The following nitrogenous substances are found in wort and beer:
Amino acids, peptides, proteins, nucleic acids and their derivates, ammonium salts, nitrates, heterocyclic compounds as well as aliphatic and aromatic amines. In practical applications, amino acids, peptides, proteins and ammonium salts are of particular interest. The amino acids and ammonium salts are the most important sources of nitrogen for the yeast. They shape to a large extent which fermentation by-products are created through yeast metabolism and at which concentrations. The medium and high molecular weight proteinaceous compounds (peptides, proteins) are especially significant for the colloidal stability (shelf life), mouthfeel and for foam stability. For this reason, it is necessary to measure not only the total amount of protein but also the relative amounts of each of the proteinaceous compounds in wort and beer.
Determination of nitrogenous compounds in beer and wort (crude protein) detectable using Kjeldahl digestion
This method is suitable for wort and beer.
Nitrogen determination according to Kjeldahl is divided into the following steps:
Digestion of the sample (oxidation of proteins to H2O, CO2 and NH3), during which the NH3 is carried over in (NH4)2SO4 using H2SO4
Distillation (distillation of NH3 over into a boric acid solution)
Titration (determination of the amount of NH3 present in the receiver after distillation) [1]