Determination of low-molecular weight nitrogenous compounds in wort and beer (< 2600 Da) by means of molybdate precipitation
This method is suitable for wort and beer.
Determination of low-molecular weight nitrogenous compounds in wort and beer (< 2600 Da) after precipitating the high and middle-molecular weight nitrogenous compounds with molybdate
The nitrogen content in the filtrate is determined using Kjeldahl or Dumas.
Precipitation with phosphomolybdic acid provides information regarding the medium molecular weight nitrogenous substances present in samples of wort and beer. Nitrogenous substances with a molecular weight greater than 2600 Da are precipitated [1]. However, a quantitative elimination of all nitrogenous substances of an equivalent molecular weight does not occur, which indicates specificity toward certain nitrogenous substances.
Nitrogenous substances of a medium molecular weight can be calculated as the difference between the nitrogenous substances precipitated with molybdic acid and those precipitated with magnesium sulfate [2, 3].
The reagent phosphomolybdic acid itself is not necessary for the analysis; a solution of sodium molybdate is sufficient. Through the addition of sulfuric acid, enough phosphoric acid is released from the phosphates present in wort and beer to form phosphomolybdic acid.
This analysis is suitable for determining the sulfate content of beer, wort, water, NAB and fruit juice.
Sulfate ions are precipitated with barium ions in the form of barium sulfate and determined gravimetrically.
The method describes how to determine the sulfate content of water through precipitation.
Barium chloride sulfate is precipitated as coarse crystalline barium sulfate. The precipitate is determined gravimetrically:
SO42- + Ba2+ → BaSO4