Lesson 4 - Wort and Beer Analysis

It is a legal requirement in some countries to list the nutritional information on the package of beer. Of most interest to the consumer is probably the calorific content. We now look at how to determine this for beer.

The standard method of determining the calorific content of beer is to calculate it based on the measurement of its calorific components. The calculation is:

Energy (kJ/100g)=(17 x carbohydrate weight)+(10 x polyols weight)+(17 x protein weight)+(37 x fat weight)+(29 x alcohol weight)+(13 x organic acid weight)+(8 x fibre weight)

Each factor (multiplying number) above relates to the kilojoules per gram of the component. Each of the brewing organisations has its own recommended method for the calculation. They are all a simplification of the calculation above.    

The EBC method uses the follow calculation, where ϱ is density of beer (kg/L), E_r is real extract in %w/w, and 15 is an energy value which accounts for the expected ratio of the components of extract (all of which will contribute differing amounts of energy):

This is a convenient calculation and it enables the Alcolyzer to calculate a calorific value for the beer from the elements it analyses. It is quite accurate for standard beers but is inaccurate for alcohol-free beers, shandy, and radlers.

MEBAK recommends two calculations. The first is the same as the EBC equation above and the second separates out the components of the extract to an extent:

The total content of carbohydrates in beer is determined by the following method. First we hydrolyse and dehydrate carbohydrates with 85% v/v sulphuric acid to form 5-hydroxymethylfurfural. We then add anthrone to produce a blue-green colour. We measure the absorbance of the solution at 625 nm and use the figure to calculate the concentration of carbohydrates.

To calculate the protein in beer, we take the total nitrogen figure provided by the Kjeldahl method (discussed earlier in this lesson) and multiply it by 6.25. The alcohol by weight can be found by the distillation or GC methods we covered earlier.

The ASBC use this calculation:

This calculation corrects for the contribution of non-calorific salts to the weight of the extract by subtracting the ash content.