Phenolic compounds originate in malt and hops. The amount of these compounds present in the finished beer is largely dependent on the technology and equipment used to brew the beer. The structure and size of the molecules determines to what extent they affect the various attributes of the finished beer, such as color, flavor, flavor stability, foam as well as chemical-physical stability. Under less than optimal conditions, for instance given a high concentration of compounds with a proclivity for polymerization, condensation or the presence of air (oxygen), the resultant compounds with the ability to precipitate proteins, possess an undesirable flavor.
Steam-volatile phenols stemming from the brewing liquor or the malt or perhaps even from microbial contamination somewhere in the brewing process can impart a flawed aroma to the finished beer.
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).