How is the ABV on a bottle of wine calculated?

There are a couple of ways in which the ABV or alcohol by volume in wine is calculated. While traditional methods involved distillation and measuring the specific gravity of the distillate, modern winemaking practices utilise specific gravity readings of the fermenting must and calculating the ABV based on the difference in specific gravity measurements.

1. Calculation from Specific Gravity:

- Obtain a sample of the wine before fermentation begins and measure its specific gravity using a hydrometer or a refractometer. This is known as the "original gravity" or "starting gravity".

- After fermentation is complete, take another specific gravity measurement of the wine. This is called the "final gravity" or "ending gravity".

- The difference between the original gravity and the final gravity is known as the "attenuation". This difference is proportional to the amount of sugar that has been converted into alcohol during fermentation.

- The ABV can be calculated using a formula that takes into account the starting gravity, final gravity, and a few other factors. The formula is:

```

ABV (% v/v) = (Original Gravity - Final Gravity) * 131.25

```

For example, if the original gravity of the wine was 1.080 and the final gravity was 1.000, the ABV would be:

```

ABV (% v/v) = (1.080 - 1.000) * 131.25 = 10.53%

```

2. Gas Chromatography:

- In some modern wineries, gas chromatography is used to directly measure the amount of alcohol in the wine. This method involves injecting a sample of wine into a gas chromatograph, which separates the different components of the wine based on their boiling points. The amount of alcohol in the wine can then be determined by measuring the peak corresponding to alcohol.

It is important to note that ABV measurements can be affected by various factors such as temperature, dissolved solids, and the presence of residual sugar in the wine. Accurate measurement of ABV is essential for labelling, pricing, and complying with legal regulations in different regions and countries.