add the 2 abv's together. note that you'd be near the limit of the yeast so might be pushed to get 24% as the yeast will have got fed up by then.

 

[Manners]

1kg of sugar should add 0.018 gravity points to your OG (assuming 100% fermentable).

Therefore OG+0.018 = 1.11
At new FG that equals 14.4%

Been there and had the head scratching myself! This seemed to be the most correct answer I could come up with and was ratified by others on here.

Hope that helps!

 

[Tess Tickle's Brewery]

A simple way of remembering it is:-

Add up all the spent gravity points and multiply by 135.87. That’s what I do.

Some people multiply by 131.25. But with this calculation, the higher in ABV you go, the less accurate the result is.

Just remember to take a gravity reading before and after you back-sweeten.

eg: my strawberry wine started at 1.080. When it got to 1.004 I back-sweetened. 76 points spent. After sweetening, new gravity 1.038. When ferment finished, it read 1.018. Another 20 points. So 96 points in total. 0.096 x 135.87 = 13.04%.

 

[Manners]

A simple way of remembering it is:-

Add up all the spent gravity points and multiply by 135.87. That’s what I do.

Some people multiply by 131.25. But with this calculation, the higher in ABV you go, the less accurate the result is.

Just remember to take a gravity reading before and after you back-sweeten.

eg: my strawberry wine started at 1.080. When it got to 1.004 I back-sweetened. 76 points spent. After sweetening, new gravity 1.038. When ferment finished, it read 1.018. Another 20 points. So 96 points in total. 0.096 x 135.87 = 13.04%.

Oh its on now Lisa!

I wonder who will come out victorious in the great ABV calculating methodology debate?! Genuinely interested to find out if they give similar/the same answer!

 

[Tess Tickle's Brewery]

Oh its on now Lisa!

I wonder who will come out victorious in the great ABV calculating methodology debate?! Genuinely interested to find out if they give similar/the same answer!

oh god have I started a war ha ha ha

Goodness knows which is better but as long as there’s consistency in the readings then they’re all correct

 

[johncrobinson]

Its an old chestnut,One that has great relevance to me as high alcohol fermentation's used to be my specialty.
I found the Simplest method was to keep track of the dry weight of sugar used + the initial amount in the must, this will tell you the total quantity of alcohol.All you then need to know is the total volume to arrive at the abv.
The method works because the extra sugar is fed in small doses as the gravity nears 1.000.
So any error due to unfermented sugar will be minimal.
I used to do it with pen,paper and calculator I suppose i should write a spreadsheet.

The reason i did it this way was pure laziness.It was quicker to tip a wee tub of sugar in the wine rather than fill a sample jar take reading then have to wash and sanitize all the equipment.
It also has the advantage of being able to plan the doses in advance

Tips
Add the sugar in small amounts 50-100g
wait until the yeast has eaten that before adding more (you can use a hydrometer I just watch the airlock.)

 

[Manners]

Its an old chestnut,One that has great relevance to me as high alcohol fermentation's used to be my specialty.
I found the Simplest method was to keep track of the dry weight of sugar used + the initial amount in the must, this will tell you the total quantity of alcohol.All you then need to know is the total volume to arrive at the abv.
The method works because the extra sugar is fed in small doses as the gravity nears 1.000.
So any error due to unfermented sugar will be minimal.
I used to do it with pen,paper and calculator I suppose i should write a spreadsheet.

The reason i did it this way was pure laziness.It was quicker to tip a wee tub of sugar in the wine rather than fill a sample jar take reading then have to wash and sanitize all the equipment.
It also has the advantage of being able to plan the doses in advance

Tips
Add the sugar in small amounts 50-100g
wait until the yeast has eaten that before adding more (you can use a hydrometer I just watch the airlock.)

Good advice, but what method did you use to calculate the final ABV, John?

Did you estimate the gravity points based on weight of sugar, added to OG? Did you use Lisa’s method as described above or some other black magic not yet described?

 

[johncrobinson]

Yes almost 50% of the weight of sugar is converted to alcohol.
I should of said you also need to calibrate your demijohn or fermenting vessel beforehand so you can see at a glance the total final volume.(tape or waterproof marker)

The method is not foolproof as if the fermentation stops before all the sugar is converted to alcohol there will be errors.
I used to "sugar feed" the yeast in order to get high abv so the doses were small at worst about 2oz sugar if the last lot added did not ferment so any error would be negligible.

The technically correct was as to calculate multiple gravity drops this was just a quick cheat to avoid all the hasle with the hydrometer.

 

[johncrobinson]

Whatever method is used there is a fly in the ointment.

That is when adding sugar as an inverted syrup(best way) or as honey (mead) you cant just add up the gravity points because you are adding Water as well as alcohol (as sugar).

You must keep track of the total volume,As you are now shooting at a moving target.

 

[Tess Tickle's Brewery]

Hooray so my way is technically correct!

P.S. I don't water mine down with water, I just stir the sugar in dry.

 

[Manners]

Hooray so my way is technically correct!

P.S. I don't water mine down with water, I just stir the sugar in dry.

Rofl! I didnt water mine down either! Neck and neck!

Maybe we just agree more sugar = more likely to get you pished and call it a draw!

 

[Tess Tickle's Brewery]

Rofl! I didnt water mine down either! Neck and neck!

Maybe we just agree more sugar = more likely to get you pished and call it a draw!

Sounds good to me!

 

[Harkone Silverwolf]

A simple way of remembering it is:-

Add up all the spent gravity points and multiply by 135.87. That’s what I do.

Some people multiply by 131.25. But with this calculation, the higher in ABV you go, the less accurate the result is.

Just remember to take a gravity reading before and after you back-sweeten.

eg: my strawberry wine started at 1.080. When it got to 1.004 I back-sweetened. 76 points spent. After sweetening, new gravity 1.038. When ferment finished, it read 1.018. Another 20 points. So 96 points in total. 0.096 x 135.87 = 13.04%.

Hello, I am new on here. I am making SAKE. Starting gravity was 1.140. I let it ferment down to 1.030 Then added sugar bringing the gravity up to 1.040. Fermented down to 1.020. Then added honey bringing the gravity back up to 1.040. Fermented down to 1.020 again. Have not fed any more sugar and it won't go below 1.020. Trying to figure out what the final alcohol content would be. Using your formula, Lisa, I have spent 150 points. Is that correct? Taking 150 x 135.87 = 20,380.5. That can't be the AC. Is it 20%?

 

[Tess Tickle's Brewery]

Hello, I am new on here. I am making SAKE. Starting gravity was 1.140. I let it ferment down to 1.030 Then added sugar bringing the gravity up to 1.040. Fermented down to 1.020. Then added honey bringing the gravity back up to 1.040. Fermented down to 1.020 again. Have not fed any more sugar and it won't go below 1.020. Trying to figure out what the final alcohol content would be. Using your formula, Lisa, I have spent 150 points. Is that correct? Taking 150 x 135.87 = 20,380.5. That can't be the AC. Is it 20%?

It is possible - sake can be incredibly strong. I've got the same answer as you, but with the decimal points further along. 0.150 x 135.87 = 20.3805.

Sounds like you had good yeast!

Would love for you to share your method as I haven't tried making that yet.