Determine nitrogen in 3 grams of the sample by the Kjeldahl or Gunning
method. This gives the total nitrogen due to both the proteids and the
caffein. To obtain the protein nitrogen, subtract from the total
nitrogen the nitrogen due to caffein, obtained by direct determination
on the separated caffein or by calculation (caffein divided by 3.464
gives nitrogen). Multiply by 6.25 to obtain the amount of protein.