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Zinc in wort is measured using the AAS technique by directly aspirating the diluted sample into an acetylene oxygen flame or through electrothermal atomization; the measurement is made at 213.9 nm.

Low molecular weight nitrogenous substances, especially amino acids in the wort, have an influence on the course of fermentation and the formation of fermentation by-products. For a beer’s aroma profile, the concentration and composition of the amino acids are therefore of considerable significance due to their reactivity with reducing sugars (Maillard reaction), especially during kilning in the malthouse and during mashing and boiling in the brewhouse. The products from these reactions influence the redox potential, the color and the aroma of a beer.

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. 

The ninhydrin reaction is the most well-known of the color reactions employed for use with amino acids. Ninhydrin is an oxidant and brings about the oxidative decarboxylation of amino acids, producing CO₂, NH₃ and the formation of an aldehyde. The aldehyde produced in this reaction possesses one less carbon atom than the original amino acid that served as the reactant. Reduced ninhydrin then reacts with non-reduced ninhydrin and the NH₃ that was liberated to generate a blue pigment (all amino acids except for proline) or in the case of proline, a yellow pigment. Fructose also takes part in the color reaction as a reducing compound. Potassium iodide present in the solution used for dilution preserves the ninhydrin in an oxidized state and thus inhibits undesirable secondary reactions. The solution to be analyzed is heated together with ninhydrin at a pH of 6.7 and the resulting color is measured at 570 nm. 

This method quantifies the amino acids, ammonia and also the terminal α-amino groups of the peptides and proteins. Proline is also measured in part at the wavelength employed in this method.

The method is non-specific for α-amino nitrogen, because γ-amino butyric acid found in wort also generates a color reaction in the presence of ninhydrin.

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. 
 

The pH value of the Congress wort allows for a cursory estimate of the acidifying capacity of the acidulated malt in question. If a deeper understanding is required, then determining the titratable acidity or the lactic acid content would be necessary.

L-lactic acid (L-lactate) is oxidized by nicotinamide adenine dinucleotide (NAD) in the presence of L-lactate dehydrogenase (L-LDH) to pyruvic acid. For oxidation of D-lactic acid, the enzyme D-lactate dehydrogenase (D-LDH) is required.

The equilibrium of these reactions is much closer to lactate. The equilibrium can be shifted towards the pyruvate and NADH side of the equation by removing the pyruvate with the help of the following reaction involving the enzyme glutamate-pyruvate transaminase (GPT) in the presence of L-glutamate.

The amount of NADH formed during the reactions is equivalent to the amount of lactic acid or D-lactic acid; the absorbance is determined photometrically at 334, 340 or 365 nm.