# Calculation of residual sugar as a "percentage"?



## BernardSmith (Jun 10, 2015)

Just curious: I came across a reference to a mead that specified the amount of residual sugar (and hence sweetness) as a percentage (eg 2 percent). How is that calculated? And is this calculated in terms of the original specific gravity or the original gravity less final gravity? or what? Thanks


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## sour_grapes (Jun 10, 2015)

As far as I know, Brix is just a measure of the percentage (by mass) of sugar in the solution. So 2% is 2 Brix. You can easily find tables to convert Brix to SG, like this one: http://www.winning-homebrew.com/specific-gravity-to-brix.html


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## BernardSmith (Jun 10, 2015)

Aha! Thanks Paul. Your point makes some sense. Rule of thumb (I think) is that 1 Brix = 4 gravity points (1.004) so 2% would be about 8 points. But I thought that Brix was a measure of sugar in the fruit itself ,prior to fermentation, and not after. But here's the problem: If the final gravity is .990 and I add enough sugar to bring the gravity up to .998 then the Brix would be zero and not 2%, so I guess folk must be using some other measure


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## wineforfun (Jun 10, 2015)

BernardSmith said:


> Aha! Thanks Paul. Your point makes some sense. Rule of thumb (I think) is that 1 Brix = 4 gravity points (1.004) so 2% would be about 8 points. But I thought that Brix was a measure of sugar in the fruit itself ,prior to fermentation, and not after. But here's the problem: If the final gravity is .990 and I add enough sugar to bring the gravity up to .998 then the Brix would be zero and not 2%, so I guess folk must be using some other measure



I have always been curious about this too Bernard. 

I have drank a Chateau Ste. Michele gewurztraminer that has 1.6g/100ml residual sugar.
I assumed it stopped short of running completely dry(less than 1.000) and retained some of the original grape sugar from the start of fermentation.
With that said, I too, would like to know how they calculate this.


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## Runningwolf (Jun 10, 2015)

one brix is one percent and five brix is 5 percent. If you stop your fermentation at 3 brix you have 3 percent as long as the fermentation really did stop. If I ferment dry and add 3 percent sugar then that is what it is.


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## BernardSmith (Jun 10, 2015)

Thanks Dan. So it _really_ is as simple as it seems.. .


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## sour_grapes (Jun 10, 2015)

Perhaps a possible source of confusion is the SG <=> Brix table I posted. It is ONLY accurate when there is no alcohol involved, i.e., pre-fermentation.


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## seth8530 (Jun 10, 2015)

wineforfun said:


> I have always been curious about this too Bernard.
> 
> I have drank a Chateau Ste. Michele gewurztraminer that has 1.6g/100ml residual sugar.
> I assumed it stopped short of running completely dry(less than 1.000) and retained some of the original grape sugar from the start of fermentation.
> With that said, I too, would like to know how they calculate this.



1.6 g/100 ml is about the same as 1.6 brix. Ie, you have 1.6grams of sugar for roughly every 100 grams of water. Thus the mass fraction is .016, and if you multiply by 100 you get 1.6 brix which is mass sugar over mass solute.


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## GreginND (Jun 10, 2015)

In a finished wine it is not the brix you measure with a hydrometer because of the alcohol changing the density. It is grams of sugar per 100 mL of wine.


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## seth8530 (Jun 11, 2015)

GreginND said:


> In a finished wine it is not the brix you measure with a hydrometer because of the alcohol changing the density. It is grams of sugar per 100 mL of wine.



And how do you measure that?


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## GreginND (Jun 11, 2015)

Well, the concentration can be analyzed by a lab but I do it by adding sugar to dry wine. Grams per liter volume.


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## wineforfun (Jun 11, 2015)

GreginND said:


> Well, the concentration can be analyzed by a lab but I do it by adding sugar to dry wine. Grams per liter volume.




Greg,
Help me out here then.
Let's say you run a wine dry, to .994. Then add sugar to bring it to 1.010. What would the residual sugar be or can you calculate it from the above?
Thanks.

I may be overthinking it, as I usually do, but by definition, residual means leftover or remaining. I take that as meaning the sugar left after fermentation, not adding it back in.
Now maybe the term residual is not meant to be used literally, as I am doing.


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## GreginND (Jun 11, 2015)

Well, traditionally RS is the sugar left after fermentation if it wasn't taken to dryness. But now it is the percent sugar in the wine whether added after the fact or left from fermentation. Most wineries add sugar after the fact. 

To calculate your percent you need to know the weight of sugar added and the final volume (in liters). If you are just adding back to a certain SG without weighing the amount of sugar you added, it's harder to estimate based on the gravity alone due to the change in density from the alcohol. Perhaps a good estimate is the total change in SG from 1.010 - 0.994 then converted to brix (%).

Some useful relationships:
1 g per liter = 1.0% sugar
3.79 g per gallon = 1.0% sugar
0.13 oz per gallon = 1.0% sugar


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## seth8530 (Jun 11, 2015)

GreginND said:


> Well, traditionally RS is the sugar left after fermentation if it wasn't taken to dryness. But now it is the percent sugar in the wine whether added after the fact or left from fermentation. Most wineries add sugar after the fact.
> 
> To calculate your percent you need to know the weight of sugar added and the final volume (in liters). If you are just adding back to a certain SG without weighing the amount of sugar you added, it's harder to estimate based on the gravity alone due to the change in density from the alcohol. Perhaps a good estimate is the total change in SG from 1.010 - 0.994 then converted to brix (%).
> 
> ...



Not to nitpick, but I think you missed a 0, atleast on 1g per liter=1%sugar.

Ie, 1gSugar/1000gWater =.001 Multiply that by 100 and you get .1%.

I would agree with greg though, if you are at home and you want to ESTIMATE the sugar concentration, you would need to start off with something that is considered dry ie, close .992 ish and then state that all the sugar that is in their is by virtue of me adding it in.

And thus, take the mass of sugar you add in their in grams and divide that by the volume in liters divided by 10 to get the brix. Or you could do it by volume in ml and multiply by 100 and get the same answer.


The reason why this works is because 1g of water is very close to 1 ml of water.


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## sour_grapes (Jun 11, 2015)

GreginND said:


> Some useful relationships:
> 1 g per liter = 1.0% sugar
> 3.79 g per gallon = 1.0% sugar
> 0.13 oz per gallon = 1.0% sugar



Greg, shouldn't that be

"10 g/l = 1.0% sugar" ?


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## sour_grapes (Jun 11, 2015)

wineforfun said:


> Greg,
> Help me out here then.
> Let's say you run a wine dry, to .994. Then add sugar to bring it to 1.010. What would the residual sugar be or can you calculate it from the above?



You can probably use a rule of thumb, but you could also use Fermcalc. It has a mode where you can specify your starting SG, your initial volume, and your ending SG, and it will tell you how much sugar you had to add and your final volume. In the case you asked about, you would have to add about 41 g of sugar to 1 liter, so that example corresponds to about 4.1% residual sugar. (And, yes, don't take the "residual" literally.)


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## wineforfun (Jun 11, 2015)

Making more sense now. Thanks guys.


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## GreginND (Jun 11, 2015)

Sorry - everything was off by an order of magnitude. Forgive me. It's been an emotional day - military honors for my father's service and seeing family I haven't seen in decades. Bittersweet and all good. But I'm emotionally exhausted.


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## sour_grapes (Jun 11, 2015)

GreginND said:


> Sorry - everything was off by an order of magnitude. Forgive me. It's been an emotional day - military honors for my father's service and seeing family I haven't seen in decades. Bittersweet and all good. But I'm emotionally exhausted.



Condolences on your loss, Greg. Peace, my friend.


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## vernsgal (Jun 12, 2015)

I like to read these math ones and don't usually comment because honestly I'm usually more lost than found .
I just wanted to give my condolences to you Greg.
Sorry for your loss


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## Runningwolf (Jun 12, 2015)

Sorry for your loss Greg.


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## BernardSmith (Jun 12, 2015)

My condolences too, Greg. So sorry to hear of your loss.


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