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THE NITROGENOUS COMPLEXES OF HAZE AND FOAM AND THEIR MEASUREMENT
Author(s) -
Bishop L. R.
Publication year - 1977
Publication title -
journal of the institute of brewing
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.523
H-Index - 51
eISSN - 2050-0416
pISSN - 0046-9750
DOI - 10.1002/j.2050-0416.1977.tb03824.x
Subject(s) - chemistry , bromophenol blue , reagent , polyphenol , precipitation , polymer , chromatography , organic chemistry , amino acid , biochemistry , physics , meteorology , antioxidant
Earlier work and a review of recent studies have led to the view that the complex nitrogenous substances of beers are all, to some extent, irreversibly co‐complexed either with glucose polymers or with polyphenols, or with both. Where amino‐groups are still free, there can, in addition, be reversible combination with complex acids in worts and beers. The proportions of these different types of co‐complex are considered to have important effects on beer properties, so that methods for the measurement of the amounts present are regarded as essential. With this as objective, it has been found that the relatively unmodified “free‐amino” nitrogenous complexes, as well as those co‐complexed with polyphenols, can be precipitated by suitable acidic dyes. The resulting precipitates can then be dissolved to give a simple and rapid colorimetric measurement of the amounts of these complexes present. By using the specific reagent polyvinyl pyrrolidone (AT) to absorb and remove the polyphenolic co‐complexes, the remaining “free‐amino” nitrogenous complexes can be precipitated alone, so that separate measures of both types can be obtained. Using bromophenol blue as the dye, some precipitation, mainly of the higher molecular weight fractions, occurs around pH 5 and by progressively lowering the pH to 3, or by progressively increasing the dye concentration, larger and larger amounts are precipitated to give a spectrum of the nitrogenous complexes present. Using a method based on these findings, wide variations have been found in the amount of different complexes in different beers. Studies have been made of the selective migration of complexes into foam and of the changes occuring during increase of haze. The methods have also been used to study the changes produced by proteolytic enzymes and by silica gel absorption, as well as those produced by changes in the nitrogen content of malts used. In one stout, dye‐precipitable complexes are present in very small amounts. It appears that only non‐reactive “crypto‐nitrogenous” co‐complexes persist after the prolonged mashing period used: a rapid method of measurement has been found for these also.