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Comparison of Dumas and Kjeldahl Method for Nitrogen Determination in Malt, Wort and Beer
M. Kupetz, C. Geiinger, M. Gastl and T. Becker

Depending on the molar distribution, nitrogen has not only an important influence in yeast nutrition, but also on foam and haze stability of beer. Thus, it is important to have information on the nitrogen content of used grain, malt and produced wort. Over the years, various methods were described for the determination of nitrogen, with Kjeldahl and Dumas method being the most popular applications. However, according to literature, nitrogen contents of the methods are difficult to compare, because Kjeldahl method mainly measures organic nitrogen, whereas Dumas method determines total nitrogen content. Due to some advantages in terms of elimination of toxic reagents as well as shorter analysis time of Dumas methodology it would be a good alternative for application in the brewing industry. Comparison of the two nitrogen measurement methods was carried out with automated analyzers in barley malt (n = 408), wheat malt (n = 109) and wort or beer (n = 174). Besides a good repeatability of Dumas method (0.05 %) for barley malt, a significant correlation of r = 0.969 (P < 0.001) to Kjeldahl nitrogen could be determined. Comparable results were found for wheat malt (r = 0.932, P < 0.001) and wort (r = 0.981, P < 0.001). Variance analysis by means of t-test showed no significant differences in the repeated measurements between the two methods. Due to the good comparability as well as advantages in terms of occupational safety and faster analysis time, the Dumas method can be used for determining the nitrogen content in malt, wort and beer.

Descriptors: soluble nitrogen, protein, combustion method, Kjeldahl method

BrewingScience, 71 (March/April 2018), pp. 18-23