Alcohol

The alcohol level is beer characteristic that is commonly expressed as vol%. To assist at measurments we usually use hydrometer or refractometer. The measurments should be done at temperature of calibration (this data is written on refractometer or hydrometer), otherwise the measurments will not be correct. Otherwise you can use corrections.

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1. Units

ABV (alcohol by volume) Units: vol%
°brix (amount of sugar present in liquid)
OG (original gravity)
FG (final gravity)
1,05 g (amount of CO2 produced for every gram of ethanol produced)
0,79 g/ml (density of ethanol)

2. Equations

 If we use refractometer to measure gravity we get results in units of °Brix, so we need to calculate gravity from this measurment

Specific gravity = (0,004 x °Brix) + 1

If we use hydrometer, we do not need to use equation above

ABV(%) = ((1,05 x (OG – FG)) / FG) / 0,79 x 100

3. Calculation

So, how to calculate alcohol % on example?
We have 2 examples, one if we use refractometer and another if we use hydrometer.

Example 1:
We made a measurments with refractometer, we measured original gravity (OG) before start of fermentation and it was 14 °Brix. After fermentation we made new measurment and the result final gravity (FG) was 4 °Brix.

Step 1: we will calculate specific gravity (OG and FG)
OG = (0,004 x 14) + 1 = 1,056
FG = (0,004 x 4) + 1 =  1,016

Step 2: we will calculate ABV %
ABV(%) = ((1,05 x (1,056 – 1,016))/1,016) / 0,79 x 100 =
ABV(%) = 5,23 %

Example 2:
We made a measurments with hydrometer, we measured original gravity (OG) before start of fermentation and it was 1,062. After fermentation we made new measurment and the result final gravity (FG) was 1,018.

Step 1: we will calculate ABV %
ABV(%) = ((1,05 x (1,062 – 1,018))/1,018) / 0,79 x 100 =
ABV(%) = 5,74 %

So, we also learned how to calculate ABV%!