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How to Calculate Alcohol By Volume?

While alcohol has always been a part and parcel in our celebrations, it is always wise to be under check and avoid the unnecessary influence of alcohol by over-consumption. One of the realist ways to be in check is calculating the alcohol by volume so that you can curb the consumption and usage. 

The Process:

The term alcohol by volume is a globally accepted terminology for the measurement of ethanol in a given alcoholic beverage, this is generally expressed as volume percentage. The standard way of assessing it is by calculating the amount in milliliters of the pure ethanol in a solution of 100 ml at 20°C (68°F). The amount of ethanol in its pure form is divided by the density of it ( at 20’ C) which accounts for 0.789 g/mL.

1. Calculating ABV from specific gravity-

The standard method of calculating ABV is to use the ‘specific gravity’. Specific gravity is the relative density of a liquid compared with the density of water. When fermentation takes place, the specific gravity of the liquid is subject to change. One can monitor this change to find the alcohol content.

The most recent formula was presented by Cutaia, Reid, and Speers in 2009. The first formula from their research relates to the measurements of the alcohol content by weight with the original and apparent extract:

ABW =(0.372 + 0.00357 * OE) * (OE – AE)

where:

  • ABW is the alcohol by weight, measured in percents
  • OE is the original extract (before fermentation), measured in Plato degrees.
  • AE is the apparent extract (after fermentation)

From the above formula, an equation for alcohol by volume was derived:

ABV = ABW * (1.308 * 10-5 + 3.868 * 10-3 * AE + 1.275 * 10-5 * AE2 + 6.3 * 10-8 * AE3 + 1) / 0.7907

One can determine the volume of alcohol in a 500 ml bottle of 4.5% beer. If you are interested in finding this value, use this equation:

Alcohol Volume = Total volume * ABV

Note: All formulas for finding the ABV are approximate, as they are found empirically rather than derived. 

If the above formula to calculate ABV seems overwhelming, you can use an Alcohol by Volume calculator online to get the results.

2. Practical Estimation:

In case if you are not up for the intricate calculation, you can simply go ahead with the practical estimation. In the process of production of wine and beer, yeast is added to a solution of sugar. As the function of the yeat is concerned it acts on the sugar and produces alcohol. Talking in the general science terms the density of sugar in water is more than that of alcohol in water. Using a hydrometer, one can easily measure the changes in the specific gravity of the prospect solution before and after the addition of yeast to it. The calculations will let you know of the content of alcohol in the solution. Specific gravity can be a useful tool here as the formulas will be easy to use once if we are clear about the numerical value of specific gravity. 

For Wine:

ABV ~ 136* (Initial SG – Final SG)

For Beer:

ABV ~ 131* (Initial SG – Final SG) 

OR

ABV = (1.05/0.79)* {(Initial SG – Final SG) / Final SG} * 100

Apart from the few prescribed methodologies and the ABV calculator, there are some traditional methods that are also well known, one such method is alcohol proof. In this methodology, the alcohol content on the bottle is written by multiplying the ABV with 2. However, this can raise a conflict of understanding as every country might not have the same methodology and the alcohol proof written on the bottle can be mistaken with that the original content in the bottle. Other one on the same trail is alcohol by weight (ABW). This is widely popular in the USA and India as the respective government calculates tax on the basis of alcohol by weight (ABW) expressed as the percentage of the overall mass. However, in some scenarios the ABV is printed in spite of ABW. Why all this information? Because you can easily convert ABW into ABV. As ABW is known to calculate the solution’s mass which is, in turn, the mass of the alcohol and ABV is all about the volume of alcohol is respect to the solution so it can be easily converted into each other.

What if I Mix Two Types of Alcohol then?

Volume change:

Mixing two solutions of alcohol of different strengths often cause a change in volume. Mixing pure water with a solution less than 24% by mass results in a slight increase in total volume, whereas the mixing of two solutions above 24% results in a decrease in volume.

The phenomenon of volume changes due to mixing dissimilar solutions is termed as ” partial molar volume”.

Both water and ethanol are polar solvents. When water is added to ethanol, the smaller water molecules are interested in the ethanol’s hydroxyl, and every molecule alters the polarity field. The attraction allows the closer spacing between molecules than the usually found in non-polar mixtures.

Hence ABV is not the same as volume fraction expressed as a percentage. Volume fraction, which is widely utilized in chemistry (often denoted as v/v), is defined because the volume of a specific component divided by the sum of all components in the mixture when they are measured separately.

For example:  In order to make 100mL of 50% ABV ethanol solution, water would be added to 50mL of ethanol to make up exactly 100mL, whereas to make a 50% v/v ethanol solution 50 mL of ethanol and 50 mL of water might be mixed but the resulting volume of solution will measure but 100 mL thanks to the change of volume on mixing, and can contain a better concentration of ethanol.

The difference isn’t large, with the utmost difference being but 2.5%, and fewer than 0.5% difference for concentrations under 20%.

So, this was it, now you can check the alcohol content anytime all by yourself.