Determination of the vicinal diketone content (diacetyl + 2,3-pentanedione) as well as the total diketone content in beer
The method is suitable for filtered beers brewed to any original wort or to any alcohol content as well as for fermenting wort.
Diacetyl (2,3-butanedione) and 2,3-pentanedione are detected photometrically in the beer after steam distillation. It is also possible to determine precursors in green beer.
Determination of maltose and maltotriose by enzymatic means
Suitable for wort, beer, malt beverages, nutrient beer, mixed beer beverages, NAB, juices and beverages.
Maltose is the main component of beer wort or wort extract.
Maltose and sucrose are cleaved by the enzyme α-glucosidase (maltase) at pH 6.6 into two molecules of D-glucose and D-fructose, respectively:
\(\text{Maltose}+H_2O \hspace{0.8em} \xrightarrow{α–glucosidase} \hspace{0.8em} {2 \hspace{0.2em} \text{D–glucose}}\)
\(\text{Sucrose}+H_2O \hspace{0.8em} \xrightarrow{α–glucosidase} \hspace{0.8em} {\text{D–glucose}+\text{D–fructose}}\)
The D-glucose formed is phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P):
\(\text{Glucose}+\text{ATP} \hspace{0.8em} \xrightarrow{HK} \hspace{0.8em} \text{G-6-P} \hspace{0.2em} + \hspace{0.2em} \text{ADP}\)
In the presence of the enzyme glucose-6-phosphate dehydrogenase (G6P-DH), G-6-P is oxidized from nicotinamide adenine dinucleotide phosphate (NADP) to gluconate-6-phosphate. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is formed:
\(\text{G-6-P} \hspace{0.2em} + \hspace{0.2em} \text{NADP}^+ \hspace{0.8em} \xrightarrow{G6P-DH} \hspace{0.8em} \text{gluconate-6-phosphate} \hspace{0.2em} + \hspace{0.2em} \text{NADP}^+ \hspace{0.2em} + \hspace{0.2em} \text{H}^+\)
The amount of NADPH formed during the reaction is equivalent to the amount of glucose. NADPH is measurand and is determined based on its absorbance at 334, 340 or 365 nm.
The enzyme α-glucosidase is group specific, i.e., the specificity is directed to the type of glycosidic bond.
Only α-1,4 bonds, i.e., in addition to maltose, sucrose and maltotriose, but not maltotetraose, are cleaved under the given conditions. Therefore, the sucrose content must be taken into account in the maltose calculation (the maltose approach records the glucose formed from maltose and sucrose and the free glucose, the sucrose approach records the glucose formed from sucrose and the free glucose).
Determination of organic acids using ion chromatography
This method is suitable for beer, wort, green beer, NAB, water and wastewater
Separation by ion chromatography followed by conductivity detection.
Analysis of the chloride content of beer, wort, water, NAB and other beverages
The analysis method can be employed for determining the chloride content of beer, wort, water, NAB and other beverages.
Chloride ions are precipitated with silver nitrate as silver chloride. The endpoint of the titration can be determined by means of a conductometer. The conductivity increases as soon as all of the chloride ions are eliminated, causing the concentration of the unbound silver nitrate to increase.
Determination of total diacetyl in beer.
The method is suitable for beers of all original wort ranges and alcohol contents.
Beer is thermally treated to cause the precursors present in the sample to transform into their respective vicinal diketones. Using the headspace technique, the concentration of total diacetyl is determined using gas chromatography. The linearity of the detector and the determination of the concentrations of analytes in the sample are achieved by using multiple concentration levels within their relevant range and through evaluation of the relative area under the peaks. Depending upon the operating conditions of the chromatograph, the relative areas under the peaks can also be used to determine the concentrations. The method is suitable for beer brewed to any original gravity or to any alcohol content.
Determination of the content of 2,3-butanedione (diacetyl) and 2,3-pentanedione or the content of total VDK (free VDKs and precursors) after thermal conversion of the precursors
The method is suitable for beer brewed to any original gravity or to any alcohol content as well as for fermenting wort.
Diacetyl, 2,3-pentanedione and their precursors are determined by means of gas chromatography. A sample from the headspace – in equilibrium with the beer at 35 °C – is analyzed. Precursors are converted to the corresponding diketones through aeration and heating the beer to 60 °C. The evaluation of the results is performed by comparing the height of the peaks of diacetyl and against the peak for hexanedione as the internal standard.