180 u00b0 f to about 205 u00b0 f have been found desirable most preferably temperatures within the range of 190 u00b0 f to about 205 u00b0 f in actual practice one common technique is to stir the salt into a water solution while simultaneously injecting steam to elevate the temperature within the desired range in accordance with the process of our prior patent u s pat no 4 764 633 along with these reactants a catalytically effective amount of ferric ion is added to enhance complexation yield the amount added is from about 2 to about 10 based upon the dry weight of methionine the earlier patent teaches that levels above the 10 molar percent level based upon the dry weight of methionine should be avoided this corresponds to the same molar percentages for zinc i e 2 to 10 and preferably 4 to 8 as previously mentioned in the earlier patent it was discovered that when percentages of ferric ion are added to the reactants at the levels there specified desirable things occur in the first instance the dissolving of the salt and the amino acid in the water appears to be significantly enhanced and in the second instance there is an increased yield of the desirable 1 1 complexes formed that earlier discovery however involved formation of the reactants and did not involve solving the problems that zinc and manganese methionine complexes are inherently difficultly soluble at best after formation it has now been surprisingly discovered that if substantially increased amounts of ferric ion are added during the formation reaction for the complexes not only does one get a substantially increased yield of the desirable.