Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
In an acidic solution, in the presence of ammonium molybdate, dissolved silicic acid or silicates produce silicomolybdic acid which exhibits a yellow color. After the addition of a reducing agent, a blue color emerges which is proportional to the quantity of the silicic acid present in a certain concentration range.
Valid for all non-turbid beers
By incrementally adding increasing amounts of a saturated ammonium sulfate solution to beer, haze appears as a result of protein precipitation. The amount of the ammonium sulfate solution necessary to produce haze is directly proportional to the stability of the beer. The ammonium sulfate precipitation value expresses the ml of saturated ammonium sulfate solution that must be added to 100 ml of beer in order to produce a barely perceptible opalescence.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
Ammonium ions react at a pH of approx. 12.6 with hypochlorite ions and salicylate ions in the presence of sodium nitroprusside, which serves to catalyze the reaction, to form a green color (indophenol blue).
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.
The method describes how to determine the phosphate content of water photometrically with a cuvette test.
Phosphate ions form a yellow color in the presence of the molybdovanadate reagent. The color is determined using a photometer.
Determination of the concentration of quaternary ammonium compounds (QAV) in disinfectants.
Suitable for all solutions containing quaternary ammonium compounds (QAV).
Many basic dyes (e.g. methylene blue) behave in a similar way to cation-active substances. Methylene blue forms a complex with dodecyl sulfate (anion-active surfactant), for example, which is soluble in organic solvents such as dichloromethane with blue colour. By adding quaternary ammonium compounds (QAV), this complex is decomposed and the methylene blue migrates from the dichloromethane into the aqueous phase. When titrating quaternary ammonium compounds with dodecyl sulfate, this process takes place in the opposite direction, i.e. the methylene blue migrates from the aqueous to the dichloromethane phase. The end point of the titration is reached when the aqueous and dichloromethane phases have the same colour depth.
Or to put it in other words:
Methylene blue (water-soluble dye in cationic form) forms a complex with dodecyl sulfate (anionic surfactant), which is soluble in organic solvents, e.g. dichloromethane, with blue colour. On the other hand, QAV also forms a complex with dodecyl sulfate, so that the indicator migrates into the organic phase once the equivalence point has been exceeded.