Hops and hop products intended for use in beer brewing or elsewhere in the food industry
The polyphenols are extracted from the hops using hot water. In an alkaline environment, they form a red pigment with iron (III) ions, which is measured spectrophotometrically at 600 nm.
Determination of the total polyphenol content
This method is suitable for wort, beer and other beverages
Polyphenols react with ferric iron (Fe3+) in an alkaline solution, forming iron complexes. The complexes created by the reaction yield a brownish color, which is measured spectrophotometrically at 600 nm [2].
This method is suitable for (bottom-fermented) beer and beverages.
The fraction of phenols extracted using steam are converted to color complex using 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (4-aminophenazone) in an alkaline medium and through oxidation with potassium ferrocyanide (III), which can be measured spectrophotometrically after extraction with chloroform (fig. 1).
Water intended for use in beer brewing as well as in the production of other foods
Steam-volatile phenols form by bonding with diazotized p-nitroaniline azo dyes; the intensity of the resultant color is measured photometrically following extraction with n-butanol.
The intensity of the color, based on a saturation threshold of phenol of 100 %, is as follows:
phenol 100 % m-xylenol 52 %
o-cresol 147 % p-xylenol 92 %
m-cresol 120 % guaiacol 165 %
p-cresol 21 % pyrocatechol 29 %
o-xylenol 16 % α-naphthol 23 %
This method is suitable for wort, beer and other beverages.
Anthocyanogens adsorb onto polyamide, and this adsorbate is dissolved in butanol hydrochloric acid and heated, causing a red color to develop, which is then measured spectrophotometrically.
This method is suitable for barley, malt, hops, wort, beer and other beverages
The tannoid content of beer and wort as well as the content in barley, malt and hop extract can be determined through precipitation with polyvinylpyrrolidone (PVP), which has a structure similar to protein in that tannoids attach to it by means of hydrogen bonds. As a result, PVP and tannoids form insoluble complexes, which produce turbidity. If PVP is continuously metered into the sample, the turbidity will constantly increase until all of the tannoid molecules are attached to the PVP; however, if the PVP continues to be added to the sample after that point, then the turbidity will begin to decrease. The quantity of PVP required to reach the maximum level of turbidity is proportional to the tannoid content. The Tannometer, therefore, measures the turbidity relative to the quantity of added PVP and expresses the tannoid content of the sample in mg/l of PVP.