Specific gravity question

[iridium]

So I have been making wine for a little over a year now and have a question regarding the relationship between specific gravity and alcohol percentages.

I know that by measuring the original specific gravity and the final specific gravity of a wine you can use the difference to calculate a approximate alcohol by volume amount.

What I don’t understand is how backsweetening lowers an abv amount. In my research specific gravity actually measures the density of a liquid. So in fermentation you change the density of the liquid because the yeast are converting sugar to alcohol.

When you backsweeten you add back sugar so you get a higher specific gravity reading. Assume that you have added potassium sorbate to prevent further fermentation for this question. Also assume that the amount of additional volume is minimal because sugar was added directly to the wine rather than in a simple syrup.

Given that you have not added any volume you should not have changed the alcohol by volume amount. Is that correct? If it is correct the. Why do many say the ferment to X% and then back sweeten to a lesser percent when they have not added any additional volume to dilute the alcohol.

Thank you for clearing this up for me.
Iridium

 

[GreenEnvy22]

Adding sugar won't lessen the amount of alcohol in any meaningful way. It will drop a tiny bit as you're essentially diluting the wine, but probably not measurable. If you're adding a syrup, it may be measurable as there is more mass (at 0% alcohol) going in. Still will be a small amount.
It certainly can reduce the the "taste" of alcohol, giving the impression there is less alcohol in the wine than there is, but it's just making the alcohol, it's still there.

 

[meadmaker1]

Ferment to X so that fermentation stops. Sorbate and k meta only prevent restarting
Many back sweeten with syrup so volume is increased, i often sweeten or boost flavor with juice or juice concentrate. I try to anticipate and raise sg in the begining but focus more on taste than maintaining abv

 

[richmke]

> Why do many say the ferment to X% and then back sweeten to a lesser percent when they have not added any additional volume to dilute the alcohol.

You don't ferment to x%. You ferment to completion, and the difference between starting and ending SG gives you an estimate of ABV. Then you back sweeten.

Why not do the calculation up front, and start with a higher SG, and end at, say 1.02, to give you x%: Because you can't (unless you are making a dessert wine).

Keith alluded to it. It is very difficult to purposefully stop an active fermentation. So, it is easier to: 1) let it finish by itself (fully ferment); 2) rack to remove the sediment; 3) add k-meta to kill what you can; 4) Repeat 2 and 3 for a few months; 5) Then, add sorbate and back sweeten. Stop short of the sweetness you want. Sample a few weeks later. Add more sugar as desired (sorbate only needs to be added once). Repeat adding sugar until you are happy. Repeat 2 and 3 until you are ready to bottle.

 

[iridium]

Thank you all. This confirmed what I though about fermentation specific gravity and abv