Spectrophotometric Evaluation of Tannin Content in Domestic Beer Samples with Fe(III) and 1,10-Phenanthroline

Abstract

Tannins are polyphenolic compounds that can be divided into two groups by hydrolyzing and condensing. Tannins are produced in organisms of vascular plants called tannosomes and sequestered in vacuoles. The essential uses of tannins are in leather production, as adhesives, additives for wine, beer and fruit juices, etc. They are most present in the growing tissues of the plant as a crust, so beer that ripens in new oak barrels will contain a higher concentration of tannins. Tannins are extracted from malt during grinding and from the hops during cooking. The objective of this research is to determine the tannins content in twelve domestic beer samples (three samples of dark beer and nine samples of light beer) by spectrophotometric method. The method is based on the reduction of Fe(III) to Fe(II) by tannins. The iron(II) reacts with 1,10-phenanthroline at pH 4.4 to form a color complex. The absorbance measurements were made at 540 nm. As a standard tannic acid was used, tannin content was in range 15.49-1722.05 μg/mL. Tannins are present in all beers, above the threshold of detection. When tannins are present in excess, they negatively impact beer by causing astringency but beer completely devoid of tannins does not taste right.