Search: Phenol

Analysis was performed using isocratic HPLC on a Spherisorb separation column with UV detection at 260 nm.

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 %

The aromatic alcohols in beer are isolated using solid-phase extraction and are detected using gas chromatography-mass spectrometry.

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).

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.

Aside from evaluating the criteria flavor, fullness, liveliness and bitterness, based on the DLG Quality Assessment for Beer (refer to S.590.53.700 Einzelprobenprüfung zur Qualitätskontrolle von Bier - DLG-Prüfschema für Bier), the additional gustatory impressions of the four prevailing Southern German wheat beer styles are examined more closely. Thus, the sensory intensity and quality of the estery, phenolic, yeasty and malty notes in these beers can be assessed. Estery beers exhibit an evident fruitiness, of which the banana-like aroma of isoamyl acetate is the most prevalent. Wheat beers of the phenolic variety impart a clove-like impression, primarily due to 4-vinyl guaiacol, which at higher concentrations can be perceived as medicinal. Yeasty beers can exhibit a wide range of flavor-active fermentation by-products; however, old yeast and sulfur notes tend to dominate. Except of course for malty notes, wheat beers of a more malty or neutral character do not usually possess a distinctive aroma. The criteria are evaluated on a five-point scale, with 5 considered to be “pure” and 1 as “exhibiting major faults”. Scores are also possible in half-point steps.