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1. Drop the hydrometer into your wine before fermentation. Once the hydrometer has settled and is floating, record where the surface of the liquid crosses the gravity scale.

2. Place the hydrometer in your wine at the end of fermentation and record the specific gravity. The reading will be different, because as yeast metabolizes sugar, it produces ethanol and carbon dioxide. The carbon dioxide is released and the liquid that is left behind become less heavy.

3. Calculate the amount of alcohol in the wine by using this formula.

Percentage of alcohol = ((1.05 x (OG - TG)) / TG) / 0.79

OG is the original gravity reading that you took. TG stands for terminal gravity or the reading you took at the end of fermentation.

For example, if the original gravity was 1.06 and the terminal gravity 1.01, the equation would read:

Percent alcohol = ((1.05 x (1.06 - 1.01))/1.01) / 0.79

Therefore, the wine's alcohol percentage is 6.6.

There's also a calculator found on this page.

Alcohol Content by the Boiling (Spirit-Indication) Method

This method was first proposed by M. E. Tabarié in 1830 as a simplified alternative to the distillation procedure. It is based on the principle that alcohol causes the same depression in specific gravity in wine as it does in pure water.

The method involves evaporating (boiling off) a portion of the wine sample until all of the alcohol is evaporated, and then replacing the evaporated volume with distilled water. The difference between the specific gravities of the wine and the volume-corrected residue are then used to estimate the specific gravity of the distillate, which represents the specific gravity of a pure water/ethanol mixture, from which the alcohol content can be estimated. The experimental procedure is summarized below.

- Measure the specific gravity (
*sgw*) of the wine to be tested. - Take a sample of about 250-500 mL (1-2 cups) of the wine and boil the sample down to approximately half of its original volume to drive off all of the alcohol.
- Allow the boiled residue to cool to room temperature.
- Add distilled water to the residue until the total volume is restored to the original sample volume.
- Measure the specific gravity of this volume-corrected residue
*sgr*, which will be greater than*sgw*because the alcohol has been replaced by water.

In addition to estimating the alcohol content, we can also calculate the solids content (true Brix) of the wine from the specific gravity of the volume-corrected residue. First we just need to convert the residue specific gravity measurement to a Brix value by using the

where