The method describes how to determine the amino acids present in the filtered malt mash or (Congress) wort by means of reverse phase chromatography.
Low molecular weight nitrogenous compounds, especially amino acids in the wort, impact the course of fermentation and the formation of fermentation by-products. Therefore, the concentration and composition of the amino acids are important for the aroma profile of beer; in addition, their reactivity with reducing sugars (Maillard reaction) is of considerable consequence, especially during the kilning of the malt and in the brewhouse during mashing or the boil. These reaction products influence the redox potential, color and aroma of the beer.
Applicable for all (laboratory) worts
The quantitative determination described here is based upon a separation of analytes using reverse phase chromatography after pre-column derivatization and detection with fluorescence detection.
Aside from the quantitative determination of the individual amino acids (methods using an ion exchanger, HPLC, GC), cumulative methods of determination are customary. However, these methods also measure NH4+ ions and amines to some degree.
With methods involving color reactions, the amino acids display color at different levels of intensity. Therefore, the reaction is based upon a “standard amino acid”; glycine usually serves as the standard amino acid for comparison.
With the ninhydrin method, the color yield varies with the individual amino acids between 70 and 105 %, based on glycine. Up to approx. 30 % of ammonium salts are quantified using this method and up to approx. 7 % of proline.