B-590.10.007 [2020-10] Original Gravity, Extract and Alcohol – Catalytic Combustion (SCABA)

In order to determine the real extract of a beer, the alcohol must be removed by means of distillation and water added to the residue until the original weight is reached. Only then does the saccharometer convey the value of the real extract. The alcohol content of a beer is determined using the distillate.

During fermentation, 1 g of alcohol, 0.9565 g of carbon dioxide and 0.11 g of yeast are produced on average from 2.0665 g of extract.

Prior to distillation, the carbon dioxide and yeast (1.0665 g combined) are removed from the beer.

The original gravity (p) of the beer can be calculated from the % mass or % w/w measured for the alcohol content (A) and real extract (E_R).

For every gram of alcohol contained in the beer, an average of approximately 2.0665 g of extract is fermented. Thus, the amount of fermented extract in g/100 g is calculated as follows:

A × 2.0665

The total grams of extract present in 100 g of beer prior to fermentation (wort) is calculated from masses of the unfermented extract (E_R) and the fermented extract as follows:

A × 2.0665 + E_R

Due to removal of the yeast and carbon dioxide, the beer possesses less mass than the original wort; therefore, the masses of both must be added to 100 g of beer for every gram of alcohol as follows:

100 + A × (0.9565 + 0.11) = 100 + A × 1.06654

For this reason, the mass (g) of wort expressed in term 1 originally contained the mass (g) of extract shown in term 2:

100 + A × 1.0665 (1)

A × 2.0665 + E_R (2)

This relationship can be formulated as follows:

\(\text{p in % w/w} = {\space (A \space × \space 2.0665 \space + \space E_R ) \space × \space 100 \over A \space × \space 1.0665 \space + \space 100}\)

Increasingly, devices designed to analyze beer are replacing the classic methods based on distillation or refractometry. These devices are often automated, combine diverse analyses and can analyze a large number of beer samples with a high degree of reproducibility. They either combine previously described methods (oscillating U-tube densimeter/refractometer combination) or employ new techniques, which are described below. For automated measuring devices, it is imperative that samples waiting to be analyzed are covered appropriately, in order to avoid evaporation of the alcohol in the samples.

The analysis methods for determining original gravity, apparent extract and the alcohol content of beer-based beverages are comparable to the same methods for beer, and no consideration is given to the fact that a portion of the extract originates from soft drinks added to the beer. The kind of sweetener such as sugar (sucrose, glucose, fructose), artificial sweeteners or a mixture of the two (combined sweeteners) in the soft drink are also irrelevant for purposes of analysis.

For beer-based beverages sweetened with sugar, the soft drink portion of the beverage is also subject to the same taxation regulating beer sales, while those sweetened with artificial sweeteners are not, due to their almost negligible extract content.