Titrate the excess silver with N/10 ammonium or potassium thiocyanate until a permanent light brown color appears.
"All About Coffee" by William H. Ukers
The double thiocyanate, Cr(SCN)3.3KCNS.4H2O, is also known.
"Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 3" by Various
C.; but best by heating ammonium thiocyanate to 180 deg.-190 deg.
"Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 6" by Various