The conventional isolation method has been modified in order to minimize protein contamination of tannin purified from high tannin sorghum. The two unique steps of the new procedure are preliminary extraction of the ground grain with ethanol and treatment of the partially purified tannin with phenol to remove traces of noncovalently bound protein. Tannin-associated protein removed by phenol treatment is not a random mixture of all the seed proteins, but consists of several discrete components which have been isolated and partially characterized. These proteins are quite hydrophobic, and one is rich in proline. With only minor changes, the purification method can be used to isolate tannin from seeds of other plants such as legumes