Testing for Residual sugar in a wine

One of my wine making friends was talking about his 2009 Sauvignon Blanc and how it tasted a little sweet. He was wondering about how much residual sugar was left in the wine and if it would be stable in the bottle.

Two wine making sayings came to mind when talking about this topic: If you taste sugar in the wine, there is usually more than 1% there since that is about the normal tasters threshold for sugar, and if you want to re-start a stuck fermentation, just bottle the wine! { wine with residual sugar will very likely ferment in the bottle, that's how sparkling wine is made!}

So it's better to know if the wine has residual sugar before bottling.

If you like the taste of the wine with a little residual sugar you may need to take some steps to make sure the wine does not kick off a fermentation in the bottle. Of course a few bubbles in a Rose is not necessarily a bad thing to happen... but not in a white wine that you are proud of...also a fermentation in the bottle can lead to cloudy wine and off odors.

You cannot use the hydrometer to measure sugar once fermentation is done since the alcohol is lighter than water and that's what the hydrometer is measuring; the specific gravity {SG} of the solution against the SG of water {1.0}. When there is more then 10% alcohol and only a few brix of sugar you can get a negative number reading on the hydrometer.

e.g. 1 brix = .00388 SG. So a wine with 6 brix of sugar will have a SG reading of approx. 1.023 not counting the alcohol!

If we take into account the @ 10% alcohol which has a SG of @ .78 the resulting SG reading should be: ( .88 * 1.023 + .10 * .78 = .9782) a negative number!

One method I use to measure residual sugar is to use a Urine sugar test kit. The kit is very easy to use and will measure sugar in the range : negative sugar up to more than 4%.

I purchased my "kit" years ago. It's called Clinitest Urine sugar test kit. It consists of a small test tube, a eye dropper, reagent tables, and a color chart for reading the results.

I don't think you can buy the kit any longer, but the reagent tablets are still available so you can put together your own kit.

A friend that is a nurse said they {hospitals} don't use the tablets anymore and the reagent tablets are inventory that is being sold off.... Amazon carries them...

Clinitest Reagent Tablets

Add you own test tube and eye dropper and you will be set for measuring residual sugar in your wines.

Note that there are residual sugar testing kits available from wine making supply stores. One kit available is the Accuvin Residual Sugar Test Kit.

One reason I like the urine sugar kit more than the Accuvin kit is that the test strip colors are very bright and easy to read...e.g. they are not all some shade of blue as in the Accuvin kit....

Here's a video of me measuring residual sugar in a few of my wines.