Total Sulfur Dioxide (SO2)  in Beer

Sulfur dioxide is an important parameter in the beer brewing process.

Sulfur dioxide (SO2) works as an antioxidant and is important for the shelf life of beer. However, SO2 levels in beer need to be strictly monitored, because high concentrations of SO2 in beer can cause allergic reactions.


A variety of analytical methods are available for the determination of SO2 in beer. Often, the colorimetric EBC method 9.25.3 or comparable  ASBC method, Beer-21 para-rosaniline (p-rosaniline) is used.  More and more breweries are looking for a less toxic alternative method for analyzing SO2. Therefore Skalar developed a new automated method on the San++ continuous flow analyzer for determining Total SO2 in beer. The automated method is based on the well known 5’-dinitrobenzoic acid (DTNB ) method. 

Principle automated DTNB procedure
The beer sample is diluted in a sulfuric acid solution and heated at 90 °C to release the bound sulfur dioxide. Gaseous sulfur dioxide is formed, which is dialyzed into a phosphate buffer solution. Hereafter it reacts with the DTNB-solution to form the bright yellow 2-nitro-5-thiobenzoate. The absorption is measured at 410 nm.

Several beer samples have been analyzed on the San++ continuous flow analyzer. The results can be found in the graph below  SO2 in both methods.

Comparison DTNB/Para-R method for SO2








Comparison DTNB/Para-R method for SO2

The automated DTNB method for the determination of Total SO2 on the San++ gives comparable results to the classical p-rosaniline method. The San++ analyzer  provides fully automatic accurate and reproducible results for Total SO2 on large series of samples.

In addition, the San++ analyzer easily combines the Total SO2  application with other beer parameters such as Bitterness, F.A.N., Polyphenol and many others.


  1. European Brewery Commission (EBC) method 9.25.3
  2. American Society of Brewing Chemists (ASBC), Beer-21 para-rosaniline (p-rosaniline)
  3. Guido, L.F., (2005) How do sulphites help to control beer ageing? Cerevisia, 30(2), pp. 132-137

For more information about the Total SO2 method or other applications/questions, please contact Skalar:

A pdf of this new application can be downloaded here.