The Estimation of Tannin in Cider

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Abstract
The method at present in use for the estimation of tannin in apple juice and cider is that used by Lloyd. It is a modification according to Kraus of Löwenthal's method, and consists in titrating the cider directly with potassium permanganate in presence of indigo as an indicator. The permanganate is standardized by means of “pure tannin,” it being assumed that both this and the tannin present in the apple are digallic acid, and have the composition C14H10O9. It is apparent that all the permanganate reducing substances present in the cider will be included in the tannin content; moreover the amount of indigo used is not sufficient to retard noticeably the oxidation of the non-tannins for which purpose it was originally used in Löwenthal's method. The results obtained by this method are therefore only comparative.

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