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 the high-molecular weight proteins in wort and beer by precipitating them with magnesium sulfate
This method is suitable for wort and beer.
The high molecular weight proteins are precipitated by magnesium sulfate, and the nitrogen content in the sediment is determined, e.g., according to Kjeldahl.
In order to measure the portion of the high molecular weight protein fractions in wort and beer, precipitation with magnesium sulfate is recommended. Through gel chromatography it has been established that magnesium sulfate precipitates nitrogenous compounds possessing molecular weights of approximately 2600 Da and higher [2]. A strong correlation between the nitrogenous substances precipitated by magnesium sulfate and beer foam has also been observed [3, 4].