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The Determination of Tannic Substances in Commercial Cocoa Powders

Massachusetts State College, Amherst, Massachusetts

ABSTRACT

1. Fifteen samples of commercial cocoa powders were analyzed, presumably for cacao-purple, by Ulrich's ferric chloride precipitate method. The ferric chloride precipitates ranged from 3.48 to 15.59 per cent, with an average of 11 per cent. The average percentage of ferric chloride precipitate obtained from Dutch cocoas was approximately one-third of the amount obtained from the unprocessed cocoas.
   
2. The amount of ferric chloride precipitate does not measure accurately the amount of cacao-purple or other tannic substances in cocoa, partly because the ash content of the precipitate was found to be relatively high, averaging 13.45 per cent.
   
3. The ash consisted mainly of iron and phosporus, present either as separate oxides or in combination as ferric phosphate.
   
4. A modification of the method of washing the ferric chloride precipitate has been suggested, which reduced its ash content.
   
5. Results obtained from this study indicate that the ferric chloride precipitate would measure the tannic substances content of cocoa more accurately if the modification of the washing procedure were followed and correction made for the ash contained.
   

¹ Department of Dairy Industry and Control Service Cooperating, Contribution No. 514 of the Massachusetts Agricultural Experiment Station.