How to Measure Residual Sugar?

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bkisel

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Is there a simple way to measure residual sugar? Maybe with just a hydrometer? Wouldn't the measurement be of the sugar left after fermentation PLUS any sugar from back sweetening?

[The Wine Entry Form for the up coming Canton Wine and Cheese Festival requires the % Residual Sugar be listed. FYI... "12. The categories for judging are Dry/Semi-Dry (Less than 3% residual sugar) and
Sweet/Dessert (3.1% or more residual sugars.)"]

Thanks...
 
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Deezil

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If I remember right, it's roughly the Brix measurement

5 Brix = 5% residual sugar = ~50 grams sugar/liter

It's not exact, because ABV plays a role too - but for the life of me, I can't find the formula that takes ABV into consideration
And my brain is fried from college, so I can't piece it together myself at the moment
 

bkisel

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That should be close enough. So find my final SG, after any back sweetening, then rotate the hydrometer and read the Brix.

Thanks...
 

NorCal

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Not sure it is even that complicated and sure there will be some margin of error due to the % alcohol, but drop the hydrometer in the must and read the brix add some sugar and stir, the brix will rise and be immediately evident. It is easier with precision hydrometers; I have one that goes from -5 to 5 brix, so it is pretty accurate.
 

richmke

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> Wouldn't the measurement be of the sugar left after fermentation PLUS any
> sugar from back sweetening?

How do you propose the measure the "sugar left after fermentation"?

The measurements from a Refractometer and a Hydrometer presumes the absence of alcohol. Once fermentation starts, you need to know the original SG in order to estimate the current alcohol level in order to adjust the reading to get the current sugar level. If you add sugar along the way, that makes the adjustment even more complicated.

> The Wine Entry Form for the up coming Canton Wine and Cheese Festival requires
> the % Residual Sugar be listed.

Assuming that you are not on the edge of one category, your can "estimate" the residual sugar from the SG.

Assume that 0.992 SG is 0% sugar. Current SG - 0.992 = approximate residual sugar level. If you are 2.5% or lower, or 3.5% or higher, then you should be fine. If you are right on the edge of 3.0%, then you might need a more refined analysis.
 
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Runningwolf

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Use a clinitest to measure sugar
 

Johny99

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Yup, clinitest

Use a clinitest to measure sugar
I agree. The physics of a hydrometer with anything other than pure water get very complicated. Not worth the effort between alcohol, and remember there are different ones, solids, temperature, and other density changing stuff. A clinitest is cheap reliable and if you are careful, pretty accurate. The alternative is a test lab. The one here is like $40 bucks for a pretty complete panel. Sure adds to the cost of entry tho!
 

bkisel

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I agree. The physics of a hydrometer with anything other than pure water get very complicated. Not worth the effort between alcohol, and remember there are different ones, solids, temperature, and other density changing stuff. A clinitest is cheap reliable and if you are careful, pretty accurate. The alternative is a test lab. The one here is like $40 bucks for a pretty complete panel. Sure adds to the cost of entry tho!
This is beginning to bother me. Not the responses themselves to my question but the feeling I'm getting that it's just not worth going through the hassle to enter a bottle of my wine into this amateur wine contest.
 

Deezil

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If you're not messing with the Feds, a hydrometer should work just fine.

This isn't rocket science, and it's not gonna blow up if you're off by a few points either way

Use the Brix measurement for anything non-commercial
Use a Clinitest tablet if you wanna be 'spot on'
 

NorCal

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This is beginning to bother me. Not the responses themselves to my question but the feeling I'm getting that it's just not worth going through the hassle to enter a bottle of my wine into this amateur wine contest.
Everyone else entering is in the same boat as you, but probably haven't thought through it as much as you.
 

we5inelgr

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Resurrecting this thread as it seems Clinitest is discontinued again. Any alternatives to it?
 

we5inelgr

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Since Clinitest was discontinued by the manufacturer (Bayer), AimTab Tablets are a current alternative sold at the Vintner's Vault for 36 tabs/$38.99.

Another source, Medixcorp has the AimTab's at 36 tabs/$26.75.

Use the same procedure & color chart as Clinitest.

Note: There are other testing tablets made by the Germaine manufacturer (ex. Keytone test tablets) with packaging that looks identical.
When ordering, make sure your getting their 'AimTab Reducing Substances Tablets' for testing sugars (Glucose, Lactose, Fructose, Galactose).
 
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winemanden

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If you boil off the alcohol then take a hydrometer reading, wouldn't that give you the residual sugar?
 

we5inelgr

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If you boil off the alcohol then take a hydrometer reading, wouldn't that give you the residual sugar?
It's an interesting question. I would wonder, though, how you would know when all the alcohol is boiled off? Or, if you are boiling off any other volatile liquids.
 

sour_grapes

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Alcohol boils at 173 degrees, water 212.
Of course, it is not as simple as that. The boiling point of a pure liquid is determined by the strength of the interaction between its constituent molecules. For a solution of ethanol and water, the water molecules interact with both other water molecules and ethanol molecules, and same for the ethanol molecules. The result is that the vapor coming off is a mixture of alcohol and water. It is true that, for ABV values typical of wine, the vapor coming off is richer in ethanol than in water.

Here are a couple of good sources to discuss some of these concepts: https://en.wikipedia.org/wiki/Azeotrope

https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Physical_Equilibria/Fractional_Distillation_of_Non-ideal_Mixtures_(Azeotropes)

 

we5inelgr

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yes, that was my concern regarding simply trying to "boil off the OH" from wine and use that as a means to determine residual sugar.

there are many volatile compounds in wine and they all don't boil at the same temperature. not to mention, the expensive means to measure that (IR spectroscopy or even gas chromatography).
 
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